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 1.7 1999/07/02 15:37:43 simonb Exp $"); 19 #endif 20 21 #include "math.h" 22 #include "math_private.h" 23 24 #ifdef __STDC__ 25 static const float 26 #else 27 static float 28 #endif 29 ln2_hi = 6.9313812256e-01, /* 0x3f317180 */ 30 ln2_lo = 9.0580006145e-06, /* 0x3717f7d1 */ 31 two25 = 3.355443200e+07, /* 0x4c000000 */ 32 Lp1 = 6.6666668653e-01, /* 3F2AAAAB */ 33 Lp2 = 4.0000000596e-01, /* 3ECCCCCD */ 34 Lp3 = 2.8571429849e-01, /* 3E924925 */ 35 Lp4 = 2.2222198546e-01, /* 3E638E29 */ 36 Lp5 = 1.8183572590e-01, /* 3E3A3325 */ 37 Lp6 = 1.5313838422e-01, /* 3E1CD04F */ 38 Lp7 = 1.4798198640e-01; /* 3E178897 */ 39 40 #ifdef __STDC__ 41 static const float zero = 0.0; 42 #else 43 static float zero = 0.0; 44 #endif 45 46 #ifdef __STDC__ 47 float log1pf(float x) 48 #else 49 float log1pf(x) 50 float x; 51 #endif 52 { 53 float hfsq,f,c,s,z,R,u; 54 int32_t k,hx,hu,ax; 55 56 f = c = 0; 57 hu = 0; 58 GET_FLOAT_WORD(hx,x); 59 ax = hx&0x7fffffff; 60 61 k = 1; 62 if (hx < 0x3ed413d7) { /* x < 0.41422 */ 63 if(ax>=0x3f800000) { /* x <= -1.0 */ 64 if(x==(float)-1.0) return -two25/zero; /* log1p(-1)=+inf */ 65 else return (x-x)/(x-x); /* log1p(x<-1)=NaN */ 66 } 67 if(ax<0x31000000) { /* |x| < 2**-29 */ 68 if(two25+x>zero /* raise inexact */ 69 &&ax<0x24800000) /* |x| < 2**-54 */ 70 return x; 71 else 72 return x - x*x*(float)0.5; 73 } 74 if(hx>0||hx<=((int32_t)0xbe95f61f)) { 75 k=0;f=x;hu=1;} /* -0.2929<x<0.41422 */ 76 } 77 if (hx >= 0x7f800000) return x+x; 78 if(k!=0) { 79 if(hx<0x5a000000) { 80 u = (float)1.0+x; 81 GET_FLOAT_WORD(hu,u); 82 k = (hu>>23)-127; 83 /* correction term */ 84 c = (k>0)? (float)1.0-(u-x):x-(u-(float)1.0); 85 c /= u; 86 } else { 87 u = x; 88 GET_FLOAT_WORD(hu,u); 89 k = (hu>>23)-127; 90 c = 0; 91 } 92 hu &= 0x007fffff; 93 if(hu<0x3504f7) { 94 SET_FLOAT_WORD(u,hu|0x3f800000);/* normalize u */ 95 } else { 96 k += 1; 97 SET_FLOAT_WORD(u,hu|0x3f000000); /* normalize u/2 */ 98 hu = (0x00800000-hu)>>2; 99 } 100 f = u-(float)1.0; 101 } 102 hfsq=(float)0.5*f*f; 103 if(hu==0) { /* |f| < 2**-20 */ 104 if(f==zero) { if(k==0) return zero; 105 else {c += k*ln2_lo; return k*ln2_hi+c;} 106 } 107 R = hfsq*((float)1.0-(float)0.66666666666666666*f); 108 if(k==0) return f-R; else 109 return k*ln2_hi-((R-(k*ln2_lo+c))-f); 110 } 111 s = f/((float)2.0+f); 112 z = s*s; 113 R = z*(Lp1+z*(Lp2+z*(Lp3+z*(Lp4+z*(Lp5+z*(Lp6+z*Lp7)))))); 114 if(k==0) return f-(hfsq-s*(hfsq+R)); else 115 return k*ln2_hi-((hfsq-(s*(hfsq+R)+(k*ln2_lo+c)))-f); 116 } 117