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/* See LICENSE file for copyright and license details. */
#include "internals.h"
void
zsub_unsigned(z_t a, z_t b, z_t c)
{
zahl_char_t carry[] = {0, 0};
zahl_char_t *s;
size_t i, n;
int magcmp;
if (zzero(b)) {
zabs(a, c);
zneg(a, a);
return;
} else if (zzero(c)) {
zabs(a, b);
return;
} else if (a == b || a == c) {
/* TODO This should not be necessary. */
z_t tb, tc;
zinit(tb);
zinit(tc);
zset(tb, b);
zset(tc, c);
zsub_unsigned(a, tb, tc);
zfree(tb);
zfree(tc);
return;
}
magcmp = zcmpmag(b, c);
if (magcmp <= 0) {
if (magcmp == 0) {
SET_SIGNUM(a, 0);
return;
}
SET(a, c);
n = MIN(a->used, b->used);
s = b->chars;
} else {
SET(a, b);
n = MIN(a->used, c->used);
s = c->chars;
}
for (i = 0; i < n; i++) {
carry[~i & 1] = carry[i & 1] ? (a->chars[i] <= s[i]) : (a->chars[i] < s[i]);
a->chars[i] -= s[i];
a->chars[i] -= carry[i & 1];
}
if (carry[i & 1]) {
while (!a->chars[i])
a->chars[i++] = ZAHL_CHAR_MAX;
a->chars[i] -= 1;
}
SET_SIGNUM(a, magcmp);
}
void
zsub(z_t a, z_t b, z_t c)
{
if (b == c) {
SET_SIGNUM(a, 0);
} else if (zzero(b)) {
zneg(a, c);
} else if (zzero(c)) {
SET(a, b);
} else if ((zsignum(b) | zsignum(c)) < 0) {
if (zsignum(b) < 0) {
if (zsignum(c) < 0) {
zsub_unsigned(a, c, b);
} else {
zadd_unsigned(a, b, c);
SET_SIGNUM(a, -zsignum(a));
}
} else {
zadd_unsigned(a, b, c);
}
} else {
zsub_unsigned(a, b, c);
}
}
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