lib/strtol.c

/* Copyright (C) 1991, 1992, 1994, 1995 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If
   not, write to the Free Software Foundation, Inc., 675 Mass Ave,
   Cambridge, MA 02139, USA.  */

/* Convert NPTR to an `unsigned long int' or `long int' in base BASE.
   If BASE is 0 the base is determined by the presence of a leading
   zero, indicating octal or a leading "0x" or "0X", indicating hexadecimal.
   If BASE is < 2 or > 36, it is reset to 10.
   If ENDPTR is not NULL, a pointer to the character after the last
   one converted is stored in *ENDPTR.  */

#include "ctype.h"

int strtol (nptr, endptr, base)
const char *nptr;
char **endptr;
int base;
{
    int negative;
    register unsigned int cutoff;
    register unsigned int cutlim;
    register unsigned int i;
    register const char *s;
    register unsigned char c;
    const char *save, *end;
    int overflow;

    if (base < 0 || base == 1 || base > 36)
	base = 10;

    save = s = nptr;

    /* Skip white space.  */
    while (((unsigned char) *s) <= 32 && *s)
	++s;
    if (*s == '\0')
	goto noconv;

    /* Check for a sign.  */
    if (*s == '-') {
	negative = 1;
	++s;
    } else if (*s == '+') {
	negative = 0;
	++s;
    } else
	negative = 0;

    if ((base == 16 && s[0] == '0' && (s[1] == 'X')) || (s[1] == 'x'))
	s += 2;

    /* If BASE is zero, figure it out ourselves.  */
    if (base == 0) {
	if (*s == '0') {
	    if (s[1] == 'X' || s[1] == 'x') {
		s += 2;
		base = 16;
	    } else
		base = 8;
	} else
	    base = 10;
    }

    /* Save the pointer so we can check later if anything happened.  */
    save = s;

    end = 0;

    cutoff = 0x7FFFFFFF / (unsigned int) base;
    cutlim = 0x7FFFFFFF % (unsigned int) base;

    overflow = 0;
    i = 0;
    for (c = *s; c != '\0'; c = *++s) {
	if (s == end)
	    break;
	if (c >= '0' && c <= '9')
	    c -= '0';
	else if (c >= 'A' && c <= 'Z')
	    c = c - 'A' + 10;
	else if (c >= 'a' && c <= 'z')
	    c = c - 'a' + 10;
	else
	    break;
	if (c >= base)
	    break;
	/* Check for overflow.  */
	if (i > cutoff || (i == cutoff && c > cutlim))
	    overflow = 1;
	else {
	    i *= (unsigned int) base;
	    i += c;
	}
    }

    /* Check if anything actually happened.  */
    if (s == save)
	goto noconv;

    /* Store in ENDPTR the address of one character
       past the last character we converted.  */
    if (endptr)
	*endptr = (char *) s;

    if (overflow)
	return negative ? (int) 0x80000000 : (int) 0x7FFFFFFF;

    /* Return the result of the appropriate sign.  */
    return (negative ? -i : i);

  noconv:
    /* We must handle a special case here: the base is 0 or 16 and the
       first two characters and '0' and 'x', but the rest are no
       hexadecimal digits.  This is no error case.  We return 0 and
       ENDPTR points to the `x`.  */
    if (endptr) {
	if (save - nptr >= 2 && tolower (save[-1]) == 'x' && save[-2] == '0')
	    *endptr = (char *) &save[-1];
	else
	    /*  There was no number to convert.  */
	    *endptr = (char *) nptr;
    }

    return 0L;
}