GopherProxy

	zmodpow.c - libzahl - big integer library
	git clone git://git.suckless.org/libzahl
	Log
	Files
	Refs
	README
	LICENSE
	---
	zmodpow.c (1152B)
	---
	1 /* See LICENSE file for copyright and license details. */
	2 #include "internals.h"
	3
	4 #define tb libzahl_tmp_pow_b
	5 #define tc libzahl_tmp_pow_c
	6 #define td libzahl_tmp_pow_d
	7
	8
	9 void
	10 zmodpow(z_t a, z_t b, z_t c, z_t d)
	11 {
	12 size_t i, j, n, bits;
	13 zahl_char_t x;
	14
	15 /* TODO use zmodpowu when possible */
	16
	17 if (unlikely(zsignum(c) <= 0)) {
	18 if (zzero(c)) {
	19 if (check(zzero(b)))
	20 libzahl_failure(-ZERROR_0_POW_0);
	21 else if (check(zzero(d)))
	22 libzahl_failure(-ZERROR_DIV_0);
	23 zsetu(a, 1);
	24 } else if (check(zzero1(b, d))) {
	25 libzahl_failure(-ZERROR_DIV_0);
	26 } else {
	27 SET_SIGNUM(a, 0);
	28 }
	29 return;
	30 } else if (check(zzero(d))) {
	31 libzahl_failure(-ZERROR_DIV_0);
	32 } else if (unlikely(zzero(b))) {
	33 SET_SIGNUM(a, 0);
	34 return;
	35 }
	36
	37 bits = zbits(c);
	38 n = FLOOR_BITS_TO_CHARS(bits);
	39
	40 zmod(tb, b, d);
	41 zset(tc, c);
	42 zset(td, d);
	43 zsetu(a, 1);
	44
	45 for (i = 0; i < n; i++) { /* Remember, n is floored. */
	46 x = tc->chars[i];
	47 for (j = BITS_PER_CHAR; j--; x >>= 1) {
	48 if (x & 1)
	49 zmodmul(a, a, tb, td);
	50 zmodsqr(tb, tb, td);
	51 }
	52 }
	53 x = tc->chars[i];
	54 for (; x; x >>= 1) {
	55 if (x & 1)
	56 zmodmul(a, a, tb, td);
	57 zmodsqr(tb, tb, td);
	58 }
	59 }