source: buchla-68k/libsm/strcspn.c@ c3aee8a

/*
   ============================================================================
        strcspn.c -- character scan function ala' Unix(tm)
        Version 1 -- 1987-02-11 -- D.N. Lynx Crowe

        Return the number of characters in the maximum leading segment
        of string which consists solely of characters NOT from charset.
   ============================================================================
*/

int16_t strcspn(int8_t *string, int8_t *charset)
{
        register int8_t *p, *q;
        register int16_t n = 0;

        for(q = string; *q != '\0'; ++q , ++n) {

                for(p = charset; *p != '\0' && *p != *q; ++p)
                        ;

                if(*p != '\0')
                        break;
        }

        return(n);
}