secp256k1-zkp/src/testrand_impl.h

/**********************************************************************
 * Copyright (c) 2013-2015 Pieter Wuille                              *
 * Distributed under the MIT software license, see the accompanying   *
 * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
 **********************************************************************/

#ifndef _SECP256K1_TESTRAND_IMPL_H_
#define _SECP256K1_TESTRAND_IMPL_H_

#include <stdint.h>
#include <string.h>

#include "testrand.h"
#include "hash.h"

static secp256k1_rfc6979_hmac_sha256_t secp256k1_test_rng;
static uint32_t secp256k1_test_rng_precomputed[8];
static int secp256k1_test_rng_precomputed_used = 8;
static uint64_t secp256k1_test_rng_integer;
static int secp256k1_test_rng_integer_bits_left = 0;

SECP256K1_INLINE static void secp256k1_rand_seed(const unsigned char *seed16) {
    secp256k1_rfc6979_hmac_sha256_initialize(&secp256k1_test_rng, seed16, 16);
}

SECP256K1_INLINE static uint32_t secp256k1_rand32(void) {
    if (secp256k1_test_rng_precomputed_used == 8) {
        secp256k1_rfc6979_hmac_sha256_generate(&secp256k1_test_rng, (unsigned char*)(&secp256k1_test_rng_precomputed[0]), sizeof(secp256k1_test_rng_precomputed));
        secp256k1_test_rng_precomputed_used = 0;
    }
    return secp256k1_test_rng_precomputed[secp256k1_test_rng_precomputed_used++];
}

static uint32_t secp256k1_rand_bits(int bits) {
    uint32_t ret;
    if (secp256k1_test_rng_integer_bits_left < bits) {
        secp256k1_test_rng_integer |= (((uint64_t)secp256k1_rand32()) << secp256k1_test_rng_integer_bits_left);
        secp256k1_test_rng_integer_bits_left += 32;
    }
    ret = secp256k1_test_rng_integer;
    secp256k1_test_rng_integer >>= bits;
    secp256k1_test_rng_integer_bits_left -= bits;
    ret &= ((~((uint32_t)0)) >> (32 - bits));
    return ret;
}

static uint32_t secp256k1_rand_int(uint32_t range) {
    int bits = 0;
    uint32_t ret = range - 1;
    if (range <= 1) {
        return 0;
    }
    while (ret > 0) {
        ret >>= 1;
        bits++;
    }
    while (1) {
        ret = secp256k1_rand_bits(bits);
        if (ret < range) {
            return ret;
        }
    }
}

static void secp256k1_rand256(unsigned char *b32) {
    secp256k1_rfc6979_hmac_sha256_generate(&secp256k1_test_rng, b32, 32);
}

static void secp256k1_rand_bytes_test(unsigned char *bytes, size_t len) {
    size_t bits = 0;
    memset(bytes, 0, len);
    while (bits < len * 8) {
        int now;
        uint32_t val;
        now = 1 + (secp256k1_rand_bits(6) * secp256k1_rand_bits(5) + 16) / 31;
        val = secp256k1_rand_bits(1);
        while (now > 0 && bits < len * 8) {
            bytes[bits / 8] |= val << (bits % 8);
            now--;
            bits++;
        }
    }
}

static void secp256k1_rand256_test(unsigned char *b32) {
    secp256k1_rand_bytes_test(b32, 32);
}

#endif