85 lines
1.8 KiB
C
85 lines
1.8 KiB
C
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#include "tommath_private.h"
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#ifdef MP_DIV_D_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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/* single digit division (based on routine from MPI) */
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mp_err mp_div_d(const mp_int *a, mp_digit b, mp_int *c, mp_digit *d)
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{
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mp_int q;
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mp_word w;
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mp_err err;
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int ix;
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/* cannot divide by zero */
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if (b == 0u) {
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return MP_VAL;
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}
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/* quick outs */
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if ((b == 1u) || mp_iszero(a)) {
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if (d != NULL) {
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*d = 0;
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}
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if (c != NULL) {
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return mp_copy(a, c);
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}
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return MP_OKAY;
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}
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/* power of two ? */
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if (MP_HAS(MP_DIV_2) && (b == 2u)) {
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if (d != NULL) {
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*d = mp_isodd(a) ? 1u : 0u;
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}
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return (c == NULL) ? MP_OKAY : mp_div_2(a, c);
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}
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if (MP_HAS(MP_DIV_2D) && MP_IS_2EXPT(b)) {
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ix = 1;
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while ((ix < MP_DIGIT_BIT) && (b != (((mp_digit)1)<<ix))) {
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ix++;
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}
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if (d != NULL) {
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*d = a->dp[0] & (((mp_digit)1<<(mp_digit)ix) - 1uL);
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}
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return (c == NULL) ? MP_OKAY : mp_div_2d(a, ix, c, NULL);
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}
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/* three? */
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if (MP_HAS(S_MP_DIV_3) && (b == 3u)) {
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return s_mp_div_3(a, c, d);
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}
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/* no easy answer [c'est la vie]. Just division */
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if ((err = mp_init_size(&q, a->used)) != MP_OKAY) {
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return err;
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}
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q.used = a->used;
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q.sign = a->sign;
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w = 0;
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for (ix = a->used; ix --> 0;) {
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mp_digit t = 0;
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w = (w << (mp_word)MP_DIGIT_BIT) | (mp_word)a->dp[ix];
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if (w >= b) {
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t = (mp_digit)(w / b);
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w -= (mp_word)t * (mp_word)b;
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}
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q.dp[ix] = t;
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}
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if (d != NULL) {
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*d = (mp_digit)w;
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}
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if (c != NULL) {
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mp_clamp(&q);
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mp_exch(&q, c);
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}
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mp_clear(&q);
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return MP_OKAY;
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}
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#endif
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