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	zmodpowu.c - libzahl - big integer library
	git clone git://git.suckless.org/libzahl
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	---
	zmodpowu.c (683B)
	---
	1 /* See LICENSE file for copyright and license details. */
	2 #include "internals.h"
	3
	4 #define tb libzahl_tmp_pow_b
	5 #define td libzahl_tmp_pow_d
	6
	7
	8 void
	9 zmodpowu(z_t a, z_t b, unsigned long long int c, z_t d)
	10 {
	11 if (unlikely(!c)) {
	12 if (check(zzero(b)))
	13 libzahl_failure(-ZERROR_0_POW_0);
	14 else if (check(zzero(d)))
	15 libzahl_failure(-ZERROR_DIV_0);
	16 else
	17 zsetu(a, 1);
	18 return;
	19 } else if (check(zzero(d))) {
	20 libzahl_failure(-ZERROR_DIV_0);
	21 } else if (unlikely(zzero(b))) {
	22 SET_SIGNUM(a, 0);
	23 return;
	24 }
	25
	26 zmod(tb, b, d);
	27 zset(td, d);
	28
	29 if (c & 1)
	30 zset(a, tb);
	31 else
	32 zsetu(a, 1);
	33 while (c >>= 1) {
	34 zmodsqr(tb, tb, td);
	35 if (c & 1)
	36 zmodmul(a, a, tb, td);
	37 }
	38 }