strtoul.c

AVR-GCC 自带库的原码

#include <ctype.h>
#include <stdlib.h>
#include <errno.h>

unsigned long strtoul(CONST char *s, char **end, int base)
	{
	int endchar;
	int enddigit;
	unsigned long oldval;
	unsigned long val = 0;
	
	while (isspace(*s))
		s++;
	if (*s == 0 || !(base == 0 || (1 < base && base <= 36)))
		{
		if (end)
			*end = (char *)s;
		return 0;
		}
	if (*s == '+')
		s++;
	if (s[0] == '0' && (s[1] == 'X' || s[1] == 'x') && 
		(base == 16 || base == 0))
		{
		base = 16;
		s += 2;
		}
	if (base == 0)
		base = (*s == '0') ? 8 : 10;
	enddigit = (base >= 10) ? '9': base - 1 + '0';
	if (base > 10) 
		endchar = base - 11 + 'a';
	for ( ; *s; s++)
		{
		int c;
		
		if (isdigit(*s) && *s <= enddigit)
			c = *s - '0';
		else if (base > 10 && (c = tolower(*s)) >= 'a' && c <= endchar)
			c = c - 'a' + 10;
		else
			break;

		oldval = val;
		val = val * base + c;
		if (val < oldval)
			{
			errno = ERANGE;
			return ULONG_MAX;
			}
		}
	if (end)
		*end = (char *)s;
	return val;
	}