1 | /* s_log1pf.c -- float version of s_log1p.c. |
2 | */ |
3 | |
4 | /* |
5 | * ==================================================== |
6 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
7 | * |
8 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
9 | * Permission to use, copy, modify, and distribute this |
10 | * software is freely granted, provided that this notice |
11 | * is preserved. |
12 | * ==================================================== |
13 | */ |
14 | |
15 | #include <float.h> |
16 | #include <math.h> |
17 | #include <math-barriers.h> |
18 | #include <math_private.h> |
19 | #include <math-underflow.h> |
20 | #include <libc-diag.h> |
21 | |
22 | static const float |
23 | ln2_hi = 6.9313812256e-01, /* 0x3f317180 */ |
24 | ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */ |
25 | two25 = 3.355443200e+07, /* 0x4c000000 */ |
26 | Lp1 = 6.6666668653e-01, /* 3F2AAAAB */ |
27 | Lp2 = 4.0000000596e-01, /* 3ECCCCCD */ |
28 | Lp3 = 2.8571429849e-01, /* 3E924925 */ |
29 | Lp4 = 2.2222198546e-01, /* 3E638E29 */ |
30 | Lp5 = 1.8183572590e-01, /* 3E3A3325 */ |
31 | Lp6 = 1.5313838422e-01, /* 3E1CD04F */ |
32 | Lp7 = 1.4798198640e-01; /* 3E178897 */ |
33 | |
34 | static const float zero = 0.0; |
35 | |
36 | float |
37 | __log1pf(float x) |
38 | { |
39 | float hfsq,f,c,s,z,R,u; |
40 | int32_t k,hx,hu,ax; |
41 | |
42 | GET_FLOAT_WORD(hx,x); |
43 | ax = hx&0x7fffffff; |
44 | |
45 | k = 1; |
46 | if (hx < 0x3ed413d7) { /* x < 0.41422 */ |
47 | if(ax>=0x3f800000) { /* x <= -1.0 */ |
48 | if(x==(float)-1.0) return -two25/zero; /* log1p(-1)=-inf */ |
49 | else return (x-x)/(x-x); /* log1p(x<-1)=NaN */ |
50 | } |
51 | if(ax<0x31000000) { /* |x| < 2**-29 */ |
52 | math_force_eval(two25+x); /* raise inexact */ |
53 | if (ax<0x24800000) /* |x| < 2**-54 */ |
54 | { |
55 | math_check_force_underflow (x); |
56 | return x; |
57 | } |
58 | else |
59 | return x - x*x*(float)0.5; |
60 | } |
61 | if(hx>0||hx<=((int32_t)0xbe95f61f)) { |
62 | k=0;f=x;hu=1;} /* -0.2929<x<0.41422 */ |
63 | } |
64 | if (hx >= 0x7f800000) return x+x; |
65 | if(k!=0) { |
66 | if(hx<0x5a000000) { |
67 | u = (float)1.0+x; |
68 | GET_FLOAT_WORD(hu,u); |
69 | k = (hu>>23)-127; |
70 | /* correction term */ |
71 | c = (k>0)? (float)1.0-(u-x):x-(u-(float)1.0); |
72 | c /= u; |
73 | } else { |
74 | u = x; |
75 | GET_FLOAT_WORD(hu,u); |
76 | k = (hu>>23)-127; |
77 | c = 0; |
78 | } |
79 | hu &= 0x007fffff; |
80 | if(hu<0x3504f7) { |
81 | SET_FLOAT_WORD(u,hu|0x3f800000);/* normalize u */ |
82 | } else { |
83 | k += 1; |
84 | SET_FLOAT_WORD(u,hu|0x3f000000); /* normalize u/2 */ |
85 | hu = (0x00800000-hu)>>2; |
86 | } |
87 | f = u-(float)1.0; |
88 | } |
89 | hfsq=(float)0.5*f*f; |
90 | if(hu==0) { /* |f| < 2**-20 */ |
91 | if(f==zero) { |
92 | if(k==0) return zero; |
93 | else {c += k*ln2_lo; return k*ln2_hi+c;} |
94 | } |
95 | R = hfsq*(1.0f-0.66666666666666666f*f); |
96 | if(k==0) return f-R; else |
97 | return k*ln2_hi-((R-(k*ln2_lo+c))-f); |
98 | } |
99 | s = f/((float)2.0+f); |
100 | z = s*s; |
101 | R = z*(Lp1+z*(Lp2+z*(Lp3+z*(Lp4+z*(Lp5+z*(Lp6+z*Lp7)))))); |
102 | if (k == 0) |
103 | return f - (hfsq - s * (hfsq + R)); |
104 | else |
105 | { |
106 | /* With GCC 7 when compiling with -Os the compiler warns |
107 | that c might be used uninitialized. This can't be true |
108 | because k must be 0 for c to be uninitialized and we |
109 | handled that computation earlier without using c. */ |
110 | DIAG_PUSH_NEEDS_COMMENT; |
111 | DIAG_IGNORE_Os_NEEDS_COMMENT (7, "-Wmaybe-uninitialized" ); |
112 | return k * ln2_hi - ((hfsq - (s * (hfsq + R) |
113 | + (k * ln2_lo + c))) - f); |
114 | DIAG_POP_NEEDS_COMMENT; |
115 | } |
116 | } |
117 | |