Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1451 insertions, 0 deletions

diff --git a/intl/icu/source/common/ustrtrns.cpp b/intl/icu/source/common/ustrtrns.cpp
new file mode 100644
index 0000000000..244c111fc4
--- /dev/null
+++ b/intl/icu/source/common/ustrtrns.cpp
@@ -0,0 +1,1451 @@
+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+******************************************************************************
+*
+*   Copyright (C) 2001-2016, International Business Machines
+*   Corporation and others.  All Rights Reserved.
+*
+******************************************************************************
+*
+* File ustrtrns.cpp
+*
+* Modification History:
+*
+*   Date        Name        Description
+*   9/10/2001    Ram    Creation.
+******************************************************************************
+*/
+
+/*******************************************************************************
+ *
+ * u_strTo* and u_strFrom* APIs
+ * WCS functions moved to ustr_wcs.c for better modularization
+ *
+ *******************************************************************************
+ */
+
+
+#include "unicode/putil.h"
+#include "unicode/ustring.h"
+#include "unicode/utf.h"
+#include "unicode/utf8.h"
+#include "unicode/utf16.h"
+#include "cstring.h"
+#include "cmemory.h"
+#include "ustr_imp.h"
+#include "uassert.h"
+
+U_CAPI char16_t* U_EXPORT2
+u_strFromUTF32WithSub(char16_t *dest,
+               int32_t destCapacity,
+               int32_t *pDestLength,
+               const UChar32 *src,
+               int32_t srcLength,
+               UChar32 subchar, int32_t *pNumSubstitutions,
+               UErrorCode *pErrorCode) {
+    const UChar32 *srcLimit;
+    UChar32 ch;
+    char16_t *destLimit;
+    char16_t *pDest;
+    int32_t reqLength;
+    int32_t numSubstitutions;
+
+    /* args check */
+    if(U_FAILURE(*pErrorCode)){
+        return nullptr;
+    }
+    if( (src==nullptr && srcLength!=0) || srcLength < -1 ||
+        (destCapacity<0) || (dest == nullptr && destCapacity > 0) ||
+        subchar > 0x10ffff || U_IS_SURROGATE(subchar)
+    ) {
+        *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        return nullptr;
+    }
+
+    if(pNumSubstitutions != nullptr) {
+        *pNumSubstitutions = 0;
+    }
+
+    pDest = dest;
+    destLimit = (dest!=nullptr)?(dest + destCapacity):nullptr;
+    reqLength = 0;
+    numSubstitutions = 0;
+
+    if(srcLength < 0) {
+        /* simple loop for conversion of a NUL-terminated BMP string */
+        while((ch=*src) != 0 &&
+              ((uint32_t)ch < 0xd800 || (0xe000 <= ch && ch <= 0xffff))) {
+            ++src;
+            if(pDest < destLimit) {
+                *pDest++ = (char16_t)ch;
+            } else {
+                ++reqLength;
+            }
+        }
+        srcLimit = src;
+        if(ch != 0) {
+            /* "complicated" case, find the end of the remaining string */
+            while(*++srcLimit != 0) {}
+        }
+    } else {
+      srcLimit = (src!=nullptr)?(src + srcLength):nullptr;
+    }
+
+    /* convert with length */
+    while(src < srcLimit) {
+        ch = *src++;
+        do {
+            /* usually "loops" once; twice only for writing subchar */
+            if((uint32_t)ch < 0xd800 || (0xe000 <= ch && ch <= 0xffff)) {
+                if(pDest < destLimit) {
+                    *pDest++ = (char16_t)ch;
+                } else {
+                    ++reqLength;
+                }
+                break;
+            } else if(0x10000 <= ch && ch <= 0x10ffff) {
+                if(pDest!=nullptr && ((pDest + 2) <= destLimit)) {
+                    *pDest++ = U16_LEAD(ch);
+                    *pDest++ = U16_TRAIL(ch);
+                } else {
+                    reqLength += 2;
+                }
+                break;
+            } else if((ch = subchar) < 0) {
+                /* surrogate code point, or not a Unicode code point at all */
+                *pErrorCode = U_INVALID_CHAR_FOUND;
+                return nullptr;
+            } else {
+                ++numSubstitutions;
+            }
+        } while(true);
+    }
+
+    reqLength += (int32_t)(pDest - dest);
+    if(pDestLength) {
+        *pDestLength = reqLength;
+    }
+    if(pNumSubstitutions != nullptr) {
+        *pNumSubstitutions = numSubstitutions;
+    }
+
+    /* Terminate the buffer */
+    u_terminateUChars(dest, destCapacity, reqLength, pErrorCode);
+    
+    return dest;
+}
+
+U_CAPI char16_t* U_EXPORT2
+u_strFromUTF32(char16_t *dest,
+               int32_t destCapacity, 
+               int32_t *pDestLength,
+               const UChar32 *src,
+               int32_t srcLength,
+               UErrorCode *pErrorCode) {
+    return u_strFromUTF32WithSub(
+            dest, destCapacity, pDestLength,
+            src, srcLength,
+            U_SENTINEL, nullptr,
+            pErrorCode);
+}
+
+U_CAPI UChar32* U_EXPORT2 
+u_strToUTF32WithSub(UChar32 *dest,
+             int32_t destCapacity,
+             int32_t *pDestLength,
+             const char16_t *src,
+             int32_t srcLength,
+             UChar32 subchar, int32_t *pNumSubstitutions,
+             UErrorCode *pErrorCode) {
+    const char16_t *srcLimit;
+    UChar32 ch;
+    char16_t ch2;
+    UChar32 *destLimit;
+    UChar32 *pDest;
+    int32_t reqLength;
+    int32_t numSubstitutions;
+
+    /* args check */
+    if(U_FAILURE(*pErrorCode)){
+        return nullptr;
+    }
+    if( (src==nullptr && srcLength!=0) || srcLength < -1 ||
+        (destCapacity<0) || (dest == nullptr && destCapacity > 0) ||
+        subchar > 0x10ffff || U_IS_SURROGATE(subchar)
+    ) {
+        *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        return nullptr;
+    }
+
+    if(pNumSubstitutions != nullptr) {
+        *pNumSubstitutions = 0;
+    }
+
+    pDest = dest;
+    destLimit = (dest!=nullptr)?(dest + destCapacity):nullptr;
+    reqLength = 0;
+    numSubstitutions = 0;
+
+    if(srcLength < 0) {
+        /* simple loop for conversion of a NUL-terminated BMP string */
+        while((ch=*src) != 0 && !U16_IS_SURROGATE(ch)) {
+            ++src;
+            if(pDest < destLimit) {
+                *pDest++ = ch;
+            } else {
+                ++reqLength;
+            }
+        }
+        srcLimit = src;
+        if(ch != 0) {
+            /* "complicated" case, find the end of the remaining string */
+            while(*++srcLimit != 0) {}
+        }
+    } else {
+        srcLimit = (src!=nullptr)?(src + srcLength):nullptr;
