56 lines
1.6 KiB
C
56 lines
1.6 KiB
C
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/*
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* Copyright Supranational LLC
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* Licensed under the Apache License, Version 2.0, see LICENSE for details.
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include "vect.h"
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/*
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* |out| = |inp|^|pow|, small footprint, public exponent
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*/
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static void exp_mont_384(vec384 out, const vec384 inp, const byte *pow,
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size_t pow_bits, const vec384 p, limb_t n0)
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{
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#if 1
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vec384 ret;
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vec_copy(ret, inp, sizeof(ret)); /* ret = inp^1 */
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--pow_bits; /* most significant bit is set, skip over */
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while (pow_bits--) {
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sqr_mont_384(ret, ret, p, n0);
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if (is_bit_set(pow, pow_bits))
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mul_mont_384(ret, ret, inp, p, n0);
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}
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vec_copy(out, ret, sizeof(ret)); /* out = ret */
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#else
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unsigned int i;
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vec384 sqr;
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vec_copy(sqr, inp, sizeof(sqr));
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for (i = 0; !is_bit_set(pow, i++);)
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sqr_mont_384(sqr, sqr, sqr, p, n0);
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vec_copy(out, sqr, sizeof(sqr));
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for (; i < pow_bits; i++) {
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sqr_mont_384(sqr, sqr, sqr, p, n0);
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if (is_bit_set(pow, i))
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mul_mont_384(out, out, sqr, p, n0);
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}
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#endif
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}
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static void exp_mont_384x(vec384x out, const vec384x inp, const byte *pow,
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size_t pow_bits, const vec384 p, limb_t n0)
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{
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vec384x ret;
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vec_copy(ret, inp, sizeof(ret)); /* |ret| = |inp|^1 */
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--pow_bits; /* most significant bit is accounted for, skip over */
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while (pow_bits--) {
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sqr_mont_384x(ret, ret, p, n0);
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if (is_bit_set(pow, pow_bits))
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mul_mont_384x(ret, ret, inp, p, n0);
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}
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vec_copy(out, ret, sizeof(ret)); /* |out| = |ret| */
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}
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