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/* See LICENSE file for copyright and license details. */
#include "internals.h"
#define tb libzahl_tmp_pow_b
#define tc libzahl_tmp_pow_c
#define td libzahl_tmp_pow_d
void
zmodpow(z_t a, z_t b, z_t c, z_t d)
{
size_t i, j, n, bits;
zahl_char_t x;
if (zsignum(c) <= 0) {
if (zzero(c)) {
if (zzero(b)) {
errno = EDOM; /* Indeterminate form: 0:th power of 0 */
FAILURE_JUMP();
}
zsetu(a, 1);
} else if (zzero(b) || zzero(d)) {
errno = EDOM; /* Undefined form: Division by 0 */
FAILURE_JUMP();
} else {
SET_SIGNUM(a, 0);
}
return;
} else if (zzero(d)) {
errno = EDOM; /* Undefined form: Division by 0 */
FAILURE_JUMP();
} else if (zzero(b)) {
SET_SIGNUM(a, 0);
return;
}
bits = zbits(c);
n = FLOOR_BITS_TO_CHARS(bits);
zmod(tb, b, d);
zset(tc, c);
zset(td, d);
zsetu(a, 1);
for (i = 0; i < n; i++) {
x = tc->chars[i];
for (j = BITS_PER_CHAR; j--; x >>= 1) {
if (x & 1)
zmodmul(a, a, tb, td);
zmodsqr(tb, tb, td);
}
}
}
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