strtod.c

来自「用于嵌入式Linux系统的标准C的库函数」· C语言 代码 · 共 732 行 · 第 1/2 页

/*
FUNCTION
        <<strtod>>, <<strtof>>---string to double or float

INDEX
	strtod
INDEX
	_strtod_r
INDEX
	strtof

ANSI_SYNOPSIS
        #include <stdlib.h>
        double strtod(const char *<[str]>, char **<[tail]>);
        float strtof(const char *<[str]>, char **<[tail]>);

        double _strtod_r(void *<[reent]>, 
                         const char *<[str]>, char **<[tail]>);

TRAD_SYNOPSIS
        #include <stdlib.h>
        double strtod(<[str]>,<[tail]>)
        char *<[str]>;
        char **<[tail]>;

        float strtof(<[str]>,<[tail]>)
        char *<[str]>;
        char **<[tail]>;

        double _strtod_r(<[reent]>,<[str]>,<[tail]>)
	char *<[reent]>;
        char *<[str]>;
        char **<[tail]>;

DESCRIPTION
	The function <<strtod>> parses the character string <[str]>,
	producing a substring which can be converted to a double
	value.  The substring converted is the longest initial
	subsequence of <[str]>, beginning with the first
	non-whitespace character, that has the format:
	.[+|-]<[digits]>[.][<[digits]>][(e|E)[+|-]<[digits]>] 
	The substring contains no characters if <[str]> is empty, consists
	entirely of whitespace, or if the first non-whitespace
	character is something other than <<+>>, <<->>, <<.>>, or a
	digit. If the substring is empty, no conversion is done, and
	the value of <[str]> is stored in <<*<[tail]>>>.  Otherwise,
	the substring is converted, and a pointer to the final string
	(which will contain at least the terminating null character of
	<[str]>) is stored in <<*<[tail]>>>.  If you want no
	assignment to <<*<[tail]>>>, pass a null pointer as <[tail]>.
	<<strtof>> is identical to <<strtod>> except for its return type.

	This implementation returns the nearest machine number to the
	input decimal string.  Ties are broken by using the IEEE
	round-even rule.

	The alternate function <<_strtod_r>> is a reentrant version.
	The extra argument <[reent]> is a pointer to a reentrancy structure.

RETURNS
	<<strtod>> returns the converted substring value, if any.  If
	no conversion could be performed, 0 is returned.  If the
	correct value is out of the range of representable values,
	plus or minus <<HUGE_VAL>> is returned, and <<ERANGE>> is
	stored in errno. If the correct value would cause underflow, 0
	is returned and <<ERANGE>> is stored in errno.

Supporting OS subroutines required: <<close>>, <<fstat>>, <<isatty>>,
<<lseek>>, <<read>>, <<sbrk>>, <<write>>.
*/

/****************************************************************
 *
 * The author of this software is David M. Gay.
 *
 * Copyright (c) 1991 by AT&T.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose without fee is hereby granted, provided that this entire notice
 * is included in all copies of any software which is or includes a copy
 * or modification of this software and in all copies of the supporting
 * documentation for such software.
 *
 * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHOR NOR AT&T MAKES ANY
 * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
 * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
 *
 ***************************************************************/

/* Please send bug reports to
	David M. Gay
	AT&T Bell Laboratories, Room 2C-463
	600 Mountain Avenue
	Murray Hill, NJ 07974-2070
	U.S.A.
	[e-mail] or research!dmg
 */

#include <_ansi.h>
#include <reent.h>
#include <string.h>
#include "mprec.h"

double
_DEFUN (_strtod_r, (ptr, s00, se),
	struct _reent *ptr _AND
	_CONST char *s00 _AND
	char **se)
{
  int bb2, bb5, bbe, bd2, bd5, bbbits, bs2, c, dsign, e1, esign, i, j,
    k, nd, nd0, nf, nz, nz0, sign;
  long e;
  _CONST char *s, *s0, *s1;
  double aadj, aadj1, adj;
  long L;
  unsigned long z;
  __ULong y;
  union double_union rv, rv0;

