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bignum: implement bitcount

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This commit is contained in:
Alex Beregszaszi 2016-08-26 12:31:51 +01:00
parent 29e82018cd
commit 7956c2f2f1
3 changed files with 34 additions and 0 deletions
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13
bignum.c
View File

@ -182,6 +182,19 @@ void bn_read_uint64(uint64_t in_number, bignum256 *out_number)
out_number->val[8] = 0;
}
// a must be normalized
int bn_bitcount(const bignum256 *a)
{
int i;
for (i = 8; i >= 0; i--) {
int tmp = a->val[i];
if (tmp != 0) {
return i * 30 + (32 - __builtin_clz(tmp));
}
}
return 0;
}
// sets a bignum to zero.
void bn_zero(bignum256 *a)
{

2
bignum.h
View File

@ -63,6 +63,8 @@ static inline void bn_copy(const bignum256 *a, bignum256 *b) {
*b = *a;
}
int bn_bitcount(const bignum256 *a);
void bn_zero(bignum256 *a);
int bn_is_zero(const bignum256 *a);

19
tests.c
View File

@ -275,6 +275,24 @@ START_TEST(test_bignum_is_odd)
}
END_TEST
START_TEST(test_bignum_bitcount)
{
bignum256 a;
bn_zero(&a);
ck_assert_int_eq(bn_bitcount(&a), 0);
bn_read_uint32(0x3fffffff, &a);
ck_assert_int_eq(bn_bitcount(&a), 30);
bn_read_uint32(0xffffffff, &a);
ck_assert_int_eq(bn_bitcount(&a), 32);
bn_read_be(fromhex("ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"), &a);
ck_assert_int_eq(bn_bitcount(&a), 256);
}
END_TEST
// from https://github.com/bitcoin/bitcoin/blob/master/src/test/data/base58_keys_valid.json
START_TEST(test_base58)
{
@ -2532,6 +2550,7 @@ Suite *test_suite(void)
tcase_add_test(tc, test_bignum_copy);
tcase_add_test(tc, test_bignum_is_even);
tcase_add_test(tc, test_bignum_is_odd);
tcase_add_test(tc, test_bignum_bitcount);
suite_add_tcase(s, tc);
tc = tcase_create("base58");