1/* s_log1pf.c -- float version of s_log1p.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 <sys/cdefs.h>
17#if defined(LIBM_SCCS) && !defined(lint)
18__RCSID("$NetBSD: s_log1pf.c,v 1.9 2024/07/16 14:52:50 riastradh Exp $");
19#endif
20
21#include "namespace.h"
22
23#include "math.h"
24#include "math_private.h"
25
26static const float
27ln2_hi =   6.9313812256e-01,	/* 0x3f317180 */
28ln2_lo =   9.0580006145e-06,	/* 0x3717f7d1 */
29two25 =    3.355443200e+07,	/* 0x4c000000 */
30Lp1 = 6.6666668653e-01,	/* 3F2AAAAB */
31Lp2 = 4.0000000596e-01,	/* 3ECCCCCD */
32Lp3 = 2.8571429849e-01, /* 3E924925 */
33Lp4 = 2.2222198546e-01, /* 3E638E29 */
34Lp5 = 1.8183572590e-01, /* 3E3A3325 */
35Lp6 = 1.5313838422e-01, /* 3E1CD04F */
36Lp7 = 1.4798198640e-01; /* 3E178897 */
37
38static const float zero = 0.0;
39
40__weak_alias(log1pf, _log1pf)
41float
42log1pf(float x)
43{
44	float hfsq,f,c,s,z,R,u;
45	int32_t k,hx,hu,ax;
46
47	f = c = 0;
48	hu = 0;
49	GET_FLOAT_WORD(hx,x);
50	ax = hx&0x7fffffff;
51
52	k = 1;
53	if (hx < 0x3ed413d7) {			/* x < 0.41422  */
54	    if(ax>=0x3f800000) {		/* x <= -1.0 */
55		if(x==(float)-1.0) return -two25/zero; /* log1p(-1)=+inf */
56		else return (x-x)/(x-x);	/* log1p(x<-1)=NaN */
57	    }
58	    if(ax<0x31000000) {			/* |x| < 2**-29 */
59		if(two25+x>zero			/* raise inexact */
60	            &&ax<0x24800000) 		/* |x| < 2**-54 */
61		    return x;
62		else
63		    return x - x*x*(float)0.5;
64	    }
65	    if(hx>0||hx<=((int32_t)0xbe95f61f)) {
66		k=0;f=x;hu=1;}	/* -0.2929<x<0.41422 */
67	}
68	if (hx >= 0x7f800000) return x+x;
69	if(k!=0) {
70	    if(hx<0x5a000000) {
71		u  = (float)1.0+x;
72		GET_FLOAT_WORD(hu,u);
73	        k  = (hu>>23)-127;
74		/* correction term */
75	        c  = (k>0)? (float)1.0-(u-x):x-(u-(float)1.0);
76		c /= u;
77	    } else {
78		u  = x;
79		GET_FLOAT_WORD(hu,u);
80	        k  = (hu>>23)-127;
81		c  = 0;
82	    }
83	    hu &= 0x007fffff;
84	    if(hu<0x3504f7) {
85	        SET_FLOAT_WORD(u,hu|0x3f800000);/* normalize u */
86	    } else {
87	        k += 1;
88		SET_FLOAT_WORD(u,hu|0x3f000000);	/* normalize u/2 */
89	        hu = (0x00800000-hu)>>2;
90	    }
91	    f = u-(float)1.0;
92	}
93	hfsq=(float)0.5*f*f;
94	if(hu==0) {	/* |f| < 2**-20 */
95	    if(f==zero) { if(k==0) return zero;
96			  else {c += k*ln2_lo; return k*ln2_hi+c;}
97	    }
98	    R = hfsq*((float)1.0-(float)0.66666666666666666*f);
99	    if(k==0) return f-R; else
100	    	     return k*ln2_hi-((R-(k*ln2_lo+c))-f);
101	}
102 	s = f/((float)2.0+f);
103	z = s*s;
104	R = z*(Lp1+z*(Lp2+z*(Lp3+z*(Lp4+z*(Lp5+z*(Lp6+z*Lp7))))));
105	if(k==0) return f-(hfsq-s*(hfsq+R)); else
106		 return k*ln2_hi-((hfsq-(s*(hfsq+R)+(k*ln2_lo+c)))-f);
107}
108