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bignum: introduce read/write_le

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This commit is contained in:
Alex Beregszaszi 2016-08-25 23:18:24 +01:00
parent ec316b6afc
commit 62a0db8c4e
4 changed files with 95 additions and 0 deletions
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1
CONTRIBUTORS
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@ -4,6 +4,7 @@ Jochen Hoenicke <hoenicke@gmail.com>
Dustin Laurence <dustin@laurences.net>
Ondrej Mikle <ondrej.mikle@nic.cz>
Roman Zeyde <roman.zeyde@gmail.com>
Alex Beregszaszi <alex@rtfs.hu>
netanelkl <netanel.keidar@gmail.com>
Jan Pochyla <jpochyla@gmail.com>
Ondrej Mikle <ondrej.mikle@gmail.com>

52
bignum.c
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@ -2,6 +2,7 @@
* Copyright (c) 2013-2014 Tomas Dzetkulic
* Copyright (c) 2013-2014 Pavol Rusnak
* Copyright (c) 2015 Jochen Hoenicke
* Copyright (c) 2016 Alex Beregszaszi
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the "Software"),
@ -69,6 +70,22 @@ inline void write_be(uint8_t *data, uint32_t x)
data[3] = x;
}
inline uint32_t read_le(const uint8_t *data)
{
return (((uint32_t)data[3]) << 24) |
(((uint32_t)data[2]) << 16) |
(((uint32_t)data[1]) << 8) |
(((uint32_t)data[0]));
}
inline void write_le(uint8_t *data, uint32_t x)
{
data[3] = x >> 24;
data[2] = x >> 16;
data[1] = x >> 8;
data[0] = x;
}
// convert a raw bigendian 256 bit value into a normalized bignum.
// out_number is partly reduced (since it fits in 256 bit).
void bn_read_be(const uint8_t *in_number, bignum256 *out_number)
@ -104,6 +121,41 @@ void bn_write_be(const bignum256 *in_number, uint8_t *out_number)
}
}
// convert a raw little endian 256 bit value into a normalized bignum.
// out_number is partly reduced (since it fits in 256 bit).
void bn_read_le(const uint8_t *in_number, bignum256 *out_number)
{
int i;
uint32_t temp = 0;
for (i = 0; i < 8; i++) {
// invariant: temp = (in_number % 2^(32i)) >> 30i
// get next limb = (in_number % 2^(32(i+1))) >> 32i
uint32_t limb = read_le(in_number + i * 4);
// temp = (in_number % 2^(32(i+1))) << 30i
temp |= limb << (2*i);
// store 30 bits into val[i]
out_number->val[i]= temp & 0x3FFFFFFF;
// prepare temp for next round
temp = limb >> (30 - 2*i);
}
out_number->val[8] = temp;
}
// convert a normalized bignum to a raw little endian 256 bit number.
// in_number must be fully reduced.
void bn_write_le(const bignum256 *in_number, uint8_t *out_number)
{
int i;
uint32_t temp = in_number->val[8] << 16;
for (i = 0; i < 8; i++) {
// invariant: temp = (in_number >> 30*(8-i)) << (16 + 2i)
uint32_t limb = in_number->val[7 - i];
temp |= limb >> (14 - 2*i);
write_le(out_number + (7 - i) * 4, temp);
temp = limb << (18 + 2*i);
}
}
// sets a bignum to zero.
void bn_zero(bignum256 *a)
{

10
bignum.h
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@ -39,10 +39,20 @@ uint32_t read_be(const uint8_t *data);
// write 4 big endian bytes
void write_be(uint8_t *data, uint32_t x);
// read 4 little endian bytes into uint32
uint32_t read_le(const uint8_t *data);
// write 4 little endian bytes
void write_le(uint8_t *data, uint32_t x);
void bn_read_be(const uint8_t *in_number, bignum256 *out_number);
void bn_write_be(const bignum256 *in_number, uint8_t *out_number);
void bn_read_le(const uint8_t *in_number, bignum256 *out_number);
void bn_write_le(const bignum256 *in_number, uint8_t *out_number);
void bn_zero(bignum256 *a);
int bn_is_zero(const bignum256 *a);

32
tests.c
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@ -123,6 +123,36 @@ START_TEST(test_bignum_equal)
}
END_TEST
START_TEST(test_bignum_read_le)
{
bignum256 a;
bignum256 b;
bn_read_be(fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd5"), &a);
bn_read_le(fromhex("d58b6de8051f031eeca2c6d7fbe1b5d37c4314fe1068f96352dd0d8b85ce5ec5"), &b);
ck_assert_int_eq(bn_is_equal(&a, &b), 1);
}
END_TEST
START_TEST(test_bignum_write_le)
{
bignum256 a;
bignum256 b;
uint8_t tmp[32];
bn_read_be(fromhex("c55ece858b0ddd5263f96810fe14437cd3b5e1fbd7c6a2ec1e031f05e86d8bd5"), &a);
bn_write_le(&a, tmp);
bn_read_le(tmp, &b);
ck_assert_int_eq(bn_is_equal(&a, &b), 1);
bn_read_be(fromhex("d58b6de8051f031eeca2c6d7fbe1b5d37c4314fe1068f96352dd0d8b85ce5ec5"), &a);
bn_read_be(tmp, &b);
ck_assert_int_eq(bn_is_equal(&a, &b), 1);
}
END_TEST
// from https://github.com/bitcoin/bitcoin/blob/master/src/test/data/base58_keys_valid.json
START_TEST(test_base58)
{
@ -2371,6 +2401,8 @@ Suite *test_suite(void)
tcase_add_test(tc, test_bignum_read_be);
tcase_add_test(tc, test_bignum_write_be);
tcase_add_test(tc, test_bignum_equal);
tcase_add_test(tc, test_bignum_read_le);
tcase_add_test(tc, test_bignum_write_le);
suite_add_tcase(s, tc);
tc = tcase_create("base58");