93 lines
2.5 KiB
C
93 lines
2.5 KiB
C
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#include "tommath_private.h"
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#ifdef S_MP_SQR_KARATSUBA_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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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 mul_karatsuba for details. It
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* is essentially the same algorithm but merely
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* tuned to perform recursive squarings.
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*/
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mp_err s_mp_sqr_karatsuba(const mp_int *a, mp_int *b)
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{
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mp_int x0, x1, t1, t2, x0x0, x1x1;
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int B;
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mp_err err;
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/* min # of digits */
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B = a->used;
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/* now divide in two */
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B = B >> 1;
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/* init copy all the temps */
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if ((err = mp_init_size(&x0, B)) != MP_OKAY)
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goto LBL_ERR;
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if ((err = mp_init_size(&x1, a->used - B)) != MP_OKAY)
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goto X0;
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/* init temps */
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if ((err = mp_init_size(&t1, a->used * 2)) != MP_OKAY)
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goto X1;
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if ((err = mp_init_size(&t2, a->used * 2)) != MP_OKAY)
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goto T1;
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if ((err = mp_init_size(&x0x0, B * 2)) != MP_OKAY)
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goto T2;
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if ((err = mp_init_size(&x1x1, (a->used - B) * 2)) != MP_OKAY)
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goto X0X0;
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/* now shift the digits */
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x0.used = B;
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x1.used = a->used - B;
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s_mp_copy_digs(x0.dp, a->dp, x0.used);
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s_mp_copy_digs(x1.dp, a->dp + B, x1.used);
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mp_clamp(&x0);
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/* now calc the products x0*x0 and x1*x1 */
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if ((err = mp_sqr(&x0, &x0x0)) != MP_OKAY)
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goto X1X1; /* x0x0 = x0*x0 */
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if ((err = mp_sqr(&x1, &x1x1)) != MP_OKAY)
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goto X1X1; /* x1x1 = x1*x1 */
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/* now calc (x1+x0)**2 */
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if ((err = s_mp_add(&x1, &x0, &t1)) != MP_OKAY)
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goto X1X1; /* t1 = x1 - x0 */
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if ((err = mp_sqr(&t1, &t1)) != MP_OKAY)
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goto X1X1; /* t1 = (x1 - x0) * (x1 - x0) */
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/* add x0y0 */
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if ((err = s_mp_add(&x0x0, &x1x1, &t2)) != MP_OKAY)
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goto X1X1; /* t2 = x0x0 + x1x1 */
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if ((err = s_mp_sub(&t1, &t2, &t1)) != MP_OKAY)
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goto X1X1; /* t1 = (x1+x0)**2 - (x0x0 + x1x1) */
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/* shift by B */
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if ((err = mp_lshd(&t1, B)) != MP_OKAY)
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goto X1X1; /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
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if ((err = mp_lshd(&x1x1, B * 2)) != MP_OKAY)
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goto X1X1; /* x1x1 = x1x1 << 2*B */
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if ((err = mp_add(&x0x0, &t1, &t1)) != MP_OKAY)
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goto X1X1; /* t1 = x0x0 + t1 */
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if ((err = mp_add(&t1, &x1x1, b)) != MP_OKAY)
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goto X1X1; /* t1 = x0x0 + t1 + x1x1 */
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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);
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LBL_ERR:
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return err;
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}
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#endif
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