+    }
+
+    /* convert with length */
+    while(src < srcLimit) {
+        ch = *src++;
+        if(!U16_IS_SURROGATE(ch)) {
+            /* write or count ch below */
+        } else if(U16_IS_SURROGATE_LEAD(ch) && src < srcLimit && U16_IS_TRAIL(ch2 = *src)) {
+            ++src;
+            ch = U16_GET_SUPPLEMENTARY(ch, ch2);
+        } else if((ch = subchar) < 0) {
+            /* unpaired surrogate */
+            *pErrorCode = U_INVALID_CHAR_FOUND;
+            return nullptr;
+        } else {
+            ++numSubstitutions;
+        }
+        if(pDest < destLimit) {
+            *pDest++ = ch;
+        } else {
+            ++reqLength;
+        }
+    }
+
+    reqLength += (int32_t)(pDest - dest);
+    if(pDestLength) {
+        *pDestLength = reqLength;
+    }
+    if(pNumSubstitutions != nullptr) {
+        *pNumSubstitutions = numSubstitutions;
+    }
+
+    /* Terminate the buffer */
+    u_terminateUChar32s(dest, destCapacity, reqLength, pErrorCode);
+
+    return dest;
+}
+
+U_CAPI UChar32* U_EXPORT2 
+u_strToUTF32(UChar32 *dest, 
+             int32_t destCapacity,
+             int32_t *pDestLength,
+             const char16_t *src,
+             int32_t srcLength,
+             UErrorCode *pErrorCode) {
+    return u_strToUTF32WithSub(
+            dest, destCapacity, pDestLength,
+            src, srcLength,
+            U_SENTINEL, nullptr,
+            pErrorCode);
+}
+
+U_CAPI char16_t* U_EXPORT2
+u_strFromUTF8WithSub(char16_t *dest,
+              int32_t destCapacity,
+              int32_t *pDestLength,
+              const char* src,
+              int32_t srcLength,
+              UChar32 subchar, int32_t *pNumSubstitutions,
+              UErrorCode *pErrorCode){
+    /* args check */
+    if(U_FAILURE(*pErrorCode)) {
+        return nullptr;
+    }
+    if( (src==nullptr && srcLength!=0) || srcLength < -1 ||
+        (destCapacity<0) || (dest == nullptr && destCapacity > 0) ||
+        subchar > 0x10ffff || U_IS_SURROGATE(subchar)
+    ) {
+        *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        return nullptr;
+    }
+
+    if(pNumSubstitutions!=nullptr) {
+        *pNumSubstitutions=0;
+    }
+    char16_t *pDest = dest;
+    char16_t *pDestLimit = dest+destCapacity;
+    int32_t reqLength = 0;
+    int32_t numSubstitutions=0;
+
+    /*
+     * Inline processing of UTF-8 byte sequences:
+     *
+     * Byte sequences for the most common characters are handled inline in
+     * the conversion loops. In order to reduce the path lengths for those
+     * characters, the tests are arranged in a kind of binary search.
+     * ASCII (<=0x7f) is checked first, followed by the dividing point
+     * between 2- and 3-byte sequences (0xe0).
+     * The 3-byte branch is tested first to speed up CJK text.
+     * The compiler should combine the subtractions for the two tests for 0xe0.
+     * Each branch then tests for the other end of its range.
+     */
+
+    if(srcLength < 0){
+        /*
+         * Transform a NUL-terminated string.
+         * The code explicitly checks for NULs only in the lead byte position.
+         * A NUL byte in the trail byte position fails the trail byte range check anyway.
+         */
+        int32_t i;
+        UChar32 c;
+        for(i = 0; (c = (uint8_t)src[i]) != 0 && (pDest < pDestLimit);) {
+            // modified copy of U8_NEXT()
+            ++i;
+            if(U8_IS_SINGLE(c)) {
+                *pDest++=(char16_t)c;
+            } else {
+                uint8_t __t1, __t2;
+                if( /* handle U+0800..U+FFFF inline */
+                        (0xe0<=(c) && (c)<0xf0) &&
+                        U8_IS_VALID_LEAD3_AND_T1((c), src[i]) &&
+                        (__t2=src[(i)+1]-0x80)<=0x3f) {
+                    *pDest++ = (((c)&0xf)<<12)|((src[i]&0x3f)<<6)|__t2;
+                    i+=2;
+                } else if( /* handle U+0080..U+07FF inline */
+                        ((c)<0xe0 && (c)>=0xc2) &&
+                        (__t1=src[i]-0x80)<=0x3f) {
+                    *pDest++ = (((c)&0x1f)<<6)|__t1;
+                    ++(i);
+                } else {
+                    /* function call for "complicated" and error cases */
+                    (c)=utf8_nextCharSafeBody((const uint8_t *)src, &(i), -1, c, -1);
+                    if(c<0 && (++numSubstitutions, c = subchar) < 0) {
+                        *pErrorCode = U_INVALID_CHAR_FOUND;
+                        return nullptr;
+                    } else if(c<=0xFFFF) {
+                        *(pDest++)=(char16_t)c;
+                    } else {
+                        *(pDest++)=U16_LEAD(c);
+                        if(pDest<pDestLimit) {
+                            *(pDest++)=U16_TRAIL(c);
+                        } else {
+                            reqLength++;
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+
+        /* Pre-flight the rest of the string. */
+        while((c = (uint8_t)src[i]) != 0) {
+            // modified copy of U8_NEXT()
+            ++i;
+            if(U8_IS_SINGLE(c)) {
+                ++reqLength;
+            } else {
+                uint8_t __t1, __t2;
+                if( /* handle U+0800..U+FFFF inline */
+                        (0xe0<=(c) && (c)<0xf0) &&
+                        U8_IS_VALID_LEAD3_AND_T1((c), src[i]) &&
+                        (__t2=src[(i)+1]-0x80)<=0x3f) {
+                    ++reqLength;
+                    i+=2;
+                } else if( /* handle U+0080..U+07FF inline */
+                        ((c)<0xe0 && (c)>=0xc2) &&
+                        (__t1=src[i]-0x80)<=0x3f) {
+                    ++reqLength;
+                    ++(i);
+                } else {
+                    /* function call for "complicated" and error cases */
+                    (c)=utf8_nextCharSafeBody((const uint8_t *)src, &(i), -1, c, -1);
+                    if(c<0 && (++numSubstitutions, c = subchar) < 0) {
+                        *pErrorCode = U_INVALID_CHAR_FOUND;
+                        return nullptr;
+                    }
+                    reqLength += U16_LENGTH(c);
+                }
+            }
+        }
+    } else /* srcLength >= 0 */ {
+        /* Faster loop without ongoing checking for srcLength and pDestLimit. */
+        int32_t i = 0;
+        UChar32 c;
+        for(;;) {
+            /*
+             * Each iteration of the inner loop progresses by at most 3 UTF-8
+             * bytes and one char16_t, for most characters.
