Function regexec

v2/engine/regexp.c:795–853

- regexec - match a regexp against a string */

 - regexec - match a regexp against a string
 */
int
regexec(
    register regexp *prog,
    register const char *string )
{
    register char *s;

    /* Be paranoid... */
    if (prog == NULL || string == NULL) {
        regerror("NULL parameter");
        return(0);
    }

    /* Check validity of program. */
    if (UCHARAT(prog->program) != MAGIC) {
        regerror("corrupted program");
        return(0);
    }

    /* If there is a "must appear" string, look for it. */
    if ( prog->regmust != NULL )
    {
        s = (char *)string;
        while ( ( s = strchr( s, prog->regmust[ 0 ] ) ) != NULL )
        {
            if ( !strncmp( s, prog->regmust, prog->regmlen ) )
                break;  /* Found it. */
            ++s;
        }
        if ( s == NULL )  /* Not present. */
            return 0;
    }

    /* Mark beginning of line for ^ . */
    regbol = (char *)string;

    /* Simplest case:  anchored match need be tried only once. */
    if ( prog->reganch )
        return regtry( prog, string );

    /* Messy cases:  unanchored match. */
    s = (char *)string;
    if (prog->regstart != '\0')
        /* We know what char it must start with. */
        while ((s = strchr(s, prog->regstart)) != NULL) {
            if (regtry(prog, s))
                return(1);
            s++;
        }
    else
        /* We do not -- general case. */
        do {
            if ( regtry( prog, s ) )
                return( 1 );
        } while ( *s++ != '\0' );

    /* Failure. */
    return 0;