70 lines
1.9 KiB
C
70 lines
1.9 KiB
C
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#include "tommath_private.h"
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#ifdef BN_S_MP_SQR_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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/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
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mp_err s_mp_sqr(const mp_int *a, mp_int *b)
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{
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mp_int t;
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int ix, iy, pa;
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mp_err err;
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mp_word r;
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mp_digit u, tmpx, *tmpt;
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pa = a->used;
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if ((err = mp_init_size(&t, (2 * pa) + 1)) != MP_OKAY) {
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return err;
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}
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/* default used is maximum possible size */
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t.used = (2 * pa) + 1;
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for (ix = 0; ix < pa; ix++) {
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/* first calculate the digit at 2*ix */
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/* calculate double precision result */
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r = (mp_word)t.dp[2*ix] +
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((mp_word)a->dp[ix] * (mp_word)a->dp[ix]);
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/* store lower part in result */
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t.dp[ix+ix] = (mp_digit)(r & (mp_word)MP_MASK);
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/* get the carry */
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u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
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/* left hand side of A[ix] * A[iy] */
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tmpx = a->dp[ix];
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/* alias for where to store the results */
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tmpt = t.dp + ((2 * ix) + 1);
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for (iy = ix + 1; iy < pa; iy++) {
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/* first calculate the product */
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r = (mp_word)tmpx * (mp_word)a->dp[iy];
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/* now calculate the double precision result, note we use
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* addition instead of *2 since it's easier to optimize
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*/
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r = (mp_word)*tmpt + r + r + (mp_word)u;
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/* store lower part */
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*tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
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/* get carry */
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u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
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}
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/* propagate upwards */
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while (u != 0uL) {
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r = (mp_word)*tmpt + (mp_word)u;
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*tmpt++ = (mp_digit)(r & (mp_word)MP_MASK);
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u = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
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}
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}
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mp_clamp(&t);
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mp_exch(&t, b);
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mp_clear(&t);
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return MP_OKAY;
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}
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#endif
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