1 /* ef_exp.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 #include "fdlibm.h" 17 18 #ifdef __v810__ 19 #define const 20 #endif 21 22 #ifdef __STDC__ 23 static const float 24 #else 25 static float 26 #endif 27 one = 1.0, 28 halF[2] = {0.5,-0.5,}, 29 huge = 1.0e+30, 30 twom100 = 7.8886090522e-31, /* 2**-100=0x0d800000 */ 31 ln2HI[2] ={ 6.9313812256e-01, /* 0x3f317180 */ 32 -6.9313812256e-01,}, /* 0xbf317180 */ 33 ln2LO[2] ={ 9.0580006145e-06, /* 0x3717f7d1 */ 34 -9.0580006145e-06,}, /* 0xb717f7d1 */ 35 invln2 = 1.4426950216e+00, /* 0x3fb8aa3b */ 36 P1 = 1.6666667163e-01, /* 0x3e2aaaab */ 37 P2 = -2.7777778450e-03, /* 0xbb360b61 */ 38 P3 = 6.6137559770e-05, /* 0x388ab355 */ 39 P4 = -1.6533901999e-06, /* 0xb5ddea0e */ 40 P5 = 4.1381369442e-08; /* 0x3331bb4c */ 41 42 #ifdef __STDC__ __ieee754_expf(float x)43 float __ieee754_expf(float x) /* default IEEE double exp */ 44 #else 45 float __ieee754_expf(x) /* default IEEE double exp */ 46 float x; 47 #endif 48 { 49 float y,hi,lo,c,t; 50 __int32_t k = 0,xsb,sx; 51 __uint32_t hx; 52 53 GET_FLOAT_WORD(sx,x); 54 xsb = (sx>>31)&1; /* sign bit of x */ 55 hx = sx & 0x7fffffff; /* high word of |x| */ 56 57 /* filter out non-finite argument */ 58 if(FLT_UWORD_IS_NAN(hx)) 59 return x+x; /* NaN */ 60 if(FLT_UWORD_IS_INFINITE(hx)) 61 return (xsb==0)? x:0.0; /* exp(+-inf)={inf,0} */ 62 if(sx > FLT_UWORD_LOG_MAX) 63 return huge*huge; /* overflow */ 64 if(sx < 0 && hx > FLT_UWORD_LOG_MIN) 65 return twom100*twom100; /* underflow */ 66 67 /* argument reduction */ 68 if(hx > 0x3eb17218) { /* if |x| > 0.5 ln2 */ 69 if(hx < 0x3F851592) { /* and |x| < 1.5 ln2 */ 70 hi = x-ln2HI[xsb]; lo=ln2LO[xsb]; k = 1-xsb-xsb; 71 } else { 72 k = invln2*x+halF[xsb]; 73 t = k; 74 hi = x - t*ln2HI[0]; /* t*ln2HI is exact here */ 75 lo = t*ln2LO[0]; 76 } 77 x = hi - lo; 78 } 79 else if(hx < 0x31800000) { /* when |x|<2**-28 */ 80 if(huge+x>one) return one+x;/* trigger inexact */ 81 } 82 83 /* x is now in primary range */ 84 t = x*x; 85 c = x - t*(P1+t*(P2+t*(P3+t*(P4+t*P5)))); 86 if(k==0) return one-((x*c)/(c-(float)2.0)-x); 87 else y = one-((lo-(x*c)/((float)2.0-c))-hi); 88 if(k >= -125) { 89 __uint32_t hy; 90 GET_FLOAT_WORD(hy,y); 91 SET_FLOAT_WORD(y,hy+(k<<23)); /* add k to y's exponent */ 92 return y; 93 } else { 94 __uint32_t hy; 95 GET_FLOAT_WORD(hy,y); 96 SET_FLOAT_WORD(y,hy+((k+100)<<23)); /* add k to y's exponent */ 97 return y*twom100; 98 } 99 } 100