  _Bigint *bb, *bb1, *bd, *bd0, *bs, *delta;
  sign = nz0 = nz = 0;
  rv.d = 0.;
  for (s = s00;; s++)
    switch (*s)
      {
      case '-':
	sign = 1;
	/* no break */
      case '+':
	if (*++s)
	  goto break2;
	/* no break */
      case 0:
	s = s00;
	goto ret;
      case '\t':
      case '\n':
      case '\v':
      case '\f':
      case '\r':
      case ' ':
	continue;
      default:
	goto break2;
      }
break2:
  if (*s == '0')
    {
      nz0 = 1;
      while (*++s == '0');
      if (!*s)
	goto ret;
    }
  s0 = s;
  y = z = 0;
  for (nd = nf = 0; (c = *s) >= '0' && c <= '9'; nd++, s++)
    if (nd < 9)
      y = 10 * y + c - '0';
    else if (nd < 16)
      z = 10 * z + c - '0';
  nd0 = nd;
  if (c == '.')
    {
      c = *++s;
      if (!nd)
	{
	  for (; c == '0'; c = *++s)
	    nz++;
	  if (c > '0' && c <= '9')
	    {
	      s0 = s;
	      nf += nz;
	      nz = 0;
	      goto have_dig;
	    }
	  goto dig_done;
	}
      for (; c >= '0' && c <= '9'; c = *++s)
	{
	have_dig:
	  nz++;
	  if (c -= '0')
	    {
	      nf += nz;
	      for (i = 1; i < nz; i++)
		if (nd++ < 9)
		  y *= 10;
		else if (nd <= DBL_DIG + 1)
		  z *= 10;
	      if (nd++ < 9)
		y = 10 * y + c;
	      else if (nd <= DBL_DIG + 1)
		z = 10 * z + c;
	      nz = 0;
	    }
	}
    }
dig_done:
  e = 0;
  if (c == 'e' || c == 'E')
    {
      if (!nd && !nz && !nz0)
	{
	  s = s00;
	  goto ret;
	}
      s00 = s;
      esign = 0;
      switch (c = *++s)
	{
	case '-':
	  esign = 1;
	case '+':
	  c = *++s;
	}
      if (c >= '0' && c <= '9')
	{
	  while (c == '0')
	    c = *++s;
	  if (c > '0' && c <= '9')
	    {
	      e = c - '0';
	      s1 = s;
	      while ((c = *++s) >= '0' && c <= '9')
		e = 10 * e + c - '0';
	      if (s - s1 > 8)
		/* Avoid confusion from exponents
		 * so large that e might overflow.
		 */
		e = 9999999L;
	      if (esign)
		e = -e;
	    }
	  else
	    e = 0;
	}
      else
	s = s00;
    }
  if (!nd)
    {
      if (!nz && !nz0)
	s = s00;
      goto ret;
    }
  e1 = e -= nf;

  /* Now we have nd0 digits, starting at s0, followed by a
   * decimal point, followed by nd-nd0 digits.  The number we're
   * after is the integer represented by those digits times
   * 10**e */

  if (!nd0)
    nd0 = nd;
  k = nd < DBL_DIG + 1 ? nd : DBL_DIG + 1;
  rv.d = y;
  if (k > 9)
    rv.d = tens[k - 9] * rv.d + z;
  bd0 = 0;
  if (nd <= DBL_DIG
#ifndef RND_PRODQUOT
      && FLT_ROUNDS == 1
#endif
    )
    {
      if (!e)
	goto ret;
      if (e > 0)
	{
	  if (e <= Ten_pmax)
	    {
#ifdef VAX
	      goto vax_ovfl_check;
#else
	      /* rv.d = */ rounded_product (rv.d, tens[e]);
	      goto ret;
#endif
	    }
	  i = DBL_DIG - nd;
	  if (e <= Ten_pmax + i)
	    {
	      /* A fancier test would sometimes let us do
				 * this for larger i values.
				 */
	      e -= i;
	      rv.d *= tens[i];
#ifdef VAX
	      /* VAX exponent range is so narrow we must
	       * worry about overflow here...
	       */
	    vax_ovfl_check:
	      word0 (rv) -= P * Exp_msk1;
	      /* rv.d = */ rounded_product (rv.d, tens[e]);
	      if ((word0 (rv) & Exp_mask)
		  > Exp_msk1 * (DBL_MAX_EXP + Bias - 1 - P))
		goto ovfl;
	      word0 (rv) += P * Exp_msk1;
#else
	      /* rv.d = */ rounded_product (rv.d, tens[e]);
#endif
	      goto ret;
	    }
	}
#ifndef Inaccurate_Divide
      else if (e >= -Ten_pmax)
	{
	  /* rv.d = */ rounded_quotient (rv.d, tens[-e]);
	  goto ret;
	}
#endif
    }
  e1 += nd - k;

  /* Get starting approximation = rv.d * 10**e1 */

  if (e1 > 0)
    {
      if ((i = e1 & 15) != 0)
	rv.d *= tens[i];
      if (e1 &= ~15)
	{
	  if (e1 > DBL_MAX_10_EXP)
	    {
	    ovfl:
	      ptr->_errno = ERANGE;
#ifdef _HAVE_STDC
	      rv.d = HUGE_VAL;
#else
	      /* Can't trust HUGE_VAL */
#ifdef IEEE_Arith
	      word0 (rv) = Exp_mask;
#ifndef _DOUBLE_IS_32BITS
	      word1 (rv) = 0;
#endif
#else
	      word0 (rv) = Big0;
#ifndef _DOUBLE_IS_32BITS
	      word1 (rv) = Big1;
#endif
#endif
#endif
	      if (bd0)
		goto retfree;
	      goto ret;
	    }
	  if (e1 >>= 4)
	    {
	      for (j = 0; e1 > 1; j++, e1 >>= 1)
		if (e1 & 1)
		  rv.d *= bigtens[j];
	      /* The last multiplication could overflow. */
	      word0 (rv) -= P * Exp_msk1;
	      rv.d *= bigtens[j];
	      if ((z = word0 (rv) & Exp_mask)
		  > Exp_msk1 * (DBL_MAX_EXP + Bias - P))
		goto ovfl;
	      if (z > Exp_msk1 * (DBL_MAX_EXP + Bias - 1 - P))
		{
		  /* set to largest number */
		  /* (Can't trust DBL_MAX) */
		  word0 (rv) = Big0;
#ifndef _DOUBLE_IS_32BITS
		  word1 (rv) = Big1;
#endif
		}