forked from ibphoenix/tomsfastmath
108 lines
2.5 KiB
C
108 lines
2.5 KiB
C
/* TomsFastMath, a fast ISO C bignum library.
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*
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* This project is meant to fill in where LibTomMath
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* falls short. That is speed ;-)
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*
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* This project is public domain and free for all purposes.
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*
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* Tom St Denis, tomstdenis@iahu.ca
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*/
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#include <tfm.h>
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/* b = a*a */
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void fp_sqr(fp_int *A, fp_int *B)
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{
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int r, y, s;
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fp_int aa, bb, comp, amb, t1;
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y = A->used;
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if (y <= 48) {
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if (y <= 4) {
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fp_sqr_comba4(A,B);
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} else if (y <= 8) {
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fp_sqr_comba8(A,B);
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} else if (y <= 16 && y >= 12) {
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fp_sqr_comba16(A,B);
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#ifdef TFM_HUGE
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} else if (y <= 32 && y >= 28) {
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fp_sqr_comba32(A,B);
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#endif
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} else {
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fp_sqr_comba(A, B);
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}
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} else {
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/* do the karatsuba action
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if A = ab ||a|| = r we need to solve
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a^2*r^2 + (-(a-b)^2 + a^2 + b^2)*r + b^2
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So we solve for the three products then we form the final result with careful shifting
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and addition.
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Obvious points of optimization
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- "ac" parts can be memcpy'ed with an offset [all you have to do is zero upto the next 8 digits]
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- Similarly the "bd" parts can be memcpy'ed and zeroed to 8
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-
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*/
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/* get our value of r */
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r = y >> 1;
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/* now solve for ac */
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// fp_copy(A, &t1); fp_rshd(&t1, r);
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for (s = 0; s < A->used - r; s++) {
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t1.dp[s] = A->dp[s+r];
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}
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for (; s < FP_SIZE; s++) {
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t1.dp[s] = 0;
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}
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if (A->used >= r) {
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t1.used = A->used - r;
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} else {
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t1.used = 0;
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}
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t1.sign = A->sign;
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fp_copy(&t1, &amb);
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fp_zero(&aa);
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fp_sqr(&t1, &aa);
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/* now solve for bd */
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// fp_mod_2d(A, r * DIGIT_BIT, &t1);
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for (s = 0; s < r; s++) {
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t1.dp[s] = A->dp[s];
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}
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for (; s < FP_SIZE; s++) {
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t1.dp[s] = 0;
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}
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t1.used = r;
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fp_clamp(&t1);
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fp_sub(&amb, &t1, &amb);
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fp_zero(&bb);
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fp_sqr(&t1, &bb);
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/* now get the (a-b) term */
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fp_zero(&comp);
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fp_sqr(&amb, &comp);
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/* now solve the system, do the middle term first */
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comp.sign ^= 1;
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fp_add(&comp, &aa, &comp);
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fp_add(&comp, &bb, &comp);
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fp_lshd(&comp, r);
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/* leading term */
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fp_lshd(&aa, r+r);
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/* now sum them together */
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fp_zero(B);
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fp_add(&aa, &comp, B);
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fp_add(&bb, B, B);
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B->sign = FP_ZPOS;
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}
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}
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