source: buchla-68k/libsm/strtol.c@ d10dbee

/*
   =============================================================================
        strtol.c -- convert a string of ASCII digits to a long
        Version 1 -- 1987-06-12
   =============================================================================
*/

#include "ctype.h"

#define DIGIT(x) (isdigit(x) ? (x)-'0' : islower(x) ? (x)+10-'a' : (x)+10-'A')

#define MBASE   ('z' - 'a' + 1 + 10)

int32_t strtol(int8_t *str, int8_t **ptr, int16_t base)
{
        register int32_t val;
        register int16_t c;
        int16_t xx, neg = 0;

        if (ptr != (int8_t **)0)
                *ptr = str; /* in case no number is formed */

        if (base < 0 || base > MBASE)
                return (0); /* base is invalid -- should be a fatal error */

        if (!isalnum(c = *str)) {

                while (isspace(c))
                        c = *++str;

                switch (c) {

                case '-':
                        neg++;

                case '+': /* fall-through */
                        c = *++str;
                }
        }

        if (base == 0)
                if (c != '0')
                        base = 10;
                else if (str[1] == 'x' || str[1] == 'X')
                        base = 16;
                else
                        base = 8;
        /*
                for any base > 10, the digits incrementally following
                9 are assumed to be "abc...z" or "ABC...Z"
        */

        if (!isalnum(c) || (xx = DIGIT(c)) >= base)
                return (0); /* no number formed */

        if (base == 16 && c == '0' && isxdigit(str[2]) &&
           (str[1] == 'x' || str[1] == 'X'))
                c = *(str += 2); /* skip over leading "0x" or "0X" */

        for (val = -DIGIT(c); isalnum(c = *++str) && (xx = DIGIT(c)) < base; )
                 /* accumulate neg avoids surprises near MAXLONG */
                val = base * val - xx;

        if (ptr != (int8_t **)0)
                *ptr = str;

        return (neg ? val : -val);
}