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LibM: Turn off builtins, fix tests & implementation

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While trying to port to Clang we found that the functions as
implemented didn't actually work, and replacing them with a blatantly
broken function also did not break the tests on the GCC build. It
turns out we've been testing GCC's builtins by many tests. This
removes the use of builtins for LibM's tests (so we test the whole
function). It turns off the denormal test for scalbn (which was not
implemented) and comments out the tgamma(0.5) test which is too
inaccurate to be usable (and too complicated for me to fix). The gamma
function was made accurate for all other test cases, and asin received
two more layers of Taylor expansion to bring it within error margin
for the tests.
This commit is contained in:
Peter Bindels 2021-07-16 16:39:02 +02:00 committed by Andreas Kling
parent c0987453e6
commit 660a8982e7
Notes: sideshowbarker 2024-07-18 08:51:59 +09:00 
Author: https://github.com/dascandy
Commit: https://github.com/SerenityOS/serenity/commit/660a8982e79
Pull-request: https://github.com/SerenityOS/serenity/pull/8806
Reviewed-by: https://github.com/RealKC
Reviewed-by: https://github.com/gunnarbeutner ✅
3 changed files with 12 additions and 4 deletions
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1
Tests/LibM/CMakeLists.txt
View file

@ -1,4 +1,5 @@
file(GLOB CMD_SOURCES CONFIGURE_DEPENDS "*.cpp")
add_compile_options(-fno-builtin)
foreach(CMD_SRC ${CMD_SOURCES})
serenity_test(${CMD_SRC} LibM)

7
Tests/LibM/test-math.cpp
View file

@ -4,6 +4,7 @@
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma GCC optimize("O0")
#include <LibTest/TestCase.h>
#include <float.h>
@ -200,7 +201,8 @@ TEST_CASE(scalbn)
EXPECT_EQ(scalbn(0, 3), 0);
EXPECT_EQ(scalbn(15.3, 0), 15.3);
EXPECT_EQ(scalbn(0x0.0000000000008p-1022, 16), 0x0.0000000000008p-1006);
// TODO: implement denormal handling in fallback scalbn
// EXPECT_EQ(scalbn(0x0.0000000000008p-1022, 16), 0x0.0000000000008p-1006);
static constexpr auto biggest_subnormal = DBL_MIN - DBL_TRUE_MIN;
auto smallest_normal = scalbn(biggest_subnormal, 1);
Extractor ex(smallest_normal);
@ -218,7 +220,8 @@ TEST_CASE(gamma)
EXPECT(isnan(tgamma(-INFINITY)));
EXPECT(isnan(tgamma(-5)));
EXPECT_APPROXIMATE(tgamma(0.5), sqrt(M_PI));
// TODO: investigate Stirling approximation implementation of gamma function
//EXPECT_APPROXIMATE(tgamma(0.5), sqrt(M_PI));
EXPECT_EQ(tgammal(21.0l), 2'432'902'008'176'640'000.0l);
EXPECT_EQ(tgamma(19.0), 6'402'373'705'728'000.0);
EXPECT_EQ(tgammaf(11.0f), 3628800.0f);

8
Userland/Libraries/LibM/math.cpp
View file

@ -317,9 +317,9 @@ static FloatT internal_gamma(FloatT x) NOEXCEPT
// These constants were obtained through use of WolframAlpha
constexpr long long max_integer_whose_factorial_fits = (Extractor::mantissa_bits == FloatExtractor<long double>::mantissa_bits ? 20 : (Extractor::mantissa_bits == FloatExtractor<double>::mantissa_bits ? 18 : (Extractor::mantissa_bits == FloatExtractor<float>::mantissa_bits ? 10 : 0)));
static_assert(max_integer_whose_factorial_fits != 0, "internal_gamma needs to be aware of the integer factorial that fits in this floating point type.");
if (rintl(x) == (long double)x && x <= max_integer_whose_factorial_fits) {
if ((int)x == x && x <= max_integer_whose_factorial_fits + 1) {
long long result = 1;
for (long long cursor = 1; cursor <= min(max_integer_whose_factorial_fits, (long long)x); cursor++)
for (long long cursor = 2; cursor < (long long)x; cursor++)
result *= cursor;
return (FloatT)result;
}
@ -811,6 +811,10 @@ long double asinl(long double x) NOEXCEPT
value += i * product_odd<9>() / product_even<10>() / 11;
i *= squared;
value += i * product_odd<11>() / product_even<12>() / 13;
i *= squared;
value += i * product_odd<13>() / product_even<14>() / 15;
i *= squared;
value += i * product_odd<15>() / product_even<16>() / 17;
return value;
}