tommath/bn_mp_karatsuba_sqr.c

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#include "tommath_private.h"
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#ifdef BN_MP_KARATSUBA_SQR_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
*
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* The library was designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
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* SPDX-License-Identifier: Unlicense
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*/
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/* Karatsuba squaring, computes b = a*a using three
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* half size squarings
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*
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* See comments of karatsuba_mul for details. It
* is essentially the same algorithm but merely
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* tuned to perform recursive squarings.
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*/
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int mp_karatsuba_sqr(const mp_int *a, mp_int *b)
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{
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mp_int x0, x1, t1, t2, x0x0, x1x1;
int B, err;
err = MP_MEM;
/* min # of digits */
B = a->used;
/* now divide in two */
B = B >> 1;
/* init copy all the temps */
if (mp_init_size(&x0, B) != MP_OKAY)
goto LBL_ERR;
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if (mp_init_size(&x1, a->used - B) != MP_OKAY)
goto X0;
/* init temps */
if (mp_init_size(&t1, a->used * 2) != MP_OKAY)
goto X1;
if (mp_init_size(&t2, a->used * 2) != MP_OKAY)
goto T1;
if (mp_init_size(&x0x0, B * 2) != MP_OKAY)
goto T2;
if (mp_init_size(&x1x1, (a->used - B) * 2) != MP_OKAY)
goto X0X0;
{
int x;
mp_digit *dst, *src;
src = a->dp;
/* now shift the digits */
dst = x0.dp;
for (x = 0; x < B; x++) {
*dst++ = *src++;
}
dst = x1.dp;
for (x = B; x < a->used; x++) {
*dst++ = *src++;
}
}
x0.used = B;
x1.used = a->used - B;
mp_clamp(&x0);
/* now calc the products x0*x0 and x1*x1 */
if (mp_sqr(&x0, &x0x0) != MP_OKAY)
goto X1X1; /* x0x0 = x0*x0 */
if (mp_sqr(&x1, &x1x1) != MP_OKAY)
goto X1X1; /* x1x1 = x1*x1 */
/* now calc (x1+x0)**2 */
if (s_mp_add(&x1, &x0, &t1) != MP_OKAY)
goto X1X1; /* t1 = x1 - x0 */
if (mp_sqr(&t1, &t1) != MP_OKAY)
goto X1X1; /* t1 = (x1 - x0) * (x1 - x0) */
/* add x0y0 */
if (s_mp_add(&x0x0, &x1x1, &t2) != MP_OKAY)
goto X1X1; /* t2 = x0x0 + x1x1 */
if (s_mp_sub(&t1, &t2, &t1) != MP_OKAY)
goto X1X1; /* t1 = (x1+x0)**2 - (x0x0 + x1x1) */
/* shift by B */
if (mp_lshd(&t1, B) != MP_OKAY)
goto X1X1; /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
if (mp_lshd(&x1x1, B * 2) != MP_OKAY)
goto X1X1; /* x1x1 = x1x1 << 2*B */
if (mp_add(&x0x0, &t1, &t1) != MP_OKAY)
goto X1X1; /* t1 = x0x0 + t1 */
if (mp_add(&t1, &x1x1, b) != MP_OKAY)
goto X1X1; /* t1 = x0x0 + t1 + x1x1 */
err = MP_OKAY;
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X1X1:
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mp_clear(&x1x1);
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X0X0:
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mp_clear(&x0x0);
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T2:
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mp_clear(&t2);
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T1:
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mp_clear(&t1);
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X1:
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mp_clear(&x1);
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X0:
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mp_clear(&x0);
LBL_ERR:
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return err;
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}
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#endif
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/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */