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strtod.c

/* Copyright (C) 1991-1992, 1997, 1999, 2003, 2006, 2008-2011 Free Software
   Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>

#include <stdlib.h>

#include <ctype.h>
#include <errno.h>
#include <float.h>
#include <limits.h>
#include <math.h>
#include <stdbool.h>
#include <string.h>

#include "c-ctype.h"

#ifndef HAVE_LDEXP_IN_LIBC
#define HAVE_LDEXP_IN_LIBC 0
#endif
#ifndef HAVE_RAW_DECL_STRTOD
#define HAVE_RAW_DECL_STRTOD 0
#endif

/* Return true if C is a space in the current locale, avoiding
   problems with signed char and isspace.  */
static bool
locale_isspace (char c)
{
  unsigned char uc = c;
  return isspace (uc) != 0;
}

#if !HAVE_LDEXP_IN_LIBC
 #define ldexp dummy_ldexp
 /* A dummy definition that will never be invoked.  */
 static double ldexp (double x _GL_UNUSED, int exponent _GL_UNUSED)
 {
   abort ();
   return 0.0;
 }
#endif

/* Return X * BASE**EXPONENT.  Return an extreme value and set errno
   to ERANGE if underflow or overflow occurs.  */
static double
scale_radix_exp (double x, int radix, long int exponent)
{
  /* If RADIX == 10, this code is neither precise nor fast; it is
     merely a straightforward and relatively portable approximation.
     If N == 2, this code is precise on a radix-2 implementation,
     albeit perhaps not fast if ldexp is not in libc.  */

  long int e = exponent;

  if (HAVE_LDEXP_IN_LIBC && radix == 2)
    return ldexp (x, e < INT_MIN ? INT_MIN : INT_MAX < e ? INT_MAX : e);
  else
    {
      double r = x;

      if (r != 0)
        {
          if (e < 0)
            {
              while (e++ != 0)
                {
                  r /= radix;
                  if (r == 0 && x != 0)
                    {
                      errno = ERANGE;
                      break;
                    }
                }
            }
          else
            {
              while (e-- != 0)
                {
                  if (r < -DBL_MAX / radix)
                    {
                      errno = ERANGE;
                      return -HUGE_VAL;
                    }
                  else if (DBL_MAX / radix < r)
                    {
                      errno = ERANGE;
                      return HUGE_VAL;
                    }
                  else
                    r *= radix;
                }
            }
        }

      return r;
    }
}

/* Parse a number at NPTR; this is a bit like strtol (NPTR, ENDPTR)
   except there are no leading spaces or signs or "0x", and ENDPTR is
   nonnull.  The number uses a base BASE (either 10 or 16) fraction, a
   radix RADIX (either 10 or 2) exponent, and exponent character
   EXPCHAR.  To convert from a number of digits to a radix exponent,
   multiply by RADIX_MULTIPLIER (either 1 or 4).  */
static double
parse_number (const char *nptr,
              int base, int radix, int radix_multiplier, char expchar,
              char **endptr)
{
  const char *s = nptr;
  bool got_dot = false;
  long int exponent = 0;
  double num = 0;

  for (;; ++s)
    {
      int digit;
      if (c_isdigit (*s))
        digit = *s - '0';
      else if (base == 16 && c_isxdigit (*s))
        digit = c_tolower (*s) - ('a' - 10);
      else if (! got_dot && *s == '.')
        {
          /* Record that we have found the decimal point.  */
          got_dot = true;
          continue;
        }
      else
        /* Any other character terminates the number.  */
        break;

      /* Make sure that multiplication by base will not overflow.  */
      if (num <= DBL_MAX / base)
        num = num * base + digit;
      else
        {
          /* The value of the digit doesn't matter, since we have already
             gotten as many digits as can be represented in a `double'.
             This doesn't necessarily mean the result will overflow.
             The exponent may reduce it to within range.

             We just need to record that there was another
             digit so that we can multiply by 10 later.  */
          exponent += radix_multiplier;
        }

      /* Keep track of the number of digits after the decimal point.
         If we just divided by base here, we might lose precision.  */
      if (got_dot)
        exponent -= radix_multiplier;
    }

  if (c_tolower (*s) == expchar && ! locale_isspace (s[1]))
    {
      /* Add any given exponent to the implicit one.  */
      int save = errno;
      char *end;
      long int value = strtol (s + 1, &end, 10);
      errno = save;

      if (s + 1 != end)
        {
          /* Skip past the exponent, and add in the implicit exponent,
             resulting in an extreme value on overflow.  */
          s = end;
          exponent =
            (exponent < 0
             ? (value < LONG_MIN - exponent ? LONG_MIN : exponent + value)
             : (LONG_MAX - exponent < value ? LONG_MAX : exponent + value));
        }
    }

  *endptr = (char *) s;
  return scale_radix_exp (num, radix, exponent);
}

static double underlying_strtod (const char *, char **);

/* HP cc on HP-UX 10.20 has a bug with the constant expression -0.0.
   ICC 10.0 has a bug when optimizing the expression -zero.
   The expression -DBL_MIN * DBL_MIN does not work when cross-compiling
   to PowerPC on MacOS X 10.5.  */
#if defined __hpux || defined __sgi || defined __ICC
static double
compute_minus_zero (void)
{
  return -DBL_MIN * DBL_MIN;
}
# define minus_zero compute_minus_zero ()
#else
double minus_zero = -0.0;
#endif

/* Convert NPTR to a double.  If ENDPTR is not NULL, a pointer to the
   character after the last one used in the number is put in *ENDPTR.  */
double
strtod (const char *nptr, char **endptr)
{
  bool negative = false;

  /* The number so far.  */
  double num;

  const char *s = nptr;
  const char *end;
  char *endbuf;
  int saved_errno;

  /* Eat whitespace.  */
  while (locale_isspace (*s))
    ++s;

  /* Get the sign.  */
  negative = *s == '-';
  if (*s == '-' || *s == '+')
    ++s;

  saved_errno = errno;
  num = underlying_strtod (s, &endbuf);
  end = endbuf;

  if (c_isdigit (s[*s == '.']))
    {
      /* If a hex float was converted incorrectly, do it ourselves.
         If the string starts with "0x" but does not contain digits,
         consume the "0" ourselves.  If a hex float is followed by a
         'p' but no exponent, then adjust the end pointer.  */
      if (*s == '0' && c_tolower (s[1]) == 'x')
        {
          if (! c_isxdigit (s[2 + (s[2] == '.')]))
            end = s + 1;
          else if (end <= s + 2)
            {
              num = parse_number (s + 2, 16, 2, 4, 'p', &endbuf);
              end = endbuf;
            }
          else
            {
              const char *p = s + 2;
              while (p < end && c_tolower (*p) != 'p')
                p++;
              if (p < end && ! c_isdigit (p[1 + (p[1] == '-' || p[1] == '+')]))
                end = p;
            }
        }
      else
        {
          /* If "1e 1" was misparsed as 10.0 instead of 1.0, re-do the
             underlying strtod on a copy of the original string
             truncated to avoid the bug.  */
          const char *e = s + 1;
          while (e < end && c_tolower (*e) != 'e')
            e++;
          if (e < end && ! c_isdigit (e[1 + (e[1] == '-' || e[1] == '+')]))
            {
              char *dup = strdup (s);
              errno = saved_errno;
              if (!dup)
                {
                  /* Not really our day, is it.  Rounding errors are
                     better than outright failure.  */
                  num = parse_number (s, 10, 10, 1, 'e', &endbuf);
                }
              else
                {
                  dup[e - s] = '\0';
                  num = underlying_strtod (dup, &endbuf);
                  saved_errno = errno;
                  free (dup);
                  errno = saved_errno;
                }
              end = e;
            }
        }

      s = end;
    }

  /* Check for infinities and NaNs.  */
  else if (c_tolower (*s) == 'i'
           && c_tolower (s[1]) == 'n'
           && c_tolower (s[2]) == 'f')
    {
      s += 3;
      if (c_tolower (*s) == 'i'
          && c_tolower (s[1]) == 'n'
          && c_tolower (s[2]) == 'i'
          && c_tolower (s[3]) == 't'
          && c_tolower (s[4]) == 'y')
        s += 5;
      num = HUGE_VAL;
      errno = saved_errno;
    }
  else if (c_tolower (*s) == 'n'
           && c_tolower (s[1]) == 'a'
           && c_tolower (s[2]) == 'n')
    {
      s += 3;
      if (*s == '(')
        {
          const char *p = s + 1;
          while (c_isalnum (*p))
            p++;
          if (*p == ')')
            s = p + 1;
        }

      /* If the underlying implementation misparsed the NaN, assume
         its result is incorrect, and return a NaN.  Normally it's
         better to use the underlying implementation's result, since a
         nice implementation populates the bits of the NaN according
         to interpreting n-char-sequence as a hexadecimal number.  */
      if (s != end)
        num = NAN;
      errno = saved_errno;
    }
  else
    {
      /* No conversion could be performed.  */
      errno = EINVAL;
      s = nptr;
    }

  if (endptr != NULL)
    *endptr = (char *) s;
  /* Special case -0.0, since at least ICC miscompiles negation.  We
     can't use copysign(), as that drags in -lm on some platforms.  */
  if (!num && negative)
    return minus_zero;
  return negative ? -num : num;
}

/* The "underlying" strtod implementation.  This must be defined
   after strtod because it #undefs strtod.  */
static double
underlying_strtod (const char *nptr, char **endptr)
{
  if (HAVE_RAW_DECL_STRTOD)
    {
      /* Prefer the native strtod if available.  Usually it should
         work and it should give more-accurate results than our
         approximation.  */
      #undef strtod
      return strtod (nptr, endptr);
    }
  else
    {
      /* Approximate strtod well enough for this module.  There's no
         need to handle anything but finite unsigned decimal
         numbers with nonnull ENDPTR.  */
      return parse_number (nptr, 10, 10, 1, 'e', endptr);
    }
}

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