+             * For supplementary code points (4 & 2), which are rare,
+             * there is an additional adjustment.
+             */
+            int32_t count = (int32_t)(pDestLimit - pDest);
+            int32_t count2 = (srcLength - i) / 3;
+            if(count > count2) {
+                count = count2; /* min(remaining dest, remaining src/3) */
+            }
+            if(count < 3) {
+                /*
+                 * Too much overhead if we get near the end of the string,
+                 * continue with the next loop.
+                 */
+                break;
+            }
+
+            do {
+                // modified copy of U8_NEXT()
+                c = (uint8_t)src[i++];
+                if(U8_IS_SINGLE(c)) {
+                    *pDest++=(char16_t)c;
+                } else {
+                    uint8_t __t1, __t2;
+                    if( /* handle U+0800..U+FFFF inline */
+                            (0xe0<=(c) && (c)<0xf0) &&
+                            ((i)+1)<srcLength &&
+                            U8_IS_VALID_LEAD3_AND_T1((c), src[i]) &&
+                            (__t2=src[(i)+1]-0x80)<=0x3f) {
+                        *pDest++ = (((c)&0xf)<<12)|((src[i]&0x3f)<<6)|__t2;
+                        i+=2;
+                    } else if( /* handle U+0080..U+07FF inline */
+                            ((c)<0xe0 && (c)>=0xc2) &&
+                            ((i)!=srcLength) &&
+                            (__t1=src[i]-0x80)<=0x3f) {
+                        *pDest++ = (((c)&0x1f)<<6)|__t1;
+                        ++(i);
+                    } else {
+                        if(c >= 0xf0 || subchar > 0xffff) {
+                            // We may read up to four bytes and write up to two UChars,
+                            // which we didn't account for with computing count,
+                            // so we adjust it here.
+                            if(--count == 0) {
+                                --i;  // back out byte c
+                                break;
+                            }
+                        }
+
+                        /* function call for "complicated" and error cases */
+                        (c)=utf8_nextCharSafeBody((const uint8_t *)src, &(i), srcLength, c, -1);
+                        if(c<0 && (++numSubstitutions, c = subchar) < 0) {
+                            *pErrorCode = U_INVALID_CHAR_FOUND;
+                            return nullptr;
+                        } else if(c<=0xFFFF) {
+                            *(pDest++)=(char16_t)c;
+                        } else {
+                            *(pDest++)=U16_LEAD(c);
+                            *(pDest++)=U16_TRAIL(c);
+                        }
+                    }
+                }
+            } while(--count > 0);
+        }
+
+        while(i < srcLength && (pDest < pDestLimit)) {
+            // modified copy of U8_NEXT()
+            c = (uint8_t)src[i++];
+            if(U8_IS_SINGLE(c)) {
+                *pDest++=(char16_t)c;
+            } else {
+                uint8_t __t1, __t2;
+                if( /* handle U+0800..U+FFFF inline */
+                        (0xe0<=(c) && (c)<0xf0) &&
+                        ((i)+1)<srcLength &&
+                        U8_IS_VALID_LEAD3_AND_T1((c), src[i]) &&
+                        (__t2=src[(i)+1]-0x80)<=0x3f) {
+                    *pDest++ = (((c)&0xf)<<12)|((src[i]&0x3f)<<6)|__t2;
+                    i+=2;
+                } else if( /* handle U+0080..U+07FF inline */
+                        ((c)<0xe0 && (c)>=0xc2) &&
+                        ((i)!=srcLength) &&
+                        (__t1=src[i]-0x80)<=0x3f) {
+                    *pDest++ = (((c)&0x1f)<<6)|__t1;
+                    ++(i);
+                } else {
+                    /* function call for "complicated" and error cases */
+                    (c)=utf8_nextCharSafeBody((const uint8_t *)src, &(i), srcLength, c, -1);
+                    if(c<0 && (++numSubstitutions, c = subchar) < 0) {
+                        *pErrorCode = U_INVALID_CHAR_FOUND;
+                        return nullptr;
+                    } else if(c<=0xFFFF) {
+                        *(pDest++)=(char16_t)c;
+                    } else {
+                        *(pDest++)=U16_LEAD(c);
+                        if(pDest<pDestLimit) {
+                            *(pDest++)=U16_TRAIL(c);
+                        } else {
+                            reqLength++;
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+
+        /* Pre-flight the rest of the string. */
+        while(i < srcLength) {
+            // modified copy of U8_NEXT()
+            c = (uint8_t)src[i++];
+            if(U8_IS_SINGLE(c)) {
+                ++reqLength;
+            } else {
+                uint8_t __t1, __t2;
+                if( /* handle U+0800..U+FFFF inline */
+                        (0xe0<=(c) && (c)<0xf0) &&
+                        ((i)+1)<srcLength &&
+                        U8_IS_VALID_LEAD3_AND_T1((c), src[i]) &&
+                        (__t2=src[(i)+1]-0x80)<=0x3f) {
+                    ++reqLength;
+                    i+=2;
+                } else if( /* handle U+0080..U+07FF inline */
+                        ((c)<0xe0 && (c)>=0xc2) &&
+                        ((i)!=srcLength) &&
+                        (__t1=src[i]-0x80)<=0x3f) {
+                    ++reqLength;
+                    ++(i);
+                } else {
+                    /* function call for "complicated" and error cases */
+                    (c)=utf8_nextCharSafeBody((const uint8_t *)src, &(i), srcLength, c, -1);
+                    if(c<0 && (++numSubstitutions, c = subchar) < 0) {
+                        *pErrorCode = U_INVALID_CHAR_FOUND;
+                        return nullptr;
+                    }
+                    reqLength += U16_LENGTH(c);
+                }
+            }
+        }
+    }
+
+    reqLength+=(int32_t)(pDest - dest);
+
+    if(pNumSubstitutions!=nullptr) {
+        *pNumSubstitutions=numSubstitutions;
+    }
+
+    if(pDestLength){
+        *pDestLength = reqLength;
+    }
+
+    /* Terminate the buffer */
+    u_terminateUChars(dest,destCapacity,reqLength,pErrorCode);
+
+    return dest;
+}
+
+U_CAPI char16_t* U_EXPORT2
+u_strFromUTF8(char16_t *dest,
+              int32_t destCapacity,
+              int32_t *pDestLength,
+              const char* src,
+              int32_t srcLength,
+              UErrorCode *pErrorCode){
+    return u_strFromUTF8WithSub(
+            dest, destCapacity, pDestLength,
+            src, srcLength,
+            U_SENTINEL, nullptr,
+            pErrorCode);
+}
+
+U_CAPI char16_t * U_EXPORT2
+u_strFromUTF8Lenient(char16_t *dest,
+                     int32_t destCapacity,
+                     int32_t *pDestLength,
+                     const char *src,
+                     int32_t srcLength,
+                     UErrorCode *pErrorCode) {
+    char16_t *pDest = dest;
+    UChar32 ch;
+    int32_t reqLength = 0;
+    uint8_t* pSrc = (uint8_t*) src;
+
+    /* args check */
+    if(U_FAILURE(*pErrorCode)){
+        return nullptr;
+    }
+        
+    if( (src==nullptr && srcLength!=0) || srcLength < -1 ||
+        (destCapacity<0) || (dest == nullptr && destCapacity > 0)
+    ) {
+        *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        return nullptr;
+    }
+
+    if(srcLength < 0) {
+        /* Transform a NUL-terminated string. */
+        char16_t *pDestLimit = (dest!=nullptr)?(dest+destCapacity):nullptr;
+        uint8_t t1, t2, t3; /* trail bytes */
+
+        while(((ch = *pSrc) != 0) && (pDest < pDestLimit)) {
+            if(ch < 0xc0) {
+                /*
+                 * ASCII, or a trail byte in lead position which is treated like
+                 * a single-byte sequence for better character boundary
+                 * resynchronization after illegal sequences.
+                 */
+                *pDest++=(char16_t)ch;
+                ++pSrc;
+                continue;
+            } else if(ch < 0xe0) { /* U+0080..U+07FF */
+                if((t1 = pSrc[1]) != 0) {
+                    /* 0x3080 = (0xc0 << 6) + 0x80 */
+                    *pDest++ = (char16_t)((ch << 6) + t1 - 0x3080);
+                    pSrc += 2;
+                    continue;
+                }
+            } else if(ch < 0xf0) { /* U+0800..U+FFFF */
+                if((t1 = pSrc[1]) != 0 && (t2 = pSrc[2]) != 0) {
+                    /* no need for (ch & 0xf) because the upper bits are truncated after <<12 in the cast to (char16_t) */
+                    /* 0x2080 = (0x80 << 6) + 0x80 */
+                    *pDest++ = (char16_t)((ch << 12) + (t1 << 6) + t2 - 0x2080);
+                    pSrc += 3;
+                    continue;
+                }
+            } else /* f0..f4 */ { /* U+10000..U+10FFFF */
+                if((t1 = pSrc[1]) != 0 && (t2 = pSrc[2]) != 0 && (t3 = pSrc[3]) != 0) {
+                    pSrc += 4;
+                    /* 0x3c82080 = (0xf0 << 18) + (0x80 << 12) + (0x80 << 6) + 0x80 */
+                    ch = (ch << 18) + (t1 << 12) + (t2 << 6) + t3 - 0x3c82080;
+                    *(pDest++) = U16_LEAD(ch);
+                    if(pDest < pDestLimit) {
+                        *(pDest++) = U16_TRAIL(ch);
+                    } else {
+                        reqLength = 1;
+                        break;
+                    }
+                    continue;
+                }
+            }
+
+            /* truncated character at the end */
+            *pDest++ = 0xfffd;
+            while(*++pSrc != 0) {}
+            break;
+        }
+
+        /* Pre-flight the rest of the string. */
+        while((ch = *pSrc) != 0) {
+            if(ch < 0xc0) {
+                /*
+                 * ASCII, or a trail byte in lead position which is treated like
+                 * a single-byte sequence for better character boundary
+                 * resynchronization after illegal sequences.
+                 */
+                ++reqLength;
+                ++pSrc;
+                continue;
+            } else if(ch < 0xe0) { /* U+0080..U+07FF */
+                if(pSrc[1] != 0) {
+                    ++reqLength;
+                    pSrc += 2;
+                    continue;
+                }
+            } else if(ch < 0xf0) { /* U+0800..U+FFFF */
+                if(pSrc[1] != 0 && pSrc[2] != 0) {
+                    ++reqLength;
+                    pSrc += 3;
+                    continue;
+                }
+            } else /* f0..f4 */ { /* U+10000..U+10FFFF */
+                if(pSrc[1] != 0 && pSrc[2] != 0 && pSrc[3] != 0) {
+                    reqLength += 2;
+                    pSrc += 4;
+                    continue;
+                }
+            }
+
+            /* truncated character at the end */
+            ++reqLength;
+            break;
+        }
+    } else /* srcLength >= 0 */ {
+      const uint8_t *pSrcLimit = (pSrc!=nullptr)?(pSrc + srcLength):nullptr;
+
+        /*
+         * This function requires that if srcLength is given, then it must be
+         * destCapatity >= srcLength so that we need not check for
+         * destination buffer overflow in the loop.
+         */
+        if(destCapacity < srcLength) {
+            if(pDestLength != nullptr) {
+                *pDestLength = srcLength; /* this likely overestimates the true destLength! */
+            }
+            *pErrorCode = U_BUFFER_OVERFLOW_ERROR;
+            return nullptr;
+        }
+
+        if((pSrcLimit - pSrc) >= 4) {
+            pSrcLimit -= 3; /* temporarily reduce pSrcLimit */
+
+            /* in this loop, we can always access at least 4 bytes, up to pSrc+3 */
+            do {
+                ch = *pSrc++;
+                if(ch < 0xc0) {
+                    /*
+                     * ASCII, or a trail byte in lead position which is treated like
+                     * a single-byte sequence for better character boundary
+                     * resynchronization after illegal sequences.
+                     */
+                    *pDest++=(char16_t)ch;
+                } else if(ch < 0xe0) { /* U+0080..U+07FF */
+                    /* 0x3080 = (0xc0 << 6) + 0x80 */
+                    *pDest++ = (char16_t)((ch << 6) + *pSrc++ - 0x3080);
+                } else if(ch < 0xf0) { /* U+0800..U+FFFF */
+                    /* no need for (ch & 0xf) because the upper bits are truncated after <<12 in the cast to (char16_t) */
+                    /* 0x2080 = (0x80 << 6) + 0x80 */
+                    ch = (ch << 12) + (*pSrc++ << 6);
+                    *pDest++ = (char16_t)(ch + *pSrc++ - 0x2080);
+                } else /* f0..f4 */ { /* U+10000..U+10FFFF */
+                    /* 0x3c82080 = (0xf0 << 18) + (0x80 << 12) + (0x80 << 6) + 0x80 */
+                    ch = (ch << 18) + (*pSrc++ << 12);
+                    ch += *pSrc++ << 6;
+                    ch += *pSrc++ - 0x3c82080;
+                    *(pDest++) = U16_LEAD(ch);
+                    *(pDest++) = U16_TRAIL(ch);
+                }
+            } while(pSrc < pSrcLimit);
+
+            pSrcLimit += 3; /* restore original pSrcLimit */
+        }
+
+        while(pSrc < pSrcLimit) {
+            ch = *pSrc++;
+            if(ch < 0xc0) {
+                /*
+                 * ASCII, or a trail byte in lead position which is treated like
+                 * a single-byte sequence for better character boundary
+                 * resynchronization after illegal sequences.
