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 __FBSDID("$FreeBSD$");
18
19 #include <float.h>
20
21 #include "math.h"
22 #include "math_private.h"
23
24 static const float
25 ln2_hi = 6.9313812256e-01, /* 0x3f317180 */
26 ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */
27 two25 = 3.355443200e+07, /* 0x4c000000 */
28 Lp1 = 6.6666668653e-01, /* 3F2AAAAB */
29 Lp2 = 4.0000000596e-01, /* 3ECCCCCD */
30 Lp3 = 2.8571429849e-01, /* 3E924925 */
31 Lp4 = 2.2222198546e-01, /* 3E638E29 */
32 Lp5 = 1.8183572590e-01, /* 3E3A3325 */
33 Lp6 = 1.5313838422e-01, /* 3E1CD04F */
34 Lp7 = 1.4798198640e-01; /* 3E178897 */
35
36 static const float zero = 0.0;
37
38 float
log1pf(float x)39 log1pf(float x)
40 {
41 float hfsq,f,c,s,z,R,u;
42 int32_t k,hx,hu,ax;
43
44 GET_FLOAT_WORD(hx,x);
45 ax = hx&0x7fffffff;
46
47 k = 1;
48 if (hx < 0x3ed413d0) { /* 1+x < sqrt(2)+ */
49 if(ax>=0x3f800000) { /* x <= -1.0 */
50 if(x==(float)-1.0) return -two25/zero; /* log1p(-1)=+inf */
51 else return (x-x)/(x-x); /* log1p(x<-1)=NaN */
52 }
53 if(ax<0x38000000) { /* |x| < 2**-15 */
54 if(two25+x>zero /* raise inexact */
55 &&ax<0x33800000) /* |x| < 2**-24 */
56 return x;
57 else
58 return x - x*x*(float)0.5;
59 }
60 if(hx>0||hx<=((int32_t)0xbe95f619)) {
61 k=0;f=x;hu=1;} /* sqrt(2)/2- <= 1+x < sqrt(2)+ */
62 }
63 if (hx >= 0x7f800000) return x+x;
64 if(k!=0) {
65 if(hx<0x5a000000) {
66 STRICT_ASSIGN(float,u,(float)1.0+x);
67 GET_FLOAT_WORD(hu,u);
68 k = (hu>>23)-127;
69 /* correction term */
70 c = (k>0)? (float)1.0-(u-x):x-(u-(float)1.0);
71 c /= u;
72 } else {
73 u = x;
74 GET_FLOAT_WORD(hu,u);
75 k = (hu>>23)-127;
76 c = 0;
77 }
78 hu &= 0x007fffff;
79 /*
80 * The approximation to sqrt(2) used in thresholds is not
81 * critical. However, the ones used above must give less
82 * strict bounds than the one here so that the k==0 case is
83 * never reached from here, since here we have committed to
84 * using the correction term but don't use it if k==0.
85 */
86 if(hu<0x3504f4) { /* u < sqrt(2) */
87 SET_FLOAT_WORD(u,hu|0x3f800000);/* normalize u */
88 } else {
89 k += 1;
90 SET_FLOAT_WORD(u,hu|0x3f000000); /* normalize u/2 */
91 hu = (0x00800000-hu)>>2;
92 }
93 f = u-(float)1.0;
94 }
95 hfsq=(float)0.5*f*f;
96 if(hu==0) { /* |f| < 2**-20 */
97 if(f==zero) {
98 if(k==0) {
99 return zero;
100 } else {
101 c += k*ln2_lo;
102 return k*ln2_hi+c;
103 }
104 }
105 R = hfsq*((float)1.0-(float)0.66666666666666666*f);
106 if(k==0) return f-R; else
107 return k*ln2_hi-((R-(k*ln2_lo+c))-f);
108 }
109 s = f/((float)2.0+f);
110 z = s*s;
111 R = z*(Lp1+z*(Lp2+z*(Lp3+z*(Lp4+z*(Lp5+z*(Lp6+z*Lp7))))));
112 if(k==0) return f-(hfsq-s*(hfsq+R)); else
113 return k*ln2_hi-((hfsq-(s*(hfsq+R)+(k*ln2_lo+c)))-f);
114 }
115