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LibM: Add scalbn and associated functions

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Also implement ldexp in terms of them, and add ldexpl
This commit is contained in:
Mițca Dumitru 2021-03-07 22:23:57 +02:00 • committed by Andreas Kling
parent 8f7aa1e03a
commit 87b61b0eef
3 changed files with 88 additions and 2 deletions
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66
Userland/Libraries/LibM/math.cpp
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@ -1,5 +1,6 @@
/*
* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
* Copyright (c) 2021, Mițca Dumitru <dumitru0mitca@gmail.com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@ -263,6 +264,31 @@ static int internal_ilogb(FloatT x) NOEXCEPT
return (int)extractor.exponent - Extractor::exponent_bias;
}
template<typename FloatT>
static FloatT internal_scalbn(FloatT x, int exponent) NOEXCEPT
{
if (x == 0 || !isfinite(x) || isnan(x) || exponent == 0)
return x;
using Extractor = FloatExtractor<FloatT>;
Extractor extractor;
extractor.d = x;
if (extractor.exponent != 0) {
extractor.exponent = clamp((int)extractor.exponent + exponent, 0, (int)Extractor::exponent_max);
return extractor.d;
}
unsigned leading_mantissa_zeroes = extractor.mantissa == 0 ? 32 : __builtin_clz(extractor.mantissa);
int shift = min((int)leading_mantissa_zeroes, exponent);
exponent = max(exponent - shift, 0);
extractor.exponent <<= shift;
extractor.exponent = exponent + 1;
return extractor.d;
}
extern "C" {
double trunc(double x) NOEXCEPT
@ -333,14 +359,20 @@ float powf(float x, float y) NOEXCEPT
return (float)pow(x, y);
}
// On systems where FLT_RADIX == 2, ldexp is equivalent to scalbn
long double ldexpl(long double x, int exp) NOEXCEPT
{
return internal_scalbn(x, exp);
}
double ldexp(double x, int exp) NOEXCEPT
{
return x * exp2(exp);
return internal_scalbn(x, exp);
}
float ldexpf(float x, int exp) NOEXCEPT
{
return x * exp2f(exp);
return internal_scalbn(x, exp);
}
double tanh(double x) NOEXCEPT
@ -822,4 +854,34 @@ double copysign(double x, double y)
ex.sign = ey.sign;
return ex.d;
}
float scalbnf(float x, int exponent) NOEXCEPT
{
return internal_scalbn(x, exponent);
}
double scalbn(double x, int exponent) NOEXCEPT
{
return internal_scalbn(x, exponent);
}
long double scalbnl(long double x, int exponent) NOEXCEPT
{
return internal_scalbn(x, exponent);
}
float scalbnlf(float x, long exponent) NOEXCEPT
{
return internal_scalbn(x, exponent);
}
double scalbln(double x, long exponent) NOEXCEPT
{
return internal_scalbn(x, exponent);
}
long double scalblnl(long double x, long exponent) NOEXCEPT
{
return internal_scalbn(x, exponent);
}
}

7
Userland/Libraries/LibM/math.h
View file

@ -163,6 +163,13 @@ double nexttoward(double, long double) NOEXCEPT;
float nexttowardf(float, long double) NOEXCEPT;
long double nexttowardl(long double, long double) NOEXCEPT;
float scalbnf(float, int) NOEXCEPT;
double scalbn(double, int) NOEXCEPT;
long double scalbnl(long double, int) NOEXCEPT;
float scalbnlf(float, long) NOEXCEPT;
double scalbln(double, long) NOEXCEPT;
long double scalblnl(long double, long) NOEXCEPT;
double copysign(double x, double y);
__END_DECLS

17
Userland/Tests/LibM/test-math.cpp
View file

@ -26,6 +26,7 @@
#include <AK/TestSuite.h>
#include <float.h>
#include <math.h>
TEST_CASE(trig)
@ -203,4 +204,20 @@ TEST_CASE(nextafter)
EXPECT_EQ(nextafter_translator(Extractor(0x1, 0x419, 0x7d78400000000), Extractor(0x0, 0x0, 0x1)), Extractor(0x1, 0x419, 0x7d783ffffffff));
}
TEST_CASE(scalbn)
{
EXPECT(isnan(scalbn(NAN, 3)));
EXPECT(!isfinite(scalbn(INFINITY, 5)));
EXPECT_EQ(scalbn(0, 3), 0);
EXPECT_EQ(scalbn(15.3, 0), 15.3);
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);
EXPECT(ex.exponent != 0);
EXPECT_EQ(scalbn(2.0, 4), 32.0);
}
TEST_MAIN(Math)