+                 */
+                *pDest++=(char16_t)ch;
+                continue;
+            } else if(ch < 0xe0) { /* U+0080..U+07FF */
+                if(pSrc < pSrcLimit) {
+                    /* 0x3080 = (0xc0 << 6) + 0x80 */
+                    *pDest++ = (char16_t)((ch << 6) + *pSrc++ - 0x3080);
+                    continue;
+                }
+            } else if(ch < 0xf0) { /* U+0800..U+FFFF */
+                if((pSrcLimit - pSrc) >= 2) {
+                    /* no need for (ch & 0xf) because the upper bits are truncated after <<12 in the cast to (char16_t) */
+                    /* 0x2080 = (0x80 << 6) + 0x80 */
+                    ch = (ch << 12) + (*pSrc++ << 6);
+                    *pDest++ = (char16_t)(ch + *pSrc++ - 0x2080);
+                    pSrc += 3;
+                    continue;
+                }
+            } else /* f0..f4 */ { /* U+10000..U+10FFFF */
+                if((pSrcLimit - pSrc) >= 3) {
+                    /* 0x3c82080 = (0xf0 << 18) + (0x80 << 12) + (0x80 << 6) + 0x80 */
+                    ch = (ch << 18) + (*pSrc++ << 12);
+                    ch += *pSrc++ << 6;
+                    ch += *pSrc++ - 0x3c82080;
+                    *(pDest++) = U16_LEAD(ch);
+                    *(pDest++) = U16_TRAIL(ch);
+                    pSrc += 4;
+                    continue;
+                }
+            }
+
+            /* truncated character at the end */
+            *pDest++ = 0xfffd;
+            break;
+        }
+    }
+
+    reqLength+=(int32_t)(pDest - dest);
+
+    if(pDestLength){
+        *pDestLength = reqLength;
+    }
+
+    /* Terminate the buffer */
+    u_terminateUChars(dest,destCapacity,reqLength,pErrorCode);
+
+    return dest;
+}
+
+static inline uint8_t *
+_appendUTF8(uint8_t *pDest, UChar32 c) {
+    /* it is 0<=c<=0x10ffff and not a surrogate if called by a validating function */
+    if((c)<=0x7f) {
+        *pDest++=(uint8_t)c;
+    } else if(c<=0x7ff) {
+        *pDest++=(uint8_t)((c>>6)|0xc0);
+        *pDest++=(uint8_t)((c&0x3f)|0x80);
+    } else if(c<=0xffff) {
+        *pDest++=(uint8_t)((c>>12)|0xe0);
+        *pDest++=(uint8_t)(((c>>6)&0x3f)|0x80);
+        *pDest++=(uint8_t)(((c)&0x3f)|0x80);
+    } else /* if((uint32_t)(c)<=0x10ffff) */ {
+        *pDest++=(uint8_t)(((c)>>18)|0xf0);
+        *pDest++=(uint8_t)((((c)>>12)&0x3f)|0x80);
+        *pDest++=(uint8_t)((((c)>>6)&0x3f)|0x80);
+        *pDest++=(uint8_t)(((c)&0x3f)|0x80);
+    }
+    return pDest;
+}
+
+   
+U_CAPI char* U_EXPORT2 
+u_strToUTF8WithSub(char *dest,
+            int32_t destCapacity,
+            int32_t *pDestLength,
+            const char16_t *pSrc,
+            int32_t srcLength,
+            UChar32 subchar, int32_t *pNumSubstitutions,
+            UErrorCode *pErrorCode){
+    int32_t reqLength=0;
+    uint32_t ch=0,ch2=0;
+    uint8_t *pDest = (uint8_t *)dest;
+    uint8_t *pDestLimit = (pDest!=nullptr)?(pDest + destCapacity):nullptr;
+    int32_t numSubstitutions;
+
+    /* args check */
+    if(U_FAILURE(*pErrorCode)){
+        return nullptr;
+    }
+        
+    if( (pSrc==nullptr && srcLength!=0) || srcLength < -1 ||
+        (destCapacity<0) || (dest == nullptr && destCapacity > 0) ||
+        subchar > 0x10ffff || U_IS_SURROGATE(subchar)
+    ) {
+        *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        return nullptr;
+    }
+
+    if(pNumSubstitutions!=nullptr) {
+        *pNumSubstitutions=0;
+    }
+    numSubstitutions=0;
+
+    if(srcLength==-1) {
+        while((ch=*pSrc)!=0) {
+            ++pSrc;
+            if(ch <= 0x7f) {
+                if(pDest<pDestLimit) {
+                    *pDest++ = (uint8_t)ch;
+                } else {
+                    reqLength = 1;
+                    break;
+                }
+            } else if(ch <= 0x7ff) {
+                if((pDestLimit - pDest) >= 2) {
+                    *pDest++=(uint8_t)((ch>>6)|0xc0);
+                    *pDest++=(uint8_t)((ch&0x3f)|0x80);
+                } else {
+                    reqLength = 2;
+                    break;
+                }
+            } else if(ch <= 0xd7ff || ch >= 0xe000) {
+                if((pDestLimit - pDest) >= 3) {
+                    *pDest++=(uint8_t)((ch>>12)|0xe0);
+                    *pDest++=(uint8_t)(((ch>>6)&0x3f)|0x80);
+                    *pDest++=(uint8_t)((ch&0x3f)|0x80);
+                } else {
+                    reqLength = 3;
+                    break;
+                }
+            } else /* ch is a surrogate */ {
+                int32_t length;
+
+                /*need not check for NUL because NUL fails U16_IS_TRAIL() anyway*/
+                if(U16_IS_SURROGATE_LEAD(ch) && U16_IS_TRAIL(ch2=*pSrc)) { 
+                    ++pSrc;
+                    ch=U16_GET_SUPPLEMENTARY(ch, ch2);
+                } else if(subchar>=0) {
+                    ch=subchar;
+                    ++numSubstitutions;
+                } else {
+                    /* Unicode 3.2 forbids surrogate code points in UTF-8 */
+                    *pErrorCode = U_INVALID_CHAR_FOUND;
+                    return nullptr;
+                }
+
+                length = U8_LENGTH(ch);
+                if((pDestLimit - pDest) >= length) {
+                    /* convert and append*/
+                    pDest=_appendUTF8(pDest, ch);
+                } else {
+                    reqLength = length;
+                    break;
+                }
+            }
+        }
+        while((ch=*pSrc++)!=0) {
+            if(ch<=0x7f) {
+                ++reqLength;
+            } else if(ch<=0x7ff) {
+                reqLength+=2;
+            } else if(!U16_IS_SURROGATE(ch)) {
+                reqLength+=3;
+            } else if(U16_IS_SURROGATE_LEAD(ch) && U16_IS_TRAIL(ch2=*pSrc)) {
+                ++pSrc;
+                reqLength+=4;
+            } else if(subchar>=0) {
+                reqLength+=U8_LENGTH(subchar);
+                ++numSubstitutions;
+            } else {
+                /* Unicode 3.2 forbids surrogate code points in UTF-8 */
+                *pErrorCode = U_INVALID_CHAR_FOUND;
+                return nullptr;
+            }
+        }
+    } else {
+        const char16_t *pSrcLimit = (pSrc!=nullptr)?(pSrc+srcLength):nullptr;
+        int32_t count;
+
+        /* Faster loop without ongoing checking for pSrcLimit and pDestLimit. */
+        for(;;) {
+            /*
+             * Each iteration of the inner loop progresses by at most 3 UTF-8
+             * bytes and one char16_t, for most characters.
