/* e_powf.c -- float version of e_pow.c. * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunPro, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== */ #include "math.h" #include "math_private.h" static const volatile float huge = 1.0e+30, tiny = 1.0e-30; static const float bp[] = {1.0, 1.5,}, dp_h[] = { 0.0, 5.84960938e-01,}, /* 0x3f15c000 */ dp_l[] = { 0.0, 1.56322085e-06,}, /* 0x35d1cfdc */ zero = 0.0, one = 1.0, two = 2.0, two24 = 16777216.0, /* 0x4b800000 */ /* poly coefs for (3/2)*(log(x)-2s-2/3*s**3 */ L1 = 6.0000002384e-01, /* 0x3f19999a */ L2 = 4.2857143283e-01, /* 0x3edb6db7 */ L3 = 3.3333334327e-01, /* 0x3eaaaaab */ L4 = 2.7272811532e-01, /* 0x3e8ba305 */ L5 = 2.3066075146e-01, /* 0x3e6c3255 */ L6 = 2.0697501302e-01, /* 0x3e53f142 */ P1 = 1.6666667163e-01, /* 0x3e2aaaab */ P2 = -2.7777778450e-03, /* 0xbb360b61 */ P3 = 6.6137559770e-05, /* 0x388ab355 */ P4 = -1.6533901999e-06, /* 0xb5ddea0e */ P5 = 4.1381369442e-08, /* 0x3331bb4c */ lg2 = 6.9314718246e-01, /* 0x3f317218 */ lg2_h = 6.93145752e-01, /* 0x3f317200 */ lg2_l = 1.42860654e-06, /* 0x35bfbe8c */ ovt = 4.2995665694e-08, /* -(128-log2(ovfl+.5ulp)) */ cp = 9.6179670095e-01, /* 0x3f76384f =2/(3ln2) */ cp_h = 9.6179199219e-01, /* 0x3f763800 =head of cp */ cp_l = 4.7017383622e-06, /* 0x369dc3a0 =tail of cp_h */ ivln2 = 1.4426950216e+00, /* 0x3fb8aa3b =1/ln2 */ ivln2_h = 1.4426879883e+00, /* 0x3fb8aa00 =16b 1/ln2*/ ivln2_l = 7.0526075433e-06; /* 0x36eca570 =1/ln2 tail*/ float powf(float x, float y) { float z,ax,z_h,z_l,p_h,p_l; float yy1,t1,t2,r,s,t,u,v,w; int32_t i,j,k,yisint,n; int32_t hx,hy,ix,iy,is; GET_FLOAT_WORD(hx,x); GET_FLOAT_WORD(hy,y); ix = hx&0x7fffffff; iy = hy&0x7fffffff; /* y==zero: x**0 = 1 */ if(iy==0) return one; /* x==1: 1**y = 1, even if y is NaN */ if (hx==0x3f800000) return one; /* +-NaN return x+y */ if(ix > 0x7f800000 || iy > 0x7f800000) return x+y; /* determine if y is an odd int when x < 0 * yisint = 0 ... y is not an integer * yisint = 1 ... y is an odd int * yisint = 2 ... y is an even int */ yisint = 0; if(hx<0) { if(iy>=0x4b800000) yisint = 2; /* even integer y */ else if(iy>=0x3f800000) { k = (iy>>23)-0x7f; /* exponent */ j = iy>>(23-k); if((j<<(23-k))==iy) yisint = 2-(j&1); } } /* special value of y */ if (iy==0x7f800000) { /* y is +-inf */ if (ix==0x3f800000) return one; /* (-1)**+-inf is NaN */ else if (ix > 0x3f800000)/* (|x|>1)**+-inf = inf,0 */ return (hy>=0)? y: zero; else /* (|x|<1)**-,+inf = inf,0 */ return (hy<0)?-y: zero; } if(iy==0x3f800000) { /* y is +-1 */ if(hy<0) return one/x; else return x; } if(hy==0x40000000) return x*x; /* y is 2 */ if(hy==0x3f000000) { /* y is 0.5 */ if(hx>=0) /* x >= +0 */ return sqrtf(x); } ax = fabsf(x); /* special value of x */ if(ix==0x7f800000||ix==0||ix==0x3f800000){ z = ax; /*x is +-0,+-inf,+-1*/ if(hy<0) z = one/z; /* z = (1/|x|) */ if(hx<0) { if(((ix-0x3f800000)|yisint)==0) { z = (z-z)/(z-z); /* (-1)**non-int is