Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

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

1 files changed, 565 insertions, 0 deletions

diff --git a/mozglue/misc/SIMD.cpp b/mozglue/misc/SIMD.cpp
new file mode 100644
index 0000000000..3893de57b3
--- /dev/null
+++ b/mozglue/misc/SIMD.cpp
@@ -0,0 +1,565 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/SIMD.h"
+
+#include <cstring>
+#include <stdint.h>
+#include <type_traits>
+
+#include "mozilla/EndianUtils.h"
+#include "mozilla/SSE.h"
+
+#ifdef MOZILLA_PRESUME_SSE2
+
+#  include <immintrin.h>
+
+#endif
+
+namespace mozilla {
+
+template <typename TValue>
+const TValue* FindInBufferNaive(const TValue* ptr, TValue value,
+                                size_t length) {
+  const TValue* end = ptr + length;
+  while (ptr < end) {
+    if (*ptr == value) {
+      return ptr;
+    }
+    ptr++;
+  }
+  return nullptr;
+}
+
+#ifdef MOZILLA_PRESUME_SSE2
+
+const __m128i* Cast128(uintptr_t ptr) {
+  return reinterpret_cast<const __m128i*>(ptr);
+}
+
+template <typename T>
+T GetAs(uintptr_t ptr) {
+  return *reinterpret_cast<const T*>(ptr);
+}
+
+// Akin to ceil/floor, AlignDown/AlignUp will return the original pointer if it
+// is already aligned.
+uintptr_t AlignDown16(uintptr_t ptr) { return ptr & ~0xf; }
+
+uintptr_t AlignUp16(uintptr_t ptr) { return AlignDown16(ptr + 0xf); }
+
+template <typename TValue>
+__m128i CmpEq128(__m128i a, __m128i b) {
+  static_assert(sizeof(TValue) == 1 || sizeof(TValue) == 2);
+  if (sizeof(TValue) == 1) {
+    return _mm_cmpeq_epi8(a, b);
+  }
+  return _mm_cmpeq_epi16(a, b);
+}
+
+#  ifdef __GNUC__
+
+// Earlier versions of GCC are missing the _mm_loadu_si32 instruction. This
+// workaround from Peter Cordes (https://stackoverflow.com/a/72837992) compiles
+// down to the same instructions. We could just replace _mm_loadu_si32
+__m128i Load32BitsIntoXMM(uintptr_t ptr) {
+  int tmp;
+  memcpy(&tmp, reinterpret_cast<const void*>(ptr),
+         sizeof(tmp));            // unaligned aliasing-safe load
+  return _mm_cvtsi32_si128(tmp);  // efficient on GCC/clang/MSVC
+}
+
+#  else
+
+__m128i Load32BitsIntoXMM(uintptr_t ptr) {
+  return _mm_loadu_si32(Cast128(ptr));
+}
+
+#  endif
+
+const char* Check4x4Chars(__m128i needle, uintptr_t a, uintptr_t b, uintptr_t c,
+                          uintptr_t d) {
+  __m128i haystackA = Load32BitsIntoXMM(a);
+  __m128i cmpA = CmpEq128<char>(needle, haystackA);
+  __m128i haystackB = Load32BitsIntoXMM(b);
+  __m128i cmpB = CmpEq128<char>(needle, haystackB);
+  __m128i haystackC = Load32BitsIntoXMM(c);
+  __m128i cmpC = CmpEq128<char>(needle, haystackC);
+  __m128i haystackD = Load32BitsIntoXMM(d);
+  __m128i cmpD = CmpEq128<char>(needle, haystackD);
+  __m128i or_ab = _mm_or_si128(cmpA, cmpB);