+             * For supplementary code points (4 & 2), which are rare,
+             * there is an additional adjustment.
+             */
+            count = (int32_t)((pDestLimit - pDest) / 3);
+            srcLength = (int32_t)(pSrcLimit - pSrc);
+            if(count > srcLength) {
+                count = srcLength; /* min(remaining dest/3, remaining src) */
+            }
+            if(count < 3) {
+                /*
+                 * Too much overhead if we get near the end of the string,
+                 * continue with the next loop.
+                 */
+                break;
+            }
+            do {
+                ch=*pSrc++;
+                if(ch <= 0x7f) {
+                    *pDest++ = (uint8_t)ch;
+                } else if(ch <= 0x7ff) {
+                    *pDest++=(uint8_t)((ch>>6)|0xc0);
+                    *pDest++=(uint8_t)((ch&0x3f)|0x80);
+                } else if(ch <= 0xd7ff || ch >= 0xe000) {
+                    *pDest++=(uint8_t)((ch>>12)|0xe0);
+                    *pDest++=(uint8_t)(((ch>>6)&0x3f)|0x80);
+                    *pDest++=(uint8_t)((ch&0x3f)|0x80);
+                } else /* ch is a surrogate */ {
+                    /*
+                     * We will read two UChars and probably output four bytes,
+                     * which we didn't account for with computing count,
+                     * so we adjust it here.
+                     */
+                    if(--count == 0) {
+                        --pSrc; /* undo ch=*pSrc++ for the lead surrogate */
+                        break;  /* recompute count */
+                    }
+
+                    if(U16_IS_SURROGATE_LEAD(ch) && U16_IS_TRAIL(ch2=*pSrc)) { 
+                        ++pSrc;
+                        ch=U16_GET_SUPPLEMENTARY(ch, ch2);
+
+                        /* writing 4 bytes per 2 UChars is ok */
+                        *pDest++=(uint8_t)((ch>>18)|0xf0);
+                        *pDest++=(uint8_t)(((ch>>12)&0x3f)|0x80);
+                        *pDest++=(uint8_t)(((ch>>6)&0x3f)|0x80);
+                        *pDest++=(uint8_t)((ch&0x3f)|0x80);
+                    } else  {
+                        /* Unicode 3.2 forbids surrogate code points in UTF-8 */
+                        if(subchar>=0) {
+                            ch=subchar;
+                            ++numSubstitutions;
+                        } else {
+                            *pErrorCode = U_INVALID_CHAR_FOUND;
+                            return nullptr;
+                        }
+
+                        /* convert and append*/
+                        pDest=_appendUTF8(pDest, ch);
+                    }
+                }
+            } while(--count > 0);
+        }
+
+        while(pSrc<pSrcLimit) {
+            ch=*pSrc++;
+            if(ch <= 0x7f) {
+                if(pDest<pDestLimit) {
+                    *pDest++ = (uint8_t)ch;
+                } else {
+                    reqLength = 1;
+                    break;
+                }
+            } else if(ch <= 0x7ff) {
+                if((pDestLimit - pDest) >= 2) {
+                    *pDest++=(uint8_t)((ch>>6)|0xc0);
+                    *pDest++=(uint8_t)((ch&0x3f)|0x80);
+                } else {
+                    reqLength = 2;
+                    break;
+                }
+            } else if(ch <= 0xd7ff || ch >= 0xe000) {
+                if((pDestLimit - pDest) >= 3) {
+                    *pDest++=(uint8_t)((ch>>12)|0xe0);
+                    *pDest++=(uint8_t)(((ch>>6)&0x3f)|0x80);
+                    *pDest++=(uint8_t)((ch&0x3f)|0x80);
+                } else {
+                    reqLength = 3;
+                    break;
+                }
+            } else /* ch is a surrogate */ {
+                int32_t length;
+
+                if(U16_IS_SURROGATE_LEAD(ch) && pSrc<pSrcLimit && U16_IS_TRAIL(ch2=*pSrc)) { 
+                    ++pSrc;
+                    ch=U16_GET_SUPPLEMENTARY(ch, ch2);
+                } else if(subchar>=0) {
+                    ch=subchar;
+                    ++numSubstitutions;
+                } else {
+                    /* Unicode 3.2 forbids surrogate code points in UTF-8 */
+                    *pErrorCode = U_INVALID_CHAR_FOUND;
+                    return nullptr;
+                }
+
+                length = U8_LENGTH(ch);
+                if((pDestLimit - pDest) >= length) {
+                    /* convert and append*/
+                    pDest=_appendUTF8(pDest, ch);
+                } else {
+                    reqLength = length;
+                    break;
+                }
+            }
+        }
+        while(pSrc<pSrcLimit) {
+            ch=*pSrc++;
+            if(ch<=0x7f) {
+                ++reqLength;
+            } else if(ch<=0x7ff) {
+                reqLength+=2;
+            } else if(!U16_IS_SURROGATE(ch)) {
+                reqLength+=3;
+            } else if(U16_IS_SURROGATE_LEAD(ch) && pSrc<pSrcLimit && U16_IS_TRAIL(ch2=*pSrc)) {
+                ++pSrc;
+                reqLength+=4;
+            } else if(subchar>=0) {
+                reqLength+=U8_LENGTH(subchar);
+                ++numSubstitutions;
+            } else {
+                /* Unicode 3.2 forbids surrogate code points in UTF-8 */
+                *pErrorCode = U_INVALID_CHAR_FOUND;
+                return nullptr;
+            }
+        }
+    }
+
+    reqLength+=(int32_t)(pDest - (uint8_t *)dest);
+
+    if(pNumSubstitutions!=nullptr) {
+        *pNumSubstitutions=numSubstitutions;
+    }
+
+    if(pDestLength){
+        *pDestLength = reqLength;
+    }
+
+    /* Terminate the buffer */
+    u_terminateChars(dest, destCapacity, reqLength, pErrorCode);
+    return dest;
+}
+
+U_CAPI char* U_EXPORT2 
+u_strToUTF8(char *dest,
+            int32_t destCapacity,
+            int32_t *pDestLength,
+            const char16_t *pSrc,
+            int32_t srcLength,
+            UErrorCode *pErrorCode){
+    return u_strToUTF8WithSub(
+            dest, destCapacity, pDestLength,
+            pSrc, srcLength,
+            U_SENTINEL, nullptr,
+            pErrorCode);
+}
+
+U_CAPI char16_t* U_EXPORT2
+u_strFromJavaModifiedUTF8WithSub(
+        char16_t *dest,
+        int32_t destCapacity,
+        int32_t *pDestLength,
+        const char *src,
+        int32_t srcLength,
+        UChar32 subchar, int32_t *pNumSubstitutions,
+        UErrorCode *pErrorCode) {
+    /* args check */
+    if(U_FAILURE(*pErrorCode)) {
+        return nullptr;
+    }
+    if( (src==nullptr && srcLength!=0) || srcLength < -1 ||
+        (dest==nullptr && destCapacity!=0) || destCapacity<0 ||
+        subchar > 0x10ffff || U_IS_SURROGATE(subchar)
+    ) {
+        *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        return nullptr;
+    }
+
+    if(pNumSubstitutions!=nullptr) {
+        *pNumSubstitutions=0;
+    }
+    char16_t *pDest = dest;
+    char16_t *pDestLimit = dest+destCapacity;
+    int32_t reqLength = 0;
+    int32_t numSubstitutions=0;
+
+    if(srcLength < 0) {
+        /*
+         * Transform a NUL-terminated ASCII string.
