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bignum: introduce bn_one

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This commit is contained in:
Alex Beregszaszi 2016-08-27 13:15:20 +01:00
parent e1dfa81ec5
commit 7e7e462be7
3 changed files with 31 additions and 2 deletions
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18
bignum.c
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@ -204,6 +204,20 @@ void bn_zero(bignum256 *a)
}
}
// sets a bignum to one.
void bn_one(bignum256 *a)
{
a->val[0] = 1;
a->val[1] = 0;
a->val[2] = 0;
a->val[3] = 0;
a->val[4] = 0;
a->val[5] = 0;
a->val[6] = 0;
a->val[7] = 0;
a->val[8] = 0;
}
// checks that a bignum is zero.
// a must be normalized
// function is constant time (on some architectures, in particular ARM).
@ -459,7 +473,7 @@ void bn_sqrt(bignum256 *x, const bignum256 *prime)
// this method compute x^1/2 = x^(prime+1)/4
uint32_t i, j, limb;
bignum256 res, p;
bn_zero(&res); res.val[0] = 1;
bn_one(&res);
// compute p = (prime+1)/4
memcpy(&p, prime, sizeof(bignum256));
bn_addi(&p, 1);
@ -498,7 +512,7 @@ void bn_inverse(bignum256 *x, const bignum256 *prime)
// this method compute x^-1 = x^(prime-2)
uint32_t i, j, limb;
bignum256 res;
bn_zero(&res); res.val[0] = 1;
bn_one(&res);
for (i = 0; i < 9; i++) {
// invariants:
// x = old(x)^(2^(i*30))

2
bignum.h
View File

@ -85,6 +85,8 @@ void bn_zero(bignum256 *a);
int bn_is_zero(const bignum256 *a);
void bn_one(bignum256 *a);
static inline int bn_is_even(const bignum256 *a) {
return (a->val[0] & 1) == 0;
}

13
tests.c
View File

@ -153,6 +153,18 @@ START_TEST(test_bignum_is_zero)
}
END_TEST
START_TEST(test_bignum_one)
{
bignum256 a;
bignum256 b;
bn_read_be(fromhex("0000000000000000000000000000000000000000000000000000000000000001"), &a);
bn_one(&b);
ck_assert_int_eq(bn_is_equal(&a, &b), 1);
}
END_TEST
START_TEST(test_bignum_read_le)
{
bignum256 a;
@ -2602,6 +2614,7 @@ Suite *test_suite(void)
tcase_add_test(tc, test_bignum_is_equal);
tcase_add_test(tc, test_bignum_zero);
tcase_add_test(tc, test_bignum_is_zero);
tcase_add_test(tc, test_bignum_one);
tcase_add_test(tc, test_bignum_read_le);
tcase_add_test(tc, test_bignum_write_le);
tcase_add_test(tc, test_bignum_read_uint32);