+  __m128i or_cd = _mm_or_si128(cmpC, cmpD);
+  __m128i or_abcd = _mm_or_si128(or_ab, or_cd);
+  int orMask = _mm_movemask_epi8(or_abcd);
+  if (orMask & 0xf) {
+    int cmpMask;
+    cmpMask = _mm_movemask_epi8(cmpA);
+    if (cmpMask & 0xf) {
+      return reinterpret_cast<const char*>(a + __builtin_ctz(cmpMask));
+    }
+    cmpMask = _mm_movemask_epi8(cmpB);
+    if (cmpMask & 0xf) {
+      return reinterpret_cast<const char*>(b + __builtin_ctz(cmpMask));
+    }
+    cmpMask = _mm_movemask_epi8(cmpC);
+    if (cmpMask & 0xf) {
+      return reinterpret_cast<const char*>(c + __builtin_ctz(cmpMask));
+    }
+    cmpMask = _mm_movemask_epi8(cmpD);
+    if (cmpMask & 0xf) {
+      return reinterpret_cast<const char*>(d + __builtin_ctz(cmpMask));
+    }
+  }
+
+  return nullptr;
+}
+
+template <typename TValue>
+const TValue* Check4x16Bytes(__m128i needle, uintptr_t a, uintptr_t b,
+                             uintptr_t c, uintptr_t d) {
+  __m128i haystackA = _mm_loadu_si128(Cast128(a));
+  __m128i cmpA = CmpEq128<TValue>(needle, haystackA);
+  __m128i haystackB = _mm_loadu_si128(Cast128(b));
+  __m128i cmpB = CmpEq128<TValue>(needle, haystackB);
+  __m128i haystackC = _mm_loadu_si128(Cast128(c));
+  __m128i cmpC = CmpEq128<TValue>(needle, haystackC);
+  __m128i haystackD = _mm_loadu_si128(Cast128(d));
+  __m128i cmpD = CmpEq128<TValue>(needle, haystackD);
+  __m128i or_ab = _mm_or_si128(cmpA, cmpB);
+  __m128i or_cd = _mm_or_si128(cmpC, cmpD);
+  __m128i or_abcd = _mm_or_si128(or_ab, or_cd);
+  int orMask = _mm_movemask_epi8(or_abcd);
+  if (orMask) {
+    int cmpMask;
+    cmpMask = _mm_movemask_epi8(cmpA);
+    if (cmpMask) {
+      return reinterpret_cast<const TValue*>(a + __builtin_ctz(cmpMask));
+    }
+    cmpMask = _mm_movemask_epi8(cmpB);
+    if (cmpMask) {
+      return reinterpret_cast<const TValue*>(b + __builtin_ctz(cmpMask));
+    }
+    cmpMask = _mm_movemask_epi8(cmpC);
+    if (cmpMask) {
+      return reinterpret_cast<const TValue*>(c + __builtin_ctz(cmpMask));
+    }
+    cmpMask = _mm_movemask_epi8(cmpD);
+    if (cmpMask) {
+      return reinterpret_cast<const TValue*>(d + __builtin_ctz(cmpMask));
+    }
+  }
+
+  return nullptr;
+}
+
+enum class HaystackOverlap {
+  Overlapping,
+  Sequential,
+};
+
+// Check two 16-byte chunks for the two-byte sequence loaded into needle1
+// followed by needle1. `carryOut` is an optional pointer which we will
+// populate based on whether the last character of b matches needle1. This
+// should be provided on subsequent calls via `carryIn` so we can detect cases
+// where the last byte of b's 16-byte chunk is needle1 and the first byte of
+// the next a's 16-byte chunk is needle2. `overlap` and whether
+// `carryIn`/`carryOut` are NULL should be knowable at compile time to avoid
+// branching.
