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/* See LICENSE file for copyright and license details. */
#include "internals.h"
static inline void
zsqr_impl_single_char(z_t a, z_t b)
{
ENSURE_SIZE(a, 1);
a->used = 1;
a->chars[0] = b->chars[0] * b->chars[0];
SET_SIGNUM(a, 1);
}
static void
zsqr_impl(z_t a, z_t b)
{
/*
* Karatsuba algorithm, optimised for equal factors.
*/
z_t z0, z1, z2, high, low;
size_t bits;
zahl_char_t auxchars[3];
bits = zbits(b);
if (bits <= BITS_PER_CHAR / 2) {
zsqr_impl_single_char(a, b);
return;
}
bits >>= 1;
zinit(z0);
zinit(z1);
zinit(z2);
if (bits < BITS_PER_CHAR) {
low->chars = auxchars;
high->chars = auxchars + 1;
zsplit_fast_small_tainted(high, low, b, bits);
} else {
bits &= ~(BITS_PER_CHAR - 1);
zsplit_fast_large_taint(high, low, b, bits);
}
zsqr_impl(z2, high);
if (unlikely(zzero(low))) {
SET_SIGNUM(z0, 0);
SET_SIGNUM(z1, 0);
} else {
zsqr_impl(z0, low);
zmul(z1, low, high);
}
zlsh(z1, z1, bits + 1);
bits <<= 1;
zlsh(a, z2, bits);
zadd_unsigned_assign(a, z1);
zadd_unsigned_assign(a, z0);
zfree(z0);
zfree(z1);
zfree(z2);
}
void
zsqr(z_t a, z_t b)
{
if (unlikely(zzero(b))) {
SET_SIGNUM(a, 0);
} else {
zsqr_impl(a, b);
SET_SIGNUM(a, 1);
}
}
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