29 lines
647 B
C
29 lines
647 B
C
|
#include <math.h>
|
||
|
|
#include <errno.h>
|
||
|
|
#include "fastmath.h"
|
||
|
|
|
||
|
|
/* asinh(x) = copysign(log(fabs(x) + sqrt(x * x + 1.0)), x) */
|
||
|
|
double asinh(double x)
|
||
|
|
{
|
||
|
|
double z;
|
||
|
|
if (!isfinite (x))
|
||
|
|
return x;
|
||
|
|
z = fabs (x);
|
||
|
|
|
||
|
|
/* Avoid setting FPU underflow exception flag in x * x. */
|
||
|
|
#if 0
|
||
|
|
if ( z < 0x1p-32)
|
||
|
|
return x;
|
||
|
|
#endif
|
||
|
|
|
||
|
|
/* Use log1p to avoid cancellation with small x. Put
|
||
|
|
x * x in denom, so overflow is harmless.
|
||
|
|
asinh(x) = log1p (x + sqrt (x * x + 1.0) - 1.0)
|
||
|
|
= log1p (x + x * x / (sqrt (x * x + 1.0) + 1.0)) */
|
||
|
|
|
||
|
|
z = __fast_log1p (z + z * z / (__fast_sqrt (z * z + 1.0) + 1.0));
|
||
|
|
|
||
|
|
return ( x > 0.0 ? z : -z);
|
||
|
|
}
|
||
|
|
|