1 /* e_acoshf.c -- float version of e_acosh.c.
2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3  */
4 
5 /*
6  * ====================================================
7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8  *
9  * Developed at SunPro, a Sun Microsystems, Inc. business.
10  * Permission to use, copy, modify, and distribute this
11  * software is freely granted, provided that this notice
12  * is preserved.
13  * ====================================================
14  */
15 
16 #include "math.h"
17 #include "math_private.h"
18 
19 static const float
20 one	= 1.0,
21 ln2	= 6.9314718246e-01;  /* 0x3f317218 */
22 
23 float
24 acoshf(float x)
25 {
26 	float t;
27 	int32_t hx;
28 	GET_FLOAT_WORD(hx,x);
29 	if(hx<0x3f800000) {		/* x < 1 */
30 	    return (x-x)/(x-x);
31 	} else if(hx >=0x4d800000) {	/* x > 2**28 */
32 	    if(hx >=0x7f800000) {	/* x is inf of NaN */
33 	        return x+x;
34 	    } else
35 		return logf(x)+ln2;	/* acosh(huge)=log(2x) */
36 	} else if (hx==0x3f800000) {
37 	    return 0.0;			/* acosh(1) = 0 */
38 	} else if (hx > 0x40000000) {	/* 2**28 > x > 2 */
39 	    t=x*x;
40 	    return logf((float)2.0*x-one/(x+sqrtf(t-one)));
41 	} else {			/* 1<x<2 */
42 	    t = x-one;
43 	    return log1pf(t+sqrtf((float)2.0*t+t*t));
44 	}
45 }
46