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Add implementation of helpers for uniform float distribution

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Specifically we add
 * `gamma(a, b)`, which returns the magnitude of largest 1-ULP
   step in range [a, b].
 * `count_equidistant_float(a, b, distance)`, which returns the
   number of equi-distant floats in range [a, b].
This commit is contained in:
Martin Hořeňovský
2023-11-19 21:00:53 +01:00
parent bfd9f0f5a6
commit d139b4ff7c
8 changed files with 175 additions and 16 deletions
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59
tests/SelfTest/IntrospectiveTests/FloatingPoint.tests.cpp
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@@ -9,7 +9,9 @@
#include <catch2/catch_test_macros.hpp>
#include <catch2/catch_template_test_macros.hpp>
#include <catch2/internal/catch_floating_point_helpers.hpp>
#include <catch2/internal/catch_random_floating_point_helpers.hpp>
#include <limits>
TEST_CASE("convertToBits", "[floating-point][conversion]") {
using Catch::Detail::convertToBits;
@@ -72,3 +74,60 @@ TEST_CASE("UlpDistance", "[floating-point][ulp][approvals]") {
CHECK( ulpDistance( 1.f, 2.f ) == 0x80'00'00 );
CHECK( ulpDistance( -2.f, 2.f ) == 0x80'00'00'00 );
}
TEMPLATE_TEST_CASE("gamma", "[approvals][floating-point][ulp][gamma]", float, double) {
using Catch::Detail::gamma;
using Catch::Detail::directCompare;
// We need to butcher the equal tests with the directCompare helper,
// because the Wfloat-equal triggers in decomposer rather than here,
// so we cannot locally disable it. Goddamn GCC.
CHECK( directCompare( gamma( TestType( -1. ), TestType( 1. ) ),
gamma( TestType( 0.2332 ), TestType( 1.0 ) ) ) );
CHECK( directCompare( gamma( TestType( -2. ), TestType( 0 ) ),
gamma( TestType( 1. ), TestType( 1.5 ) ) ) );
CHECK( gamma( TestType( 0. ), TestType( 1.0 ) ) <
gamma( TestType( 1.0 ), TestType( 1.5 ) ) );
CHECK( gamma( TestType( 0 ), TestType( 1. ) ) <
std::numeric_limits<TestType>::epsilon() );
CHECK( gamma( TestType( -1. ), TestType( -0. ) ) <
std::numeric_limits<TestType>::epsilon() );
CHECK( directCompare( gamma( TestType( 1. ), TestType( 2. ) ),
std::numeric_limits<TestType>::epsilon() ) );
CHECK( directCompare( gamma( TestType( -2. ), TestType( -1. ) ),
std::numeric_limits<TestType>::epsilon() ) );
}
TEMPLATE_TEST_CASE("count_equidistant_floats",
"[approvals][floating-point][distance]",
float,
double) {
using Catch::Detail::count_equidistant_floats;
auto count_steps = []( TestType a, TestType b ) {
return count_equidistant_floats( a, b, Catch::Detail::gamma( a, b ) );
};
CHECK( count_steps( TestType( -1. ), TestType( 1. ) ) ==
2 * count_steps( TestType( 0. ), TestType( 1. ) ) );
}
TEST_CASE( "count_equidistant_floats",
"[approvals][floating-point][distance]" ) {
using Catch::Detail::count_equidistant_floats;
auto count_floats_with_scaled_ulp = []( auto a, auto b ) {
return count_equidistant_floats( a, b, Catch::Detail::gamma( a, b ) );
};
CHECK( count_floats_with_scaled_ulp( 1., 1.5 ) == 1ull << 51 );
CHECK( count_floats_with_scaled_ulp( 1.25, 1.5 ) == 1ull << 50 );
CHECK( count_floats_with_scaled_ulp( 1.f, 1.5f ) == 1 << 22 );
STATIC_REQUIRE( std::is_same<std::uint64_t,
decltype( count_floats_with_scaled_ulp(
0., 1. ) )>::value );
STATIC_REQUIRE( std::is_same<std::uint32_t,
decltype( count_floats_with_scaled_ulp(
0.f, 1.f ) )>::value );
}