+template <typename TValue>
+const TValue* Check2x2x16Bytes(__m128i needle1, __m128i needle2, uintptr_t a,
+                               uintptr_t b, __m128i* carryIn, __m128i* carryOut,
+                               HaystackOverlap overlap) {
+  const int shiftRightAmount = 16 - sizeof(TValue);
+  const int shiftLeftAmount = sizeof(TValue);
+  __m128i haystackA = _mm_loadu_si128(Cast128(a));
+  __m128i cmpA1 = CmpEq128<TValue>(needle1, haystackA);
+  __m128i cmpA2 = CmpEq128<TValue>(needle2, haystackA);
+  __m128i cmpA;
+  if (carryIn) {
+    cmpA = _mm_and_si128(
+        _mm_or_si128(_mm_bslli_si128(cmpA1, shiftLeftAmount), *carryIn), cmpA2);
+  } else {
+    cmpA = _mm_and_si128(_mm_bslli_si128(cmpA1, shiftLeftAmount), cmpA2);
+  }
+  __m128i haystackB = _mm_loadu_si128(Cast128(b));
+  __m128i cmpB1 = CmpEq128<TValue>(needle1, haystackB);
+  __m128i cmpB2 = CmpEq128<TValue>(needle2, haystackB);
+  __m128i cmpB;
+  if (overlap == HaystackOverlap::Overlapping) {
+    cmpB = _mm_and_si128(_mm_bslli_si128(cmpB1, shiftLeftAmount), cmpB2);
+  } else {
+    MOZ_ASSERT(overlap == HaystackOverlap::Sequential);
+    __m128i carryAB = _mm_bsrli_si128(cmpA1, shiftRightAmount);
+    cmpB = _mm_and_si128(
+        _mm_or_si128(_mm_bslli_si128(cmpB1, shiftLeftAmount), carryAB), cmpB2);
+  }
+  __m128i or_ab = _mm_or_si128(cmpA, cmpB);
+  int orMask = _mm_movemask_epi8(or_ab);
+  if (orMask) {
+    int cmpMask;
+    cmpMask = _mm_movemask_epi8(cmpA);
+    if (cmpMask) {
+      return reinterpret_cast<const TValue*>(a + __builtin_ctz(cmpMask) -
+                                             shiftLeftAmount);
+    }
+    cmpMask = _mm_movemask_epi8(cmpB);
+    if (cmpMask) {
+      return reinterpret_cast<const TValue*>(b + __builtin_ctz(cmpMask) -
+                                             shiftLeftAmount);
+    }
+  }
+
+  if (carryOut) {
+    _mm_store_si128(carryOut, _mm_bsrli_si128(cmpB1, shiftRightAmount));
+  }
+
+  return nullptr;
+}
+
+template <typename TValue>
+const TValue* FindInBuffer(const TValue* ptr, TValue value, size_t length) {
+  static_assert(sizeof(TValue) == 1 || sizeof(TValue) == 2);
+  static_assert(std::is_unsigned<TValue>::value);
+  uint64_t splat64;
+  if (sizeof(TValue) == 1) {
+    splat64 = 0x0101010101010101llu;
+  } else {
+    splat64 = 0x0001000100010001llu;
+  }
+
+  // Load our needle into a 16-byte register
+  uint64_t u64_value = static_cast<uint64_t>(value) * splat64;
+  int64_t i64_value = *reinterpret_cast<int64_t*>(&u64_value);
+  __m128i needle = _mm_set_epi64x(i64_value, i64_value);
+
+  size_t numBytes = length * sizeof(TValue);
+  uintptr_t cur = reinterpret_cast<uintptr_t>(ptr);
+  uintptr_t end = cur + numBytes;
+
+  if ((sizeof(TValue) > 1 && numBytes < 16) || numBytes < 4) {
+    while (cur < end) {
+      if (GetAs<TValue>(cur) == value) {
+        return reinterpret_cast<const TValue*>(cur);
+      }
+      cur += sizeof(TValue);
+    }
+    return nullptr;
+  }
+
+  if (numBytes < 16) {
+    // NOTE: here and below, we have some bit fiddling which could look a
+    // little weird. The important thing to note though is it's just a trick
+    // for getting the number 4 if numBytes is greater than or equal to 8,
+    // and 0 otherwise. This lets us fully cover the range without any
+    // branching for the case where numBytes is in [4,8), and [8,16). We get
+    // four ranges from this - if numbytes > 8, we get:
+    //   [0,4), [4,8], [end - 8), [end - 4)
+    // and if numbytes < 8, we get
+    //   [0,4), [0,4), [end - 4), [end - 4)
+    uintptr_t a = cur;
+    uintptr_t b = cur + ((numBytes & 8) >> 1);
+    uintptr_t c = end - 4 - ((numBytes & 8) >> 1);
+    uintptr_t d = end - 4;
+    const char* charResult = Check4x4Chars(needle, a, b, c, d);
+    // Note: we ensure above that sizeof(TValue) == 1 here, so this is
+    // either char to char or char to something like a uint8_t.
+    return reinterpret_cast<const TValue*>(charResult);
+  }
+
+  if (numBytes < 64) {
+    // NOTE: see the above explanation of the similar chunk of code, but in
+    // this case, replace 8 with 32 and 4 with 16.
