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LibM: Add the gamma family of functions

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Mițca Dumitru 2021-03-14 19:54:01 +02:00 committed by Andreas Kling
parent 7aac174bc8
commit 93c554f6bd
Notes: sideshowbarker 2024-07-18 21:21:39 +09:00 
Author: https://github.com/RealKC
Commit: https://github.com/SerenityOS/serenity/commit/93c554f6bd5
Pull-request: https://github.com/SerenityOS/serenity/pull/5792
2 changed files with 91 additions and 0 deletions
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81
Userland/Libraries/LibM/math.cpp
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@ -312,6 +312,34 @@ static FloatT internal_copysign(FloatT x, FloatT y) NOEXCEPT
return ex.d;
}
template<typename FloatT>
static FloatT internal_gamma(FloatT x) NOEXCEPT
{
if (isnan(x))
return (FloatT)NAN;
if (x < (FloatT)0 && (((long long)x == x) || isinf(x)))
return (FloatT)NAN;
if (isinf(x))
return INFINITY;
using Extractor = FloatExtractor<FloatT>;
if ((long long)x == x) {
// These constants were obtained through use of WolframAlpha, they are (in order): 20!, 18!, 10!
constexpr auto max_factorial_that_fits = (Extractor::mantissa_bits == FloatExtractor<long double>::mantissa_bits ? 2'432'902'008'176'640'000ull : (Extractor::mantissa_bits == FloatExtractor<double>::mantissa_bits ? 6'402'373'705'728'000ull : (Extractor::mantissa_bits == FloatExtractor<float>::mantissa_bits ? 3'628'800ull : 0ull)));
static_assert(max_factorial_that_fits != 0, "internal_gamma needs to be aware of the integer factorial that fits in this floating point type.");
unsigned long long result = 1;
for (; result < max_factorial_that_fits; result++)
result *= result + 1;
return (FloatT)result;
}
// Approximation taken from: <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5840229/>
// Web archive link: <https://web.archive.org/web/20210314174210/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5840229/>
return sqrtl(M_TAU * x) * powl(x / M_E, x) * powl(x * sinhl(1.0l / x), x / 2.0l) * expl((7.0l / 324.0l) * (1.0l / (powl(x, 3.0l) * (35.0l * powl(x, 2.0l) + 33.0l)))) - 1.0l;
}
extern "C" {
float nanf(const char* s) NOEXCEPT
@ -994,6 +1022,59 @@ double gamma(double x) NOEXCEPT
return sqrt(2.0 * M_PI / x) * pow(x / M_E, x);
}
long double tgammal(long double value) NOEXCEPT
{
return internal_gamma(value);
}
double tgamma(double value) NOEXCEPT
{
return internal_gamma(value);
}
float tgammaf(float value) NOEXCEPT
{
return internal_gamma(value);
}
int signgam = 0;
long double lgammal(long double value) NOEXCEPT
{
return lgammal_r(value, &signgam);
}
double lgamma(double value) NOEXCEPT
{
return lgamma_r(value, &signgam);
}
float lgammaf(float value) NOEXCEPT
{
return lgammaf_r(value, &signgam);
}
long double lgammal_r(long double value, int* sign) NOEXCEPT
{
long double result = logl(internal_gamma(value));
*sign = signbit(result);
return result;
}
double lgamma_r(double value, int* sign) NOEXCEPT
{
double result = log(internal_gamma(value));
*sign = signbit(result);
return result;
}
float lgammaf_r(float value, int* sign) NOEXCEPT
{
float result = logf(internal_gamma(value));
*sign = signbit(result);
return result;
}
long double expm1l(long double x) NOEXCEPT
{
return expl(x) - 1;

10
Userland/Libraries/LibM/math.h
View File

@ -179,6 +179,16 @@ long double erfcl(long double) NOEXCEPT;
double erfc(double) NOEXCEPT;
float erfcf(float) NOEXCEPT;
double gamma(double) NOEXCEPT;
long double tgammal(long double) NOEXCEPT;
double tgamma(double) NOEXCEPT;
float tgammaf(float) NOEXCEPT;
long double lgammal(long double) NOEXCEPT;
double lgamma(double) NOEXCEPT;
float lgammaf(float) NOEXCEPT;
long double lgammal_r(long double, int*) NOEXCEPT;
double lgamma_r(double, int*) NOEXCEPT;
float lgammaf_r(float, int*) NOEXCEPT;
extern int signgam;
/* Nearest integer floating point operations */
long double ceill(long double) NOEXCEPT;