e_expf.c revision 17141
1/* e_expf.c -- float version of e_exp.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#ifndef lint 17static char rcsid[] = "$Id: e_expf.c,v 1.2 1995/05/30 05:48:09 rgrimes Exp $"; 18#endif 19 20#include "math.h" 21#include "math_private.h" 22 23#ifdef __STDC__ 24static const float 25#else 26static float 27#endif 28one = 1.0, 29halF[2] = {0.5,-0.5,}, 30huge = 1.0e+30, 31twom100 = 7.8886090522e-31, /* 2**-100=0x0d800000 */ 32o_threshold= 8.8721679688e+01, /* 0x42b17180 */ 33u_threshold= -1.0397208405e+02, /* 0xc2cff1b5 */ 34ln2HI[2] ={ 6.9313812256e-01, /* 0x3f317180 */ 35 -6.9313812256e-01,}, /* 0xbf317180 */ 36ln2LO[2] ={ 9.0580006145e-06, /* 0x3717f7d1 */ 37 -9.0580006145e-06,}, /* 0xb717f7d1 */ 38invln2 = 1.4426950216e+00, /* 0x3fb8aa3b */ 39P1 = 1.6666667163e-01, /* 0x3e2aaaab */ 40P2 = -2.7777778450e-03, /* 0xbb360b61 */ 41P3 = 6.6137559770e-05, /* 0x388ab355 */ 42P4 = -1.6533901999e-06, /* 0xb5ddea0e */ 43P5 = 4.1381369442e-08; /* 0x3331bb4c */ 44 45#ifdef __STDC__ 46 float __ieee754_expf(float x) /* default IEEE double exp */ 47#else 48 float __ieee754_expf(x) /* default IEEE double exp */ 49 float x; 50#endif 51{ 52 float y,hi=0.0,lo=0.0,c,t; 53 int32_t k=0,xsb; 54 u_int32_t hx; 55 56 GET_FLOAT_WORD(hx,x); 57 xsb = (hx>>31)&1; /* sign bit of x */ 58 hx &= 0x7fffffff; /* high word of |x| */ 59 60 /* filter out non-finite argument */ 61 if(hx >= 0x42b17218) { /* if |x|>=88.721... */ 62 if(hx>0x7f800000) 63 return x+x; /* NaN */ 64 if(hx==0x7f800000) 65 return (xsb==0)? x:0.0; /* exp(+-inf)={inf,0} */ 66 if(x > o_threshold) return huge*huge; /* overflow */ 67 if(x < u_threshold) return twom100*twom100; /* underflow */ 68 } 69 70 /* argument reduction */ 71 if(hx > 0x3eb17218) { /* if |x| > 0.5 ln2 */ 72 if(hx < 0x3F851592) { /* and |x| < 1.5 ln2 */ 73 hi = x-ln2HI[xsb]; lo=ln2LO[xsb]; k = 1-xsb-xsb; 74 } else { 75 k = invln2*x+halF[xsb]; 76 t = k; 77 hi = x - t*ln2HI[0]; /* t*ln2HI is exact here */ 78 lo = t*ln2LO[0]; 79 } 80 x = hi - lo; 81 } 82 else if(hx < 0x31800000) { /* when |x|<2**-28 */ 83 if(huge+x>one) return one+x;/* trigger inexact */ 84 } 85 else k = 0; 86 87 /* x is now in primary range */ 88 t = x*x; 89 c = x - t*(P1+t*(P2+t*(P3+t*(P4+t*P5)))); 90 if(k==0) return one-((x*c)/(c-(float)2.0)-x); 91 else y = one-((lo-(x*c)/((float)2.0-c))-hi); 92 if(k >= -125) { 93 u_int32_t hy; 94 GET_FLOAT_WORD(hy,y); 95 SET_FLOAT_WORD(y,hy+(k<<23)); /* add k to y's exponent */ 96 return y; 97 } else { 98 u_int32_t hy; 99 GET_FLOAT_WORD(hy,y); 100 SET_FLOAT_WORD(y,hy+((k+100)<<23)); /* add k to y's exponent */ 101 return y*twom100; 102 } 103} 104