+    uintptr_t a = cur;
+    uintptr_t b = cur + ((numBytes & 32) >> 1);
+    uintptr_t c = end - 16 - ((numBytes & 32) >> 1);
+    uintptr_t d = end - 16;
+    return Check4x16Bytes<TValue>(needle, a, b, c, d);
+  }
+
+  // Get the initial unaligned load out of the way. This will overlap with the
+  // aligned stuff below, but the overlapped part should effectively be free
+  // (relative to a mispredict from doing a byte-by-byte loop).
+  __m128i haystack = _mm_loadu_si128(Cast128(cur));
+  __m128i cmp = CmpEq128<TValue>(needle, haystack);
+  int cmpMask = _mm_movemask_epi8(cmp);
+  if (cmpMask) {
+    return reinterpret_cast<const TValue*>(cur + __builtin_ctz(cmpMask));
+  }
+
+  // Now we're working with aligned memory. Hooray! \o/
+  cur = AlignUp16(cur);
+
+  // The address of the final 48-63 bytes. We overlap this with what we check in
+  // our hot loop below to avoid branching. Again, the overlap should be
+  // negligible compared with a branch mispredict.
+  uintptr_t tailStartPtr = AlignDown16(end - 48);
+  uintptr_t tailEndPtr = end - 16;
+
+  while (cur < tailStartPtr) {
+    uintptr_t a = cur;
+    uintptr_t b = cur + 16;
+    uintptr_t c = cur + 32;
+    uintptr_t d = cur + 48;
+    const TValue* result = Check4x16Bytes<TValue>(needle, a, b, c, d);
+    if (result) {
+      return result;
+    }
+    cur += 64;
+  }
+
+  uintptr_t a = tailStartPtr;
+  uintptr_t b = tailStartPtr + 16;
+  uintptr_t c = tailStartPtr + 32;
+  uintptr_t d = tailEndPtr;
+  return Check4x16Bytes<TValue>(needle, a, b, c, d);
+}
+
+template <typename TValue>
+const TValue* TwoElementLoop(uintptr_t start, uintptr_t end, TValue v1,
+                             TValue v2) {
+  static_assert(sizeof(TValue) == 1 || sizeof(TValue) == 2);
+
+  const TValue* cur = reinterpret_cast<const TValue*>(start);
+  const TValue* preEnd = reinterpret_cast<const TValue*>(end - sizeof(TValue));
+
+  uint32_t expected = static_cast<uint32_t>(v1) |
+                      (static_cast<uint32_t>(v2) << (sizeof(TValue) * 8));
+  while (cur < preEnd) {
+    // NOTE: this should only ever be called on little endian architectures.
+    static_assert(MOZ_LITTLE_ENDIAN());
+    // We or cur[0] and cur[1] together explicitly and compare to expected,
+    // in order to avoid UB from just loading them as a uint16_t/uint32_t.
+    // However, it will compile down the same code after optimizations on
+    // little endian systems which support unaligned loads. Comparing them
+    // value-by-value, however, will not, and seems to perform worse in local
+    // microbenchmarking. Even after bitwise or'ing the comparison values
+    // together to avoid the short circuit, the compiler doesn't seem to get
+    // the hint and creates two branches, the first of which might be
+    // frequently mispredicted.
