Пример #1
0
static void two_complement_bitop(mp_int *a, mp_int *b, mp_int *c,
        int (*mp_bitop)(mp_int *, mp_int *, mp_int *)) {
    mp_int d;
    if (SIGN(a) ^ SIGN(b)) {
        /* exactly one of them is negative, so need to perform
         * some magic. tommath stores a sign bit, but Perl 6 expects
         * 2's complement */
        mp_init(&d);
        if (MP_NEG == SIGN(a)) {
            grow_and_negate(a, USED(b), &d);
            mp_bitop(&d, b, c);
        } else {
            grow_and_negate(b, USED(a), &d);
            mp_bitop(a, &d, c);
        }
        if (DIGIT(c, USED(c) - 1) & ((mp_digit)1<<(mp_digit)(DIGIT_BIT - 1))) {
            grow_and_negate(c, c->used, &d);
            mp_copy(&d, c);
            mp_neg(c, c);
        }
        mp_clear(&d);
    } else {
        mp_bitop(a, b, c);
    }

}
Пример #2
0
static void two_complement_bitop(mp_int *a, mp_int *b, mp_int *c,
				 int (*mp_bitop)(mp_int *, mp_int *, mp_int *)) {

    mp_int d;
    mp_int e;
    mp_int *f;
    mp_int *g;

    f = a;
    g = b;
    if (MP_NEG == SIGN(a)) {
        mp_init(&d);
        grow_and_negate(a, USED(b), &d);
        f = &d;
    }
    if (MP_NEG == SIGN(b)) {
        mp_init(&e);
        grow_and_negate(b, USED(a), &e);
        g = &e;
    }
    /* f and g now guaranteed to each point to positive bigints containing
     * a 2s compliment representation of the values in a and b.  If either
     * a or b was negative, the representation is one tomath "digit" longer
     * than it need be and sign extended.
     */
    mp_bitop(f, g, c);
    if (f == &d) mp_clear(&d);
    if (g == &e) mp_clear(&e);
    /* Use the fact that tomath clamps to detect results that should be
     * signed.  If we created extra tomath "digits" and they resulted in
     * sign bits of 0, they have been clamped away.  If the resulting sign
     * bits were 1, they remain, and c will have more digits than either of
     * original operands.  Note this only works because we do not
     * support NOR/NAND/NXOR, and so two zero sign bits can never create 1s.
     */
    if (USED(c) > MAX(USED(a),USED(b))) {
        int i;
        for (i = 0; i < USED(c); i++) {
            DIGIT(c, i) = (~DIGIT(c, i)) & MP_MASK;
        }
        mp_add_d(c, 1, c);
	mp_neg(c, c);
    }
}