mirror of
https://gitea.nishi.boats/pyrite-dev/milsko
synced 2025-12-31 06:30:52 +00:00
7f523a3d76
git-svn-id: http://svn2.nishi.boats/svn/milsko/trunk@557 b9cfdab3-6d41-4d17-bbe4-086880011989
54 lines
1.5 KiB
C
54 lines
1.5 KiB
C
|
|
/* @(#)s_asinh.c 1.3 95/01/18 */
|
|
/*
|
|
* ====================================================
|
|
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
|
|
*
|
|
* Developed at SunSoft, a Sun Microsystems, Inc. business.
|
|
* Permission to use, copy, modify, and distribute this
|
|
* software is freely granted, provided that this notice
|
|
* is preserved.
|
|
* ====================================================
|
|
*/
|
|
|
|
/* asinh(x)
|
|
* Method :
|
|
* Based on
|
|
* asinh(x) = sign(x) * log [ |x| + sqrt(x*x+1) ]
|
|
* we have
|
|
* asinh(x) := x if 1+x*x=1,
|
|
* := sign(x)*(log(x)+ln2)) for large |x|, else
|
|
* := sign(x)*log(2|x|+1/(|x|+sqrt(x*x+1))) if|x|>2, else
|
|
* := sign(x)*log1p(|x| + x^2/(1 + sqrt(1+x^2)))
|
|
*/
|
|
|
|
#include "math.h"
|
|
|
|
static const double
|
|
one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
|
|
ln2 = 6.93147180559945286227e-01, /* 0x3FE62E42, 0xFEFA39EF */
|
|
hugev = 1.00000000000000000000e+300;
|
|
|
|
double asinh(double x) {
|
|
double t, w;
|
|
int hx, ix;
|
|
hx = __HI(x);
|
|
ix = hx & 0x7fffffff;
|
|
if(ix >= 0x7ff00000) return x + x; /* x is inf or NaN */
|
|
if(ix < 0x3e300000) { /* |x|<2**-28 */
|
|
if(hugev + x > one) return x; /* return x inexact except 0 */
|
|
}
|
|
if(ix > 0x41b00000) { /* |x| > 2**28 */
|
|
w = __fdlibm_log(fabs(x)) + ln2;
|
|
} else if(ix > 0x40000000) { /* 2**28 > |x| > 2.0 */
|
|
t = fabs(x);
|
|
w = __fdlibm_log(2.0 * t + one / (sqrt(x * x + one) + t));
|
|
} else { /* 2.0 > |x| > 2**-28 */
|
|
t = x * x;
|
|
w = log1p(fabs(x) + t / (one + sqrt(one + t)));
|
|
}
|
|
if(hx > 0) return w;
|
|
else
|
|
return -w;
|
|
}
|