107 lines
2.6 KiB
C
107 lines
2.6 KiB
C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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* LibTomMath is library that provides for multiple-precision
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* integer arithmetic as well as number theoretic functionality.
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*
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* The library is designed directly after the MPI library by
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* Michael Fromberger but has been written from scratch with
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://libtommath.iahu.ca
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*/
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#include <tommath.h>
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/* Karatsuba squaring, computes b = a*a using three half size squarings
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*
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* See comments of mp_karatsuba_mul for details. It is essentially the same algorithm
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* but merely tuned to perform recursive squarings.
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*/
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int
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mp_karatsuba_sqr (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, err, x;
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err = MP_MEM;
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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 / 2;
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/* init copy all the temps */
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if (mp_init_size (&x0, B) != MP_OKAY)
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goto ERR;
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if (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 (mp_init (&t1) != MP_OKAY)
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goto X1;
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if (mp_init (&t2) != MP_OKAY)
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goto T1;
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if (mp_init (&x0x0) != MP_OKAY)
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goto T2;
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if (mp_init (&x1x1) != MP_OKAY)
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goto X0X0;
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/* now shift the digits */
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for (x = 0; x < B; x++) {
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x0.dp[x] = a->dp[x];
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}
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for (x = B; x < a->used; x++) {
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x1.dp[x - B] = a->dp[x];
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}
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x0.used = B;
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x1.used = a->used - B;
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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 (mp_sqr (&x0, &x0x0) != MP_OKAY)
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goto X1X1; /* x0x0 = x0*x0 */
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if (mp_sqr (&x1, &x1x1) != MP_OKAY)
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goto X1X1; /* x1x1 = x1*x1 */
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/* now calc x1-x0 and y1-y0 */
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if (mp_sub (&x1, &x0, &t1) != MP_OKAY)
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goto X1X1; /* t1 = x1 - x0 */
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if (mp_sqr (&t1, &t1) != MP_OKAY)
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goto X1X1; /* t1 = (x1 - x0) * (y1 - y0) */
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/* add x0y0 */
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if (mp_add (&x0x0, &x1x1, &t2) != MP_OKAY)
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goto X1X1; /* t2 = x0y0 + x1y1 */
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if (mp_sub (&t2, &t1, &t1) != MP_OKAY)
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goto X1X1; /* t1 = x0y0 + x1y1 - (x1-x0)*(y1-y0) */
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/* shift by B */
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if (mp_lshd (&t1, B) != MP_OKAY)
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goto X1X1; /* t1 = (x0y0 + x1y1 - (x1-x0)*(y1-y0))<<B */
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if (mp_lshd (&x1x1, B * 2) != MP_OKAY)
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goto X1X1; /* x1y1 = x1y1 << 2*B */
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if (mp_add (&x0x0, &t1, &t1) != MP_OKAY)
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goto X1X1; /* t1 = x0y0 + t1 */
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if (mp_add (&t1, &x1x1, b) != MP_OKAY)
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goto X1X1; /* t1 = x0y0 + t1 + x1y1 */
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err = MP_OKAY;
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X1X1:mp_clear (&x1x1);
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X0X0:mp_clear (&x0x0);
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T2:mp_clear (&t2);
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T1:mp_clear (&t1);
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X1:mp_clear (&x1);
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X0:mp_clear (&x0);
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ERR:
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return err;
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}
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