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AK: Implement Knuth's algorithm D for dividing UFixedBigInt's

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This commit is contained in:
Dan Klishch 2023-02-04 18:57:10 +03:00 • committed by Andrew Kaster
parent 2470fab05e
commit 2d27c98659
4 changed files with 233 additions and 67 deletions
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57
Tests/AK/TestUFixedBigInt.cpp
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@ -9,6 +9,7 @@
#include <AK/NumericLimits.h>
#include <AK/Random.h>
#include <AK/UFixedBigInt.h>
#include <AK/UFixedBigIntDivision.h>
constexpr int test_iterations = 32;
@ -78,6 +79,62 @@ TEST_CASE(div_mod)
}
}
TEST_CASE(div_anti_knuth)
{
EXPECT_EQ((u256 { { 0ull, 0xffffffffffffffffull, 1ull, 0ull } } / u128 { 0x8000000000000001ull, 0xffffffffffffffffull }), 1u);
EXPECT_EQ((u128 { { 0xffffffff00000000ull, 1ull } } / u128 { 0xffffffff80000001ull }), 1u);
srand(0);
auto generate_u512 = [] {
using namespace AK::Detail;
u512 number;
auto& storage = get_storage_of(number);
static constexpr u32 interesting_words_count = 14;
static constexpr NativeWord interesting_words[interesting_words_count] = {
0,
0,
1,
2,
3,
max_word / 4 - 1,
max_word / 4,
max_word / 2 - 1,
max_word / 2,
max_word / 2 + 1,
max_word / 2 + 2,
max_word - 3,
max_word - 2,
max_word - 1,
};
for (size_t i = 0; i < storage.size(); ++i) {
u32 type = get_random_uniform(interesting_words_count + 1);
NativeWord& next_word = storage[i];
if (type == interesting_words_count)
next_word = get_random<NativeWord>();
else
next_word = interesting_words[type];
}
return number;
};
for (int i = 0; i < 16384; ++i) {
u512 a = generate_u512(), b = generate_u512();
if (b == 0)
continue;
u512 mod;
u512 div = a.div_mod(b, mod);
EXPECT_EQ(div * b + mod, a);
EXPECT_EQ(div.wide_multiply(b) + mod, a);
EXPECT(0 <= mod && mod < b);
}
}
TEST_CASE(shifts)
{
u128 val { 0x1234ULL };