strtold.c

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/* Copyright (C) 1994 DJ Delorie, see COPYING.DJ for details */
#include <stdlib.h>
#include <msvcrt/ctype.h>

static double powten[] =
{
  1e1L, 1e2L, 1e4L, 1e8L, 1e16L, 1e32L, 1e64L, 1e128L, 1e256L,
#ifdef __GNUC__
  1e512L, 1e512L*1e512L, 1e2048L, 1e4096L
#else
  1e256L, 1e256L, 1e256L, 1e256L
#endif
};

long double
_strtold(const char *s, char **sret)
{
  double r;     /* result */
  int e, ne;            /* exponent */
  int sign;         /* +- 1.0 */
  int esign;
  int flags=0;
  int l2powm1;

  r = 0.0L;
  sign = 1;
  e = ne = 0;
  esign = 1;

  while(*s && isspace(*s))
    s++;

  if (*s == '+')
    s++;
  else if (*s == '-')
  {
    sign = -1;
    s++;
  }

  while ((*s >= '0') && (*s <= '9'))
  {
    flags |= 1;
    r *= 10.0L;
    r += *s - '0';
    s++;
  }

  if (*s == '.')
  {
    s++;
    while ((*s >= '0') && (*s <= '9'))
    {
      flags |= 2;
      r *= 10.0L;
      r += *s - '0';
      s++;
      ne++;
    }
  }
  if (flags == 0)
  {
    if (sret)
      *sret = (char *)s;
    return 0.0L;
  }

  if ((*s == 'e') || (*s == 'E'))
  {
    s++;
    if (*s == '+')
      s++;
    else if (*s == '-')
    {
      s++;
      esign = -1;
    }
    while ((*s >= '0') && (*s <= '9'))
    {
      e *= 10;
      e += *s - '0';
      s++;
    }
  }
  if (esign < 0)
  {
    esign = -esign;
    e = -e;
  }
  e = e - ne;
  if (e < -4096)
  {
    /* possibly subnormal number, 10^e would overflow */
    r *= 1.0e-2048L;
    e += 2048;
  }
  if (e < 0)
  {
    e = -e;
    esign = -esign;
  }
  if (e >= 8192)
    e = 8191;
  if (e)
  {
    double d = 1.0L;
    l2powm1 = 0;
    while (e)
    {
      if (e & 1)
    d *= powten[l2powm1];
      e >>= 1;
      l2powm1++;
    }
    if (esign > 0)
      r *= d;
    else
      r /= d;
  }
  if (sret)
    *sret = (char *)s;
  return r * sign;

  return 0;
}