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LibM: Use fptan/fpatan instead of approximating atan2/tan

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The previous versions were very inaccurate, and sometimes wrong.
This commit is contained in:
AnotherTest 2021-04-15 18:42:41 +04:30 committed by Andreas Kling
parent 801daf47f0
commit dbc5b05b7a
Notes: sideshowbarker 2024-07-18 20:18:11 +09:00 
Author: https://github.com/alimpfard
Commit: https://github.com/SerenityOS/serenity/commit/dbc5b05b7a6
Pull-request: https://github.com/SerenityOS/serenity/pull/6347
2 changed files with 24 additions and 7 deletions
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22
Userland/Libraries/LibM/math.cpp
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@ -495,7 +495,7 @@ float tanhf(float x) NOEXCEPT
return (float)tanhl(x);
}
static long double ampsin(long double angle) NOEXCEPT
[[maybe_unused]] static long double ampsin(long double angle) NOEXCEPT
{
long double looped_angle = fmodl(M_PI + angle, M_TAU) - M_PI;
long double looped_angle_squared = looped_angle * looped_angle;
@ -514,7 +514,13 @@ static long double ampsin(long double angle) NOEXCEPT
long double tanl(long double angle) NOEXCEPT
{
return ampsin(angle) / ampsin(M_PI_2 + angle);
long double ret = 0.0, one;
__asm__(
"fptan"
: "=t"(one), "=u"(ret)
: "0"(angle));
return ret;
}
double tan(double angle) NOEXCEPT
@ -721,8 +727,6 @@ float coshf(float x) NOEXCEPT
long double atan2l(long double y, long double x) NOEXCEPT
{
if (x > 0)
return atanl(y / x);
if (x == 0) {
if (y > 0)
return M_PI_2;
@ -730,9 +734,13 @@ long double atan2l(long double y, long double x) NOEXCEPT
return -M_PI_2;
return 0;
}
if (y >= 0)
return atanl(y / x) + M_PI;
return atanl(y / x) - M_PI;
long double result = 0; //atanl(y / x);
__asm__("fpatan"
: "=t"(result)
: "0"(x), "u"(y)
: "st(1)");
return result;
}
double atan2(double y, double x) NOEXCEPT

9
Userland/Tests/LibM/test-math.cpp
View file

@ -29,6 +29,15 @@
#include <float.h>
#include <math.h>
TEST_CASE(atan2)
{
EXPECT_APPROXIMATE(atan2(-1, -0.0e0), -M_PI_2);
EXPECT_APPROXIMATE(atan2(-0.0e0, -1), -M_PI);
EXPECT_APPROXIMATE(atan2(0.0e0, -1), M_PI);
EXPECT_APPROXIMATE(atan2(-0.0e0, 1), -0.0e0);
EXPECT_APPROXIMATE(atan2(0.0e0, 1), 0.0e0);
}
TEST_CASE(trig)
{
EXPECT_APPROXIMATE(sin(1234), 0.601927);