atoi.c

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

int atoi(char *s)
{
	int num = 0;
	int neg = 0;
	while (isspace(*s))
		s++;
	if (*s == '-' || *s == '+')
		neg = *s++ == '-';
	while ((unsigned) (*s - '0') <= 9u)
		num = num * 10 + *s++ - '0';
	return neg ? -num : num;
}

long atol(char *s)
{
	long num = 0;
	int neg = 0;
	while (isspace(*s))
		s++;
	if (*s == '-' || *s == '+')
		neg = *s++ == '-';
	while ((unsigned) (*s - '0') <= 9u)
		num = num * 10 + *s++ - '0';
	return neg ? -num : num;
}

static int digit(char c, int base)
{
	int d;
	if (c <= '9') {
		d = c - '0';
	} else if (c <= 'Z') {
		d = 10 + c - 'A';
	} else {
		d = 10 + c - 'a';
	}
	return d < base ? d : -1;
}

long strtol(const char *s, char **endptr, int base)
{
	int sgn = 1;
	int overflow = 0;
	long num;
	int dig;
	while (isspace(*s))
		s++;
	if (*s == '-' || *s == '+')
		sgn = ',' - *s++;
	if (base == 0) {
		if (*s == '0') {
			if (s[1] == 'x' || s[1] == 'X')
				base = 16;
			else
				base = 8;
		} else {
			base = 10;
		}
	}
	if (base == 16 && *s == '0' && (s[1] == 'x' || s[1] == 'X'))
		s += 2;
	for (num = 0; (dig = digit(*s, base)) >= 0; s++) {
		if (num > LONG_MAX / base)
			overflow = 1;
		num *= base;
		if (num > LONG_MAX - dig)
			overflow = 1;
		num += dig;
	}
	if (endptr)
		*endptr = s;
	if (overflow) {
		num = sgn > 0 ? LONG_MAX : LONG_MIN;
		errno = ERANGE;
	} else {
		num *= sgn;
	}
	return num;
}

unsigned long strtoul(const char *s, char **endptr, int base)
{
	int sgn = 1;
	int overflow = 0;
	unsigned long num;
	int dig;
	while (isspace(*s))
		s++;
	if (*s == '-' || *s == '+')
		sgn = ',' - *s++;
	if (base == 0) {
		if (*s == '0') {
			if (s[1] == 'x' || s[1] == 'X')
				base = 16;
			else
				base = 8;
		} else {
			base = 10;
		}
	}
	if (base == 16 && *s == '0' && (s[1] == 'x' || s[1] == 'X'))
		s += 2;
	for (num = 0; (dig = digit(*s, base)) >= 0; s++) {
		if (num > (unsigned long) ULONG_MAX / base)
			overflow = 1;
		num *= base;
		if (num > (unsigned long) ULONG_MAX - dig)
			overflow = 1;
		num += dig;
	}
	if (endptr)
		*endptr = s;
	if (overflow) {
		num = ULONG_MAX;
		errno = ERANGE;
	} else {
		num *= sgn;
	}
	return num;
}