newlib/winsup/mingw/mingwex/math/asinh.c

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#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);
}