path: root/js/src/util/DoubleToString.cpp

/* -*- 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/. */

/*
 * Portable double to alphanumeric string and back converters.
 */

#include "util/DoubleToString.h"

#include "mozilla/EndianUtils.h"

#include "js/Utility.h"

using namespace js;

#if MOZ_LITTLE_ENDIAN()
#  define IEEE_8087
#else
#  define IEEE_MC68k
#endif

#ifndef Long
#  define Long int32_t
#endif

#ifndef ULong
#  define ULong uint32_t
#endif

/*
#ifndef Llong
#define Llong int64_t
#endif

#ifndef ULlong
#define ULlong uint64_t
#endif
*/

// dtoa.c requires that MALLOC be infallible. Furthermore, its allocations are
// few and small. So AutoEnterOOMUnsafeRegion is appropriate here.
static inline void* dtoa_malloc(size_t size) {
  AutoEnterOOMUnsafeRegion oomUnsafe;
  void* p = js_malloc(size);
  if (!p) oomUnsafe.crash("dtoa_malloc");

  return p;
}

static inline void dtoa_free(void* p) { return js_free(p); }

#define NO_GLOBAL_STATE
#define NO_ERRNO
#define Omit_Private_Memory  // This saves memory for the workloads we see.
#define MALLOC dtoa_malloc
#define FREE dtoa_free
#include "dtoa.c"

/* Let b = floor(b / divisor), and return the remainder.  b must be nonnegative.
 * divisor must be between 1 and 65536.
 * This function cannot run out of memory. */
static uint32_t divrem(Bigint* b, uint32_t divisor) {
  int32_t n = b->wds;
  uint32_t remainder = 0;
  ULong* bx;
  ULong* bp;

  MOZ_ASSERT(divisor > 0 && divisor <= 65536);

  if (!n) return 0; /* b is zero */
  bx = b->x;
  bp = bx + n;
  do {
    ULong a = *--bp;
    ULong dividend = remainder << 16 | a >> 16;
    ULong quotientHi = dividend / divisor;
    ULong quotientLo;

    remainder = dividend - quotientHi * divisor;
    MOZ_ASSERT(quotientHi <= 0xFFFF && remainder < divisor);
    dividend = remainder << 16 | (a & 0xFFFF);
    quotientLo = dividend / divisor;
    remainder = dividend - quotientLo * divisor;
    MOZ_ASSERT(quotientLo <= 0xFFFF && remainder < divisor);
    *bp = quotientHi << 16 | quotientLo;
  } while (bp != bx);
  /* Decrease the size of the number if its most significant word is now zero.
   */
  if (bx[n - 1] == 0) b->wds--;
  return remainder;
}

/* Return floor(b/2^k) and set b to be the remainder.  The returned quotient
 * must be less than 2^32. */
static uint32_t quorem2(Bigint* b, int32_t k) {
  ULong mask;
  ULong result;
  ULong* bx;
  ULong* bxe;
  int32_t w;
  int32_t n = k >> 5;
  k &= 0x1F;
  mask = (ULong(1) << k) - 1;

  w = b->wds - n;
  if (w <= 0) return 0;
  MOZ_ASSERT(w <= 2);
  bx = b->x;
  bxe = bx + n;
  result = *bxe >> k;
  *bxe &= mask;
  if (w == 2) {
    MOZ_ASSERT(!(bxe[1] & ~mask));
    if (k) result |= bxe[1] << (32 - k);
  }
  n++;
  while (!*bxe && bxe != bx) {
    n--;
    bxe--;
  }
  b->wds = n;
  return result;
}

/* "-0.0000...(1073 zeros after decimal point)...0001\0" is the longest string
 * that we could produce, which occurs when printing -5e-324 in binary.  We
 * could compute a better estimate of the size of the output string and malloc
 * fewer bytes depending on d and base, but why bother? */
#define DTOBASESTR_BUFFER_SIZE 1078
#define BASEDIGIT(digit) \
  ((char)(((digit) >= 10) ? 'a' - 10 + (digit) : '0' + (digit)))

char* js_dtobasestr(DtoaState* state, int base, double dinput) {
  U d;
  char* buffer; /* The output string */
  char* p;      /* Pointer to current position in the buffer */
  char* pInt;   /* Pointer to the beginning of the integer part of the string */
  char* q;
  uint32_t digit;
  U di; /* d truncated to an integer */
  U df; /* The fractional part of d */

  MOZ_ASSERT(base >= 2 && base <= 36);

  dval(d) = dinput;
  buffer = js_pod_malloc<char>(DTOBASESTR_BUFFER_SIZE);
  if (!buffer) return nullptr;
  p = buffer;

  if (dval(d) < 0.0) {
    *p++ = '-';
    dval(d) = -dval(d);
  }

  /* Check for Infinity and NaN */
  if ((word0(d) & Exp_mask) == Exp_mask) {
    strcpy(p, !word1(d) && !(word0(d) & Frac_mask) ? "Infinity" : "NaN");
    return buffer;
  }

