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/***********************************************************************
* Copyright (c) 2013, 2014, 2015 Pieter Wuille, Gregory Maxwell *
* Distributed under the MIT software license, see the accompanying *
* file COPYING or https://www.opensource.org/licenses/mit-license.php.*
***********************************************************************/
#ifndef SECP256K1_ECMULT_GEN_COMPUTE_TABLE_IMPL_H
#define SECP256K1_ECMULT_GEN_COMPUTE_TABLE_IMPL_H
#include "ecmult_gen_compute_table.h"
#include "group_impl.h"
#include "field_impl.h"
#include "ecmult_gen.h"
#include "util.h"
static void secp256k1_ecmult_gen_compute_table(secp256k1_ge_storage* table, const secp256k1_ge* gen, int bits) {
int g = ECMULT_GEN_PREC_G(bits);
int n = ECMULT_GEN_PREC_N(bits);
secp256k1_ge* prec = checked_malloc(&default_error_callback, n * g * sizeof(*prec));
secp256k1_gej gj;
secp256k1_gej nums_gej;
int i, j;
VERIFY_CHECK(g > 0);
VERIFY_CHECK(n > 0);
/* get the generator */
secp256k1_gej_set_ge(&gj, gen);
/* Construct a group element with no known corresponding scalar (nothing up my sleeve). */
{
static const unsigned char nums_b32[33] = "The scalar for this x is unknown";
secp256k1_fe nums_x;
secp256k1_ge nums_ge;
int r;
r = secp256k1_fe_set_b32_limit(&nums_x, nums_b32);
(void)r;
VERIFY_CHECK(r);
r = secp256k1_ge_set_xo_var(&nums_ge, &nums_x, 0);
(void)r;
VERIFY_CHECK(r);
secp256k1_gej_set_ge(&nums_gej, &nums_ge);
/* Add G to make the bits in x uniformly distributed. */
secp256k1_gej_add_ge_var(&nums_gej, &nums_gej, gen, NULL);
}
/* compute prec. */
{
secp256k1_gej gbase;
secp256k1_gej numsbase;
secp256k1_gej* precj = checked_malloc(&default_error_callback, n * g * sizeof(*precj)); /* Jacobian versions of prec. */
gbase = gj; /* PREC_G^j * G */
numsbase = nums_gej; /* 2^j * nums. */
for (j = 0; j < n; j++) {
/* Set precj[j*PREC_G .. j*PREC_G+(PREC_G-1)] to (numsbase, numsbase + gbase, ..., numsbase + (PREC_G-1)*gbase). */
precj[j*g] = numsbase;
for (i = 1; i < g; i++) {
secp256k1_gej_add_var(&precj[j*g + i], &precj[j*g + i - 1], &gbase, NULL);
}
/* Multiply gbase by PREC_G. */
for (i = 0; i < bits; i++) {
secp256k1_gej_double_var(&gbase, &gbase, NULL);
}
/* Multiply numbase by 2. */
secp256k1_gej_double_var(&numsbase, &numsbase, NULL);
if (j == n - 2) {
/* In the last iteration, numsbase is (1 - 2^j) * nums instead. */
secp256k1_gej_neg(&numsbase, &numsbase);
secp256k1_gej_add_var(&numsbase, &numsbase, &nums_gej, NULL);
}
}
secp256k1_ge_set_all_gej_var(prec, precj, n * g);
free(precj);
}
for (j = 0; j < n; j++) {
for (i = 0; i < g; i++) {
secp256k1_ge_to_storage(&table[j*g + i], &prec[j*g + i]);
}
}
free(prec);
}
#endif /* SECP256K1_ECMULT_GEN_COMPUTE_TABLE_IMPL_H */
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