e_expf.c revision 142369
12116Sjkh/* e_expf.c -- float version of e_exp.c. 22116Sjkh * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 32116Sjkh */ 42116Sjkh 52116Sjkh/* 62116Sjkh * ==================================================== 72116Sjkh * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 82116Sjkh * 92116Sjkh * Developed at SunPro, a Sun Microsystems, Inc. business. 102116Sjkh * Permission to use, copy, modify, and distribute this 118870Srgrimes * software is freely granted, provided that this notice 122116Sjkh * is preserved. 132116Sjkh * ==================================================== 142116Sjkh */ 152116Sjkh 162116Sjkh#ifndef lint 1750476Speterstatic char rcsid[] = "$FreeBSD: head/lib/msun/src/e_expf.c 142369 2005-02-24 06:32:13Z das $"; 182116Sjkh#endif 192116Sjkh 202116Sjkh#include "math.h" 212116Sjkh#include "math_private.h" 222116Sjkh 232116Sjkhstatic const float 242116Sjkhone = 1.0, 252116SjkhhalF[2] = {0.5,-0.5,}, 262116Sjkhhuge = 1.0e+30, 272116Sjkhtwom100 = 7.8886090522e-31, /* 2**-100=0x0d800000 */ 282116Sjkho_threshold= 8.8721679688e+01, /* 0x42b17180 */ 292116Sjkhu_threshold= -1.0397208405e+02, /* 0xc2cff1b5 */ 30142369Sdasln2HI[2] ={ 6.9313812256e-01, /* 0x3f317180 */ 31142369Sdas -6.9313812256e-01,}, /* 0xbf317180 */ 32142369Sdasln2LO[2] ={ 9.0580006145e-06, /* 0x3717f7d1 */ 33142369Sdas -9.0580006145e-06,}, /* 0xb717f7d1 */ 342116Sjkhinvln2 = 1.4426950216e+00, /* 0x3fb8aa3b */ 352116SjkhP1 = 1.6666667163e-01, /* 0x3e2aaaab */ 362116SjkhP2 = -2.7777778450e-03, /* 0xbb360b61 */ 372116SjkhP3 = 6.6137559770e-05, /* 0x388ab355 */ 382116SjkhP4 = -1.6533901999e-06, /* 0xb5ddea0e */ 392116SjkhP5 = 4.1381369442e-08; /* 0x3331bb4c */ 402116Sjkh 4197407Salfredfloat 42142369Sdas__ieee754_expf(float x) /* default IEEE double exp */ 432116Sjkh{ 44142369Sdas float y,hi=0.0,lo=0.0,c,t; 4517141Sjkh int32_t k=0,xsb; 462116Sjkh u_int32_t hx; 472116Sjkh 482116Sjkh GET_FLOAT_WORD(hx,x); 492116Sjkh xsb = (hx>>31)&1; /* sign bit of x */ 50142369Sdas hx &= 0x7fffffff; /* high word of |x| */ 512116Sjkh 522116Sjkh /* filter out non-finite argument */ 532116Sjkh if(hx >= 0x42b17218) { /* if |x|>=88.721... */ 542116Sjkh if(hx>0x7f800000) 552116Sjkh return x+x; /* NaN */ 562116Sjkh if(hx==0x7f800000) 572116Sjkh return (xsb==0)? x:0.0; /* exp(+-inf)={inf,0} */ 582116Sjkh if(x > o_threshold) return huge*huge; /* overflow */ 592116Sjkh if(x < u_threshold) return twom100*twom100; /* underflow */ 602116Sjkh } 612116Sjkh 622116Sjkh /* argument reduction */ 638870Srgrimes if(hx > 0x3eb17218) { /* if |x| > 0.5 ln2 */ 642116Sjkh if(hx < 0x3F851592) { /* and |x| < 1.5 ln2 */ 65142369Sdas hi = x-ln2HI[xsb]; lo=ln2LO[xsb]; k = 1-xsb-xsb; 662116Sjkh } else { 672116Sjkh k = invln2*x+halF[xsb]; 682116Sjkh t = k; 69142369Sdas hi = x - t*ln2HI[0]; /* t*ln2HI is exact here */ 70142369Sdas lo = t*ln2LO[0]; 712116Sjkh } 72142369Sdas x = hi - lo; 738870Srgrimes } 742116Sjkh else if(hx < 0x31800000) { /* when |x|<2**-28 */ 752116Sjkh if(huge+x>one) return one+x;/* trigger inexact */ 762116Sjkh } 772116Sjkh else k = 0; 782116Sjkh 792116Sjkh /* x is now in primary range */ 802116Sjkh t = x*x; 812116Sjkh c = x - t*(P1+t*(P2+t*(P3+t*(P4+t*P5)))); 82142369Sdas if(k==0) return one-((x*c)/(c-(float)2.0)-x); 83142369Sdas else y = one-((lo-(x*c)/((float)2.0-c))-hi); 842116Sjkh if(k >= -125) { 852116Sjkh u_int32_t hy; 862116Sjkh GET_FLOAT_WORD(hy,y); 872116Sjkh SET_FLOAT_WORD(y,hy+(k<<23)); /* add k to y's exponent */ 882116Sjkh return y; 892116Sjkh } else { 902116Sjkh u_int32_t hy; 912116Sjkh GET_FLOAT_WORD(hy,y); 922116Sjkh SET_FLOAT_WORD(y,hy+((k+100)<<23)); /* add k to y's exponent */ 932116Sjkh return y*twom100; 942116Sjkh } 952116Sjkh} 96