  /* Output the integer part of d with the digits in reverse order. */
  pInt = p;
  dval(di) = floor(dval(d));
  if (dval(di) <= 4294967295.0) {
    uint32_t n = (uint32_t)dval(di);
    if (n) do {
        uint32_t m = n / base;
        digit = n - m * base;
        n = m;
        MOZ_ASSERT(digit < (uint32_t)base);
        *p++ = BASEDIGIT(digit);
      } while (n);
    else
      *p++ = '0';
  } else {
    int e;
    int bits; /* Number of significant bits in di; not used. */
    Bigint* b = d2b(PASS_STATE di, &e, &bits);
    if (!b) goto nomem1;
    b = lshift(PASS_STATE b, e);
    if (!b) {
    nomem1:
      Bfree(PASS_STATE b);
      js_free(buffer);
      return nullptr;
    }
    do {
      digit = divrem(b, base);
      MOZ_ASSERT(digit < (uint32_t)base);
      *p++ = BASEDIGIT(digit);
    } while (b->wds);
    Bfree(PASS_STATE b);
  }
  /* Reverse the digits of the integer part of d. */
  q = p - 1;
  while (q > pInt) {
    char ch = *pInt;
    *pInt++ = *q;
    *q-- = ch;
  }

  dval(df) = dval(d) - dval(di);
  if (dval(df) != 0.0) {
    /* We have a fraction. */
    int e, bbits;
    int32_t s2, done;
    Bigint* b = nullptr;
    Bigint* s = nullptr;
    Bigint* mlo = nullptr;
    Bigint* mhi = nullptr;

    *p++ = '.';
    b = d2b(PASS_STATE df, &e, &bbits);
    if (!b) {
    nomem2:
      Bfree(PASS_STATE b);
      Bfree(PASS_STATE s);
      if (mlo != mhi) Bfree(PASS_STATE mlo);
      Bfree(PASS_STATE mhi);
      js_free(buffer);
      return nullptr;
    }
    MOZ_ASSERT(e < 0);
    /* At this point df = b * 2^e.  e must be less than zero because 0 < df < 1.
     */

    s2 = -(int32_t)(word0(d) >> Exp_shift1 & Exp_mask >> Exp_shift1);
#ifndef Sudden_Underflow
    if (!s2) s2 = -1;
#endif
    s2 += Bias + P;
    /* 1/2^s2 = (nextDouble(d) - d)/2 */
    MOZ_ASSERT(-s2 < e);
    mlo = i2b(PASS_STATE 1);
    if (!mlo) goto nomem2;
    mhi = mlo;
    if (!word1(d) && !(word0(d) & Bndry_mask)
#ifndef Sudden_Underflow
        && word0(d) & (Exp_mask & Exp_mask << 1)
#endif
    ) {
      /* The special case.  Here we want to be within a quarter of the last
         input significant digit instead of one half of it when the output
         string's value is less than d.  */
      s2 += Log2P;
      mhi = i2b(PASS_STATE 1 << Log2P);
      if (!mhi) goto nomem2;
    }
    b = lshift(PASS_STATE b, e + s2);
    if (!b) goto nomem2;
    s = i2b(PASS_STATE 1);
    if (!s) goto nomem2;
    s = lshift(PASS_STATE s, s2);
    if (!s) goto nomem2;
    /* At this point we have the following:
     *   s = 2^s2;
     *   1 > df = b/2^s2 > 0;
     *   (d - prevDouble(d))/2 = mlo/2^s2;
     *   (nextDouble(d) - d)/2 = mhi/2^s2. */

    done = false;
    do {
      int32_t j, j1;
      Bigint* delta;

      b = multadd(PASS_STATE b, base, 0);
      if (!b) goto nomem2;
      digit = quorem2(b, s2);
      if (mlo == mhi) {
        mlo = mhi = multadd(PASS_STATE mlo, base, 0);
        if (!mhi) goto nomem2;
      } else {
        mlo = multadd(PASS_STATE mlo, base, 0);
        if (!mlo) goto nomem2;
        mhi = multadd(PASS_STATE mhi, base, 0);
        if (!mhi) goto nomem2;
      }

      /* Do we yet have the shortest string that will round to d? */
      j = cmp(b, mlo);
      /* j is b/2^s2 compared with mlo/2^s2. */
      delta = diff(PASS_STATE s, mhi);
      if (!delta) goto nomem2;
      j1 = delta->sign ? 1 : cmp(b, delta);
      Bfree(PASS_STATE delta);
      /* j1 is b/2^s2 compared with 1 - mhi/2^s2. */

#ifndef ROUND_BIASED
      if (j1 == 0 && !(word1(d) & 1)) {
        if (j > 0) digit++;
        done = true;
      } else
#endif
          if (j < 0 || (j == 0
#ifndef ROUND_BIASED
                        && !(word1(d) & 1)
#endif
                            )) {
        if (j1 > 0) {
          /* Either dig or dig+1 would work here as the least significant digit.
             Use whichever would produce an output value closer to d. */
          b = lshift(PASS_STATE b, 1);
          if (!b) goto nomem2;
          j1 = cmp(b, s);
          if (j1 > 0) /* The even test (|| (j1 == 0 && (digit & 1))) is not here
                       * because it messes up odd base output such as 3.5 in
                       * base 3.  */
            digit++;
        }
        done = true;
      } else if (j1 > 0) {
        digit++;
        done = true;
      }
      MOZ_ASSERT(digit < (uint32_t)base);
      *p++ = BASEDIGIT(digit);
    } while (!done);
    Bfree(PASS_STATE b);
    Bfree(PASS_STATE s);
    if (mlo != mhi) Bfree(PASS_STATE mlo);
    Bfree(PASS_STATE mhi);
  }
  MOZ_ASSERT(p < buffer + DTOBASESTR_BUFFER_SIZE);
  *p = '\0';
  return buffer;
}

DtoaState* js::NewDtoaState() { return newdtoa(); }

void js::DestroyDtoaState(DtoaState* state) { destroydtoa(state); }

/* Cleanup pollution from dtoa.c */
#undef Bias