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AK: Replace FP math in is_power_of with a purely integral algorithm

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The previous naive approach was causing test failures because of
rounding issues in some exotic environments. In particular, MSVC
via MSBuild
This commit is contained in:
Abuneri 2024-05-04 19:48:07 -07:00 • committed by Andrew Kaster
commit b5bed37074
Notes: sideshowbarker 2024-07-17 06:39:26 +09:00
2 changed files with 25 additions and 8 deletions
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14
Tests/AK/TestIntegerMath.cpp
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@ -11,6 +11,7 @@
TEST_CASE(pow)
{
EXPECT_EQ(AK::pow<u64>(0, 0), 1ull);
EXPECT_EQ(AK::pow<u64>(10, 0), 1ull);
EXPECT_EQ(AK::pow<u64>(10, 1), 10ull);
EXPECT_EQ(AK::pow<u64>(10, 2), 100ull);
@ -22,12 +23,21 @@ TEST_CASE(pow)
TEST_CASE(is_power_of)
{
constexpr auto check_prime = []<u64 prime>(u64 limit) {
for (u64 power = 0; power < limit; ++power)
EXPECT(!AK::is_power_of<0>(10ull));
// We don't have enough context to know if the input was from 0^0
EXPECT(!AK::is_power_of<0>(1ull));
EXPECT(!AK::is_power_of<1>(10ull));
EXPECT(!AK::is_power_of<1>(0ull));
constexpr auto check_prime = []<u64 prime>(u64 limit, u64 init = 0) {
for (u64 power = init; power < limit; ++power)
EXPECT(AK::is_power_of<prime>(AK::pow(prime, power)));
};
// Limits calculated as floor( log_{prime}(2^64) ) to prevent overflows.
check_prime.operator()<0>(42, 1);
check_prime.operator()<1>(36);
check_prime.operator()<2>(64);
check_prime.operator()<3>(40);
check_prime.operator()<5>(27);