+         * Handle non-ASCII strings with slower code.
+         */
+        UChar32 c;
+        while(((c = (uint8_t)*src) != 0) && c <= 0x7f && (pDest < pDestLimit)) {
+            *pDest++=(char16_t)c;
+            ++src;
+        }
+        if(c == 0) {
+            reqLength=(int32_t)(pDest - dest);
+            if(pDestLength) {
+                *pDestLength = reqLength;
+            }
+
+            /* Terminate the buffer */
+            u_terminateUChars(dest, destCapacity, reqLength, pErrorCode);
+            return dest;
+        }
+        srcLength = static_cast<int32_t>(uprv_strlen(src));
+    }
+
+    /* Faster loop without ongoing checking for srcLength and pDestLimit. */
+    UChar32 ch;
+    uint8_t t1, t2;
+    int32_t i = 0;
+    for(;;) {
+        int32_t count = (int32_t)(pDestLimit - pDest);
+        int32_t count2 = srcLength - i;
+        if(count >= count2 && srcLength > 0 && U8_IS_SINGLE(*src)) {
+            /* fast ASCII loop */
+            int32_t start = i;
+            uint8_t b;
+            while(i < srcLength && U8_IS_SINGLE(b = src[i])) {
+                *pDest++=b;
+                ++i;
+            }
+            int32_t delta = i - start;
+            count -= delta;
+            count2 -= delta;
+        }
+        /*
+         * Each iteration of the inner loop progresses by at most 3 UTF-8
+         * bytes and one char16_t.
+         */
+        if(subchar > 0xFFFF) {
+            break;
+        }
+        count2 /= 3;
+        if(count > count2) {
+            count = count2; /* min(remaining dest, remaining src/3) */
+        }
+        if(count < 3) {
+            /*
+             * Too much overhead if we get near the end of the string,
+             * continue with the next loop.
+             */
+            break;
+        }
+        do {
+            ch = (uint8_t)src[i++];
+            if(U8_IS_SINGLE(ch)) {
+                *pDest++=(char16_t)ch;
+            } else {
+                if(ch >= 0xe0) {
+                    if( /* handle U+0000..U+FFFF inline */
+                        ch <= 0xef &&
+                        (t1 = (uint8_t)(src[i] - 0x80)) <= 0x3f &&
+                        (t2 = (uint8_t)(src[i+1] - 0x80)) <= 0x3f
+                    ) {
+                        /* no need for (ch & 0xf) because the upper bits are truncated after <<12 in the cast to (char16_t) */
+                        *pDest++ = (char16_t)((ch << 12) | (t1 << 6) | t2);
+                        i += 2;
+                        continue;
+                    }
+                } else {
+                    if( /* handle U+0000..U+07FF inline */
+                        ch >= 0xc0 &&
+                        (t1 = (uint8_t)(src[i] - 0x80)) <= 0x3f
+                    ) {
+                        *pDest++ = (char16_t)(((ch & 0x1f) << 6) | t1);
+                        ++i;
+                        continue;
+                    }
+                }
+
+                if(subchar < 0) {
+                    *pErrorCode = U_INVALID_CHAR_FOUND;
+                    return nullptr;
+                } else if(subchar > 0xffff && --count == 0) {
+                    /*
+                     * We need to write two UChars, adjusted count for that,
+                     * and ran out of space.
+                     */
+                    --i;  // back out byte ch
+                    break;
+                } else {
+                    /* function call for error cases */
+                    utf8_nextCharSafeBody((const uint8_t *)src, &(i), srcLength, ch, -1);
+                    ++numSubstitutions;
+                    *(pDest++)=(char16_t)subchar;
+                }
+            }
+        } while(--count > 0);
+    }
+
+    while(i < srcLength && (pDest < pDestLimit)) {
+        ch = (uint8_t)src[i++];
+        if(U8_IS_SINGLE(ch)){
+            *pDest++=(char16_t)ch;
+        } else {
+            if(ch >= 0xe0) {
+                if( /* handle U+0000..U+FFFF inline */
+                    ch <= 0xef &&
+                    (i+1) < srcLength &&
+                    (t1 = (uint8_t)(src[i] - 0x80)) <= 0x3f &&
+                    (t2 = (uint8_t)(src[i+1] - 0x80)) <= 0x3f
+                ) {
+                    /* no need for (ch & 0xf) because the upper bits are truncated after <<12 in the cast to (char16_t) */
+                    *pDest++ = (char16_t)((ch << 12) | (t1 << 6) | t2);
+                    i += 2;
+                    continue;
+                }
+            } else {
+                if( /* handle U+0000..U+07FF inline */
+                    ch >= 0xc0 &&
+                    i < srcLength &&
+                    (t1 = (uint8_t)(src[i] - 0x80)) <= 0x3f
+                ) {
+                    *pDest++ = (char16_t)(((ch & 0x1f) << 6) | t1);
+                    ++i;
+                    continue;
+                }
+            }
+
+            if(subchar < 0) {
+                *pErrorCode = U_INVALID_CHAR_FOUND;
+                return nullptr;
+            } else {
+                /* function call for error cases */
+                utf8_nextCharSafeBody((const uint8_t *)src, &(i), srcLength, ch, -1);
+                ++numSubstitutions;
+                if(subchar<=0xFFFF) {
+                    *(pDest++)=(char16_t)subchar;
+                } else {
+                    *(pDest++)=U16_LEAD(subchar);
+                    if(pDest<pDestLimit) {
+                        *(pDest++)=U16_TRAIL(subchar);
+                    } else {
+                        reqLength++;
+                        break;
+                    }
+                }
+            }
+        }
+    }
+
+    /* Pre-flight the rest of the string. */
+    while(i < srcLength) {
+        ch = (uint8_t)src[i++];
+        if(U8_IS_SINGLE(ch)) {
+            reqLength++;
+        } else {
