## File: bn_mp_karatsuba_sqr.c

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libtommath 1.1.0-3
 `123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124` ``````#include "tommath_private.h" #ifdef BN_MP_KARATSUBA_SQR_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * SPDX-License-Identifier: Unlicense */ /* Karatsuba squaring, computes b = a*a using three * half size squarings * * See comments of karatsuba_mul for details. It * is essentially the same algorithm but merely * tuned to perform recursive squarings. */ int mp_karatsuba_sqr(const mp_int *a, mp_int *b) { 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; 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))< master, tag: v1.1.0 */ /* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */ /* commit time: 2019-01-28 20:32:32 +0100 */ ``````