95 lines
2.8 KiB
C
95 lines
2.8 KiB
C
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#include "tommath_private.h"
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#ifdef MP_IS_SQUARE_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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/* Check if remainders are possible squares - fast exclude non-squares */
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static const char rem_128[128] = {
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0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1
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};
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static const char rem_105[105] = {
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0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1,
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0, 0, 1, 1, 1, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1,
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0, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1,
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1, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1,
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0, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1,
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1, 1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1, 1,
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1, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1
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};
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/* Store non-zero to ret if arg is square, and zero if not */
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mp_err mp_is_square(const mp_int *arg, bool *ret)
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{
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mp_err err;
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mp_digit c;
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mp_int t;
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uint32_t r;
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/* Default to Non-square :) */
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*ret = false;
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if (mp_isneg(arg)) {
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return MP_VAL;
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}
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if (mp_iszero(arg)) {
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*ret = true;
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return MP_OKAY;
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}
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/* First check mod 128 (suppose that MP_DIGIT_BIT is at least 7) */
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if (rem_128[127u & arg->dp[0]] == (char)1) {
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return MP_OKAY;
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}
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/* Next check mod 105 (3*5*7) */
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if ((err = mp_mod_d(arg, 105uL, &c)) != MP_OKAY) {
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return err;
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}
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if (rem_105[c] == (char)1) {
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return MP_OKAY;
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}
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if ((err = mp_init_u32(&t, 11u*13u*17u*19u*23u*29u*31u)) != MP_OKAY) {
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return err;
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}
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if ((err = mp_mod(arg, &t, &t)) != MP_OKAY) {
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goto LBL_ERR;
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}
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r = mp_get_u32(&t);
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/* Check for other prime modules, note it's not an ERROR but we must
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* free "t" so the easiest way is to goto LBL_ERR. We know that err
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* is already equal to MP_OKAY from the mp_mod call
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*/
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if (((1uL<<(r%11uL)) & 0x5C4uL) != 0uL) goto LBL_ERR;
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if (((1uL<<(r%13uL)) & 0x9E4uL) != 0uL) goto LBL_ERR;
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if (((1uL<<(r%17uL)) & 0x5CE8uL) != 0uL) goto LBL_ERR;
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if (((1uL<<(r%19uL)) & 0x4F50CuL) != 0uL) goto LBL_ERR;
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if (((1uL<<(r%23uL)) & 0x7ACCA0uL) != 0uL) goto LBL_ERR;
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if (((1uL<<(r%29uL)) & 0xC2EDD0CuL) != 0uL) goto LBL_ERR;
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if (((1uL<<(r%31uL)) & 0x6DE2B848uL) != 0uL) goto LBL_ERR;
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/* Final check - is sqr(sqrt(arg)) == arg ? */
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if ((err = mp_sqrt(arg, &t)) != MP_OKAY) {
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goto LBL_ERR;
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}
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if ((err = mp_sqr(&t, &t)) != MP_OKAY) {
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goto LBL_ERR;
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}
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*ret = (mp_cmp_mag(&t, arg) == MP_EQ);
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LBL_ERR:
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mp_clear(&t);
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return err;
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}
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#endif
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