+    uint32_t actual = static_cast<uint32_t>(cur[0]) |
+                      (static_cast<uint32_t>(cur[1]) << (sizeof(TValue) * 8));
+    if (actual == expected) {
+      return cur;
+    }
+    cur++;
+  }
+  return nullptr;
+}
+
+template <typename TValue>
+const TValue* FindTwoInBuffer(const TValue* ptr, TValue v1, TValue v2,
+                              size_t length) {
+  static_assert(sizeof(TValue) == 1 || sizeof(TValue) == 2);
+  static_assert(std::is_unsigned<TValue>::value);
+  uint64_t splat64;
+  if (sizeof(TValue) == 1) {
+    splat64 = 0x0101010101010101llu;
+  } else {
+    splat64 = 0x0001000100010001llu;
+  }
+
+  // Load our needle into a 16-byte register
+  uint64_t u64_v1 = static_cast<uint64_t>(v1) * splat64;
+  int64_t i64_v1 = *reinterpret_cast<int64_t*>(&u64_v1);
+  __m128i needle1 = _mm_set_epi64x(i64_v1, i64_v1);
+  uint64_t u64_v2 = static_cast<uint64_t>(v2) * splat64;
+  int64_t i64_v2 = *reinterpret_cast<int64_t*>(&u64_v2);
+  __m128i needle2 = _mm_set_epi64x(i64_v2, i64_v2);
+
+  size_t numBytes = length * sizeof(TValue);
+  uintptr_t cur = reinterpret_cast<uintptr_t>(ptr);
+  uintptr_t end = cur + numBytes;
+
+  if (numBytes < 16) {
+    return TwoElementLoop<TValue>(cur, end, v1, v2);
+  }
+
+  if (numBytes < 32) {
+    uintptr_t a = cur;
+    uintptr_t b = end - 16;
+    return Check2x2x16Bytes<TValue>(needle1, needle2, a, b, nullptr, nullptr,
+                                    HaystackOverlap::Overlapping);
+  }
+
+  // Get the initial unaligned load out of the way. This will likely overlap
+  // with the aligned stuff below, but the overlapped part should effectively
+  // be free.
+  __m128i haystack = _mm_loadu_si128(Cast128(cur));
+  __m128i cmp1 = CmpEq128<TValue>(needle1, haystack);
+  __m128i cmp2 = CmpEq128<TValue>(needle2, haystack);
+  int cmpMask1 = _mm_movemask_epi8(cmp1);
+  int cmpMask2 = _mm_movemask_epi8(cmp2);
+  int cmpMask = (cmpMask1 << sizeof(TValue)) & cmpMask2;
+  if (cmpMask) {
+    return reinterpret_cast<const TValue*>(cur + __builtin_ctz(cmpMask) -
+                                           sizeof(TValue));
+  }
+
+  // Now we're working with aligned memory. Hooray! \o/
+  cur = AlignUp16(cur);
+
+  // The address of the final 48-63 bytes. We overlap this with what we check in
+  // our hot loop below to avoid branching. Again, the overlap should be
+  // negligible compared with a branch mispredict.
+  uintptr_t tailEndPtr = end - 16;
+  uintptr_t tailStartPtr = AlignDown16(tailEndPtr);
+
+  __m128i cmpMaskCarry = _mm_set1_epi32(0);
+  while (cur < tailStartPtr) {
+    uintptr_t a = cur;
+    uintptr_t b = cur + 16;
+    const TValue* result =
+        Check2x2x16Bytes<TValue>(needle1, needle2, a, b, &cmpMaskCarry,
+                                 &cmpMaskCarry, HaystackOverlap::Sequential);
+    if (result) {
+      return result;
+    }
+    cur += 32;
+  }
+
+  uint32_t carry = (cur == tailStartPtr) ? 0xffffffff : 0;
+  __m128i wideCarry = Load32BitsIntoXMM(reinterpret_cast<uintptr_t>(&carry));
+  cmpMaskCarry = _mm_and_si128(cmpMaskCarry, wideCarry);
+  uintptr_t a = tailStartPtr;
+  uintptr_t b = tailEndPtr;
+  return Check2x2x16Bytes<TValue>(needle1, needle2, a, b, &cmpMaskCarry,
+                                  nullptr, HaystackOverlap::Overlapping);
+}
+
+const char* SIMD::memchr8SSE2(const char* ptr, char value, size_t length) {
+  // Signed chars are just really annoying to do bit logic with. Convert to
+  // unsigned at the outermost scope so we don't have to worry about it.
+  const unsigned char* uptr = reinterpret_cast<const unsigned char*>(ptr);
+  unsigned char uvalue = static_cast<unsigned char>(value);
+  const unsigned char* uresult =
+      FindInBuffer<unsigned char>(uptr, uvalue, length);
+  return reinterpret_cast<const char*>(uresult);
+}
+
+// So, this is a bit awkward. It generally simplifies things if we can just
+// assume all the AVX2 code is 64-bit, so we have this preprocessor guard
+// in SIMD_avx2 over all of its actual code, and it also defines versions
+// of its endpoints that just assert false if the guard is not satisfied.
+// A 32 bit processor could implement the AVX2 instruction set though, which
+// would result in it passing the supports_avx2() check and landing in an
+// assertion failure. Accordingly, we just don't allow that to happen. We
+// are not particularly concerned about ensuring that newer 32 bit processors
+// get access to the AVX2 functions exposed here.
