RGBCube/serenity
1
Fork 0
mirror of https://github.com/RGBCube/serenity synced 2025-07-25 06:37:43 +00:00
Code Issues Activity Actions

LibM: Implement nextafter() and nexttoward()

Browse source 
Patch from Anonymous.
This commit is contained in:
Andreas Kling 2021-02-05 12:27:00 +01:00
parent e87eac9273
commit 0269578d3e
2 changed files with 186 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

99
Userland/Libraries/LibM/math.cpp
View file

@ -70,11 +70,14 @@ union FloatExtractor;
template<>
union FloatExtractor<double> {
static const int mantissa_bits = 52;
static const unsigned long long mantissa_max = (1ull << 52) - 1;
static const int exponent_bias = 1023;
static const int exponent_bits = 11;
static const unsigned exponent_max = 2047;
struct {
unsigned long long mantissa : 52;
unsigned exponent : 11;
int sign : 1;
unsigned sign : 1;
};
double d;
};
@ -82,11 +85,14 @@ union FloatExtractor<double> {
template<>
union FloatExtractor<float> {
static const int mantissa_bits = 23;
static const unsigned mantissa_max = (1 << 23) - 1;
static const int exponent_bias = 127;
static const int exponent_bits = 8;
static const unsigned exponent_max = 255;
struct {
unsigned long long mantissa : 23;
unsigned exponent : 8;
int sign : 1;
unsigned sign : 1;
};
float d;
};
@ -152,6 +158,71 @@ static FloatType internal_to_integer(FloatType x, RoundingMode rounding_mode)
return extractor.d;
}
// This is much branchier than it really needs to be
template<typename FloatType>
static FloatType internal_nextafter(FloatType x, bool up)
{
if (!isfinite(x))
return x;
using Extractor = FloatExtractor<decltype(x)>;
Extractor extractor;
extractor.d = x;
if (x == 0) {
if (!extractor.sign) {
extractor.mantissa = 1;
extractor.sign = !up;
return extractor.d;
}
if (up) {
extractor.sign = false;
extractor.mantissa = 1;
return extractor.d;
}
extractor.mantissa = 1;
extractor.sign = up != extractor.sign;
return extractor.d;
}
if (up != extractor.sign) {
extractor.mantissa++;
if (!extractor.mantissa) {
// no need to normalize the mantissa as we just hit a power
// of two.
extractor.exponent++;
if (extractor.exponent == Extractor::exponent_max) {
extractor.exponent = Extractor::exponent_max - 1;
extractor.mantissa = Extractor::mantissa_max;
}
}
return extractor.d;
}
if (!extractor.mantissa) {
if (extractor.exponent) {
extractor.exponent--;
extractor.mantissa = Extractor::mantissa_max;
} else {
extractor.d = 0;
}
return extractor.d;
}
extractor.mantissa--;
if (extractor.mantissa != Extractor::mantissa_max)
return extractor.d;
if (extractor.exponent) {
extractor.exponent--;
// normalize
extractor.mantissa <<= 1;
} else {
if (extractor.sign) {
// Negative infinity
extractor.mantissa = 0;
extractor.exponent = Extractor::exponent_max;
}
}
return extractor.d;
}
extern "C" {
double trunc(double x) NOEXCEPT
@ -634,14 +705,18 @@ double erfc(double x) NOEXCEPT
return 1 - erf(x);
}
double nextafter(double, double) NOEXCEPT
double nextafter(double x, double target) NOEXCEPT
{
TODO();
if (x == target)
return target;
return internal_nextafter(x, target >= x);
}
float nextafterf(float, float) NOEXCEPT
float nextafterf(float x, float target) NOEXCEPT
{
TODO();
if (x == target)
return target;
return internal_nextafter(x, target >= x);
}
long double nextafterl(long double, long double) NOEXCEPT
@ -649,14 +724,18 @@ long double nextafterl(long double, long double) NOEXCEPT
TODO();
}
double nexttoward(double, long double) NOEXCEPT
double nexttoward(double x, long double target) NOEXCEPT
{
TODO();
if (x == target)
return target;
return internal_nextafter(x, target >= x);
}
float nexttowardf(float, long double) NOEXCEPT
float nexttowardf(float x, long double target) NOEXCEPT
{
TODO();
if (x == target)
return target;
return internal_nextafter(x, target >= x);
}
long double nexttowardl(long double, long double) NOEXCEPT