+            if(ch >= 0xe0) {
+                if( /* handle U+0000..U+FFFF inline */
+                    ch <= 0xef &&
+                    (i+1) < srcLength &&
+                    (uint8_t)(src[i] - 0x80) <= 0x3f &&
+                    (uint8_t)(src[i+1] - 0x80) <= 0x3f
+                ) {
+                    reqLength++;
+                    i += 2;
+                    continue;
+                }
+            } else {
+                if( /* handle U+0000..U+07FF inline */
+                    ch >= 0xc0 &&
+                    i < srcLength &&
+                    (uint8_t)(src[i] - 0x80) <= 0x3f
+                ) {
+                    reqLength++;
+                    ++i;
+                    continue;
+                }
+            }
+
+            if(subchar < 0) {
+                *pErrorCode = U_INVALID_CHAR_FOUND;
+                return nullptr;
+            } else {
+                /* function call for error cases */
+                utf8_nextCharSafeBody((const uint8_t *)src, &(i), srcLength, ch, -1);
+                ++numSubstitutions;
+                reqLength+=U16_LENGTH(ch);
+            }
+        }
+    }
+
+    if(pNumSubstitutions!=nullptr) {
+        *pNumSubstitutions=numSubstitutions;
+    }
+
+    reqLength+=(int32_t)(pDest - dest);
+    if(pDestLength) {
+        *pDestLength = reqLength;
+    }
+
+    /* Terminate the buffer */
+    u_terminateUChars(dest, destCapacity, reqLength, pErrorCode);
+    return dest;
+}
+
+U_CAPI char* U_EXPORT2 
+u_strToJavaModifiedUTF8(
+        char *dest,
+        int32_t destCapacity,
+        int32_t *pDestLength,
+        const char16_t *src,
+        int32_t srcLength,
+        UErrorCode *pErrorCode) {
+    int32_t reqLength=0;
+    uint32_t ch=0;
+    const char16_t *pSrcLimit;
+    int32_t count;
+
+    /* args check */
+    if(U_FAILURE(*pErrorCode)){
+        return nullptr;
+    }
+    if( (src==nullptr && srcLength!=0) || srcLength < -1 ||
+        (dest==nullptr && destCapacity!=0) || destCapacity<0
+    ) {
+        *pErrorCode = U_ILLEGAL_ARGUMENT_ERROR;
+        return nullptr;
+    }
+    uint8_t *pDest = (uint8_t *)dest;
+    uint8_t *pDestLimit = pDest + destCapacity;
+
+    if(srcLength==-1) {
+        /* Convert NUL-terminated ASCII, then find the string length. */
+        while((ch=*src)<=0x7f && ch != 0 && pDest<pDestLimit) {
+            *pDest++ = (uint8_t)ch;
+            ++src;
+        }
+        if(ch == 0) {
+            reqLength=(int32_t)(pDest - (uint8_t *)dest);
+            if(pDestLength) {
+                *pDestLength = reqLength;
+            }
+
+            /* Terminate the buffer */
+            u_terminateChars(dest, destCapacity, reqLength, pErrorCode);
+            return dest;
+        }
+        srcLength = u_strlen(src);
+    }
+
+    /* Faster loop without ongoing checking for pSrcLimit and pDestLimit. */
+    pSrcLimit = (src!=nullptr)?(src+srcLength):nullptr;
+    for(;;) {
+        count = (int32_t)(pDestLimit - pDest);
+        srcLength = (int32_t)(pSrcLimit - src);
+        if(count >= srcLength && srcLength > 0 && *src <= 0x7f) {
+            /* fast ASCII loop */
+            const char16_t *prevSrc = src;
+            int32_t delta;
+            while(src < pSrcLimit && (ch = *src) <= 0x7f && ch != 0) {
+                *pDest++=(uint8_t)ch;
+                ++src;
+            }
+            delta = (int32_t)(src - prevSrc);
+            count -= delta;
+            srcLength -= delta;
+        }
+        /*
+         * Each iteration of the inner loop progresses by at most 3 UTF-8
+         * bytes and one char16_t.
+         */
+        count /= 3;
+        if(count > srcLength) {
+            count = srcLength; /* min(remaining dest/3, remaining src) */
+        }
+        if(count < 3) {
+            /*
+             * Too much overhead if we get near the end of the string,
+             * continue with the next loop.
+             */
+            break;
+        }
+        do {
+            ch=*src++;
+            if(ch <= 0x7f && ch != 0) {
+                *pDest++ = (uint8_t)ch;
+            } else if(ch <= 0x7ff) {
+                *pDest++=(uint8_t)((ch>>6)|0xc0);
+                *pDest++=(uint8_t)((ch&0x3f)|0x80);
+            } else {
+                *pDest++=(uint8_t)((ch>>12)|0xe0);
+                *pDest++=(uint8_t)(((ch>>6)&0x3f)|0x80);
+                *pDest++=(uint8_t)((ch&0x3f)|0x80);
+            }
+        } while(--count > 0);
+    }
+
+    while(src<pSrcLimit) {
+        ch=*src++;
+        if(ch <= 0x7f && ch != 0) {
+            if(pDest<pDestLimit) {
+                *pDest++ = (uint8_t)ch;
+            } else {
+                reqLength = 1;
+                break;
+            }
+        } else if(ch <= 0x7ff) {
+            if((pDestLimit - pDest) >= 2) {
+                *pDest++=(uint8_t)((ch>>6)|0xc0);
+                *pDest++=(uint8_t)((ch&0x3f)|0x80);
+            } else {
+                reqLength = 2;
+                break;
+            }
+        } else {
+            if((pDestLimit - pDest) >= 3) {
+                *pDest++=(uint8_t)((ch>>12)|0xe0);
+                *pDest++=(uint8_t)(((ch>>6)&0x3f)|0x80);
+                *pDest++=(uint8_t)((ch&0x3f)|0x80);
+            } else {
+                reqLength = 3;
+                break;
+            }
+        }
+    }
+    while(src<pSrcLimit) {
+        ch=*src++;
+        if(ch <= 0x7f && ch != 0) {
+            ++reqLength;
+        } else if(ch<=0x7ff) {
+            reqLength+=2;
+        } else {
+            reqLength+=3;
+        }
+    }
+
+    reqLength+=(int32_t)(pDest - (uint8_t *)dest);
+    if(pDestLength){
+        *pDestLength = reqLength;
+    }
+
+    /* Terminate the buffer */
+    u_terminateChars(dest, destCapacity, reqLength, pErrorCode);
+    return dest;
+}