+#  if defined(MOZILLA_MAY_SUPPORT_AVX2) && defined(__x86_64__)
+
+bool SupportsAVX2() { return supports_avx2(); }
+
+#  else
+
+bool SupportsAVX2() { return false; }
+
+#  endif
+
+const char* SIMD::memchr8(const char* ptr, char value, size_t length) {
+  if (SupportsAVX2()) {
+    return memchr8AVX2(ptr, value, length);
+  }
+  return memchr8SSE2(ptr, value, length);
+}
+
+const char16_t* SIMD::memchr16SSE2(const char16_t* ptr, char16_t value,
+                                   size_t length) {
+  return FindInBuffer<char16_t>(ptr, value, length);
+}
+
+const char16_t* SIMD::memchr16(const char16_t* ptr, char16_t value,
+                               size_t length) {
+  if (SupportsAVX2()) {
+    return memchr16AVX2(ptr, value, length);
+  }
+  return memchr16SSE2(ptr, value, length);
+}
+
+const uint64_t* SIMD::memchr64(const uint64_t* ptr, uint64_t value,
+                               size_t length) {
+  if (SupportsAVX2()) {
+    return memchr64AVX2(ptr, value, length);
+  }
+  return FindInBufferNaive<uint64_t>(ptr, value, length);
+}
+
+const char* SIMD::memchr2x8(const char* ptr, char v1, char v2, size_t length) {
+  // Signed chars are just really annoying to do bit logic with. Convert to
+  // unsigned at the outermost scope so we don't have to worry about it.
+  const unsigned char* uptr = reinterpret_cast<const unsigned char*>(ptr);
+  unsigned char uv1 = static_cast<unsigned char>(v1);
+  unsigned char uv2 = static_cast<unsigned char>(v2);
+  const unsigned char* uresult =
+      FindTwoInBuffer<unsigned char>(uptr, uv1, uv2, length);
+  return reinterpret_cast<const char*>(uresult);
+}
+
+const char16_t* SIMD::memchr2x16(const char16_t* ptr, char16_t v1, char16_t v2,
+                                 size_t length) {
+  return FindTwoInBuffer<char16_t>(ptr, v1, v2, length);
+}
+
+#else
+
+const char* SIMD::memchr8(const char* ptr, char value, size_t length) {
+  const void* result = ::memchr(reinterpret_cast<const void*>(ptr),
+                                static_cast<int>(value), length);
+  return reinterpret_cast<const char*>(result);
+}
+
+const char* SIMD::memchr8SSE2(const char* ptr, char value, size_t length) {
+  return memchr8(ptr, value, length);
+}
+
+const char16_t* SIMD::memchr16(const char16_t* ptr, char16_t value,
+                               size_t length) {
+  return FindInBufferNaive<char16_t>(ptr, value, length);
+}
+
+const char16_t* SIMD::memchr16SSE2(const char16_t* ptr, char16_t value,
+                                   size_t length) {
+  return memchr16(ptr, value, length);
+}
+
+const uint64_t* SIMD::memchr64(const uint64_t* ptr, uint64_t value,
+                               size_t length) {
+  return FindInBufferNaive<uint64_t>(ptr, value, length);
+}
+
+const char* SIMD::memchr2x8(const char* ptr, char v1, char v2, size_t length) {
+  const char* end = ptr + length - 1;
+  while (ptr < end) {
+    ptr = memchr8(ptr, v1, end - ptr);
+    if (!ptr) {
+      return nullptr;
+    }
+    if (ptr[1] == v2) {
+      return ptr;
+    }
+    ptr++;
+  }
+  return nullptr;
+}
+
+const char16_t* SIMD::memchr2x16(const char16_t* ptr, char16_t v1, char16_t v2,
+                                 size_t length) {
+  const char16_t* end = ptr + length - 1;
+  while (ptr < end) {
+    ptr = memchr16(ptr, v1, end - ptr);
+    if (!ptr) {
+      return nullptr;
+    }
+    if (ptr[1] == v2) {
+      return ptr;
+    }
+    ptr++;
+  }
+  return nullptr;
+}
+
+#endif
+
+}  // namespace mozilla