NaN */ } else if(yisint==1) z = -z; /* (x<0)**odd = -(|x|**odd) */ } return z; } /* (x<0)**(non-int) is NaN */ if(((((u_int32_t)hx>>31)-1)|yisint)==0) return (x-x)/(x-x); /* |y| is huge */ if(iy>0x4d000000) { /* if |y| > 2**27 */ /* over/underflow if x is not close to one */ if(ix<0x3f7ffff8) return (hy<0)? huge*huge:tiny*tiny; if(ix>0x3f800007) return (hy>0)? huge*huge:tiny*tiny; /* now |1-x| is tiny <= 2**-20, suffice to compute log(x) by x-x^2/2+x^3/3-x^4/4 */ t = ax-one; /* t has 20 trailing zeros */ w = (t*t)*((float)0.5-t*((float)0.333333333333-t*(float)0.25)); u = ivln2_h*t; /* ivln2_h has 16 sig. bits */ v = t*ivln2_l-w*ivln2; t1 = u+v; GET_FLOAT_WORD(is,t1); SET_FLOAT_WORD(t1,is&0xfffff000); t2 = v-(t1-u); } else { float s2,s_h,s_l,t_h,t_l; n = 0; /* take care subnormal number */ if(ix<0x00800000) {ax *= two24; n -= 24; GET_FLOAT_WORD(ix,ax); } n += ((ix)>>23)-0x7f; j = ix&0x007fffff; /* determine interval */ ix = j|0x3f800000; /* normalize ix */ if(j<=0x1cc471) k=0; /* |x|>1)|0x20000000)+0x0040000+(k<<21)); t_l = ax - (t_h-bp[k]); s_l = v*((u-s_h*t_h)-s_h*t_l); /* compute log(ax) */ s2 = s*s; r = s2*s2*(L1+s2*(L2+s2*(L3+s2*(L4+s2*(L5+s2*L6))))); r += s_l*(s_h+s); s2 = s_h*s_h; t_h = (float)3.0+s2+r; GET_FLOAT_WORD(is,t_h); SET_FLOAT_WORD(t_h,is&0xfffff000); t_l = r-((t_h-(float)3.0)-s2); /* u+v = s*(1+...) */ u = s_h*t_h; v = s_l*t_h+t_l*s; /* 2/(3log2)*(s+...) */ p_h = u+v; GET_FLOAT_WORD(is,p_h); SET_FLOAT_WORD(p_h,is&0xfffff000); p_l = v-(p_h-u); z_h = cp_h*p_h; /* cp_h+cp_l = 2/(3*log2) */ z_l = cp_l*p_h+p_l*cp+dp_l[k]; /* log2(ax) = (s+..)*2/(3*log2) = n + dp_h + z_h + z_l */ t = (float)n; t1 = (((z_h+z_l)+dp_h[k])+t); GET_FLOAT_WORD(is,t1); SET_FLOAT_WORD(t1,is&0xfffff000); t2 = z_l-(((t1-t)-dp_h[k])-z_h); } s = one; /* s (sign of result -ve**odd) = -1 else = 1 */ if(((((u_int32_t)hx>>31)-1)|(yisint-1))==0) s = -one; /* (-ve)**(odd int) */ /* split up y into yy1+y2 and compute (yy1+y2)*(t1+t2) */ GET_FLOAT_WORD(is,y); SET_FLOAT_WORD(yy1,is&0xfffff000); p_l = (y-yy1)*t1+y*t2; p_h = yy1*t1; z = p_l+p_h; GET_FLOAT_WORD(j,z); if (j>0x43000000) /* if z > 128 */ return s*huge*huge; /* overflow */ else if (j==0x43000000) { /* if z == 128 */ if(p_l+ovt>z-p_h) return s*huge*huge; /* overflow */ } else if ((j&0x7fffffff)>0x43160000) /* z <= -150 */ return s*tiny*tiny; /* underflow */ else if (j==0xc3160000){ /* z == -150 */ if(p_l<=z-p_h) return s*tiny*tiny; /* underflow */ } /* * compute 2**(p_h+p_l) */ i = j&0x7fffffff; k = (i>>23)-0x7f; n = 0; if(i>0x3f000000) { /* if |z| > 0.5, set n = [z+0.5] */ n = j+(0x00800000>>(k+1)); k = ((n&0x7fffffff)>>23)-0x7f; /* new k for n */ SET_FLOAT_WORD(t,n&~(0x007fffff>>k)); n = ((n&0x007fffff)|0x00800000)>>(23-k); if(j<0) n = -n; p_h -= t; } t = p_l+p_h; GET_FLOAT_WORD(is,t); SET_FLOAT_WORD(t,is&0xfffff000); u = t*lg2_h; v = (p_l-(t-p_h))*lg2+t*lg2_l; z = u+v; w = v-(z-u); t = z*z; t1 = z - t*(P1+t*(P2+t*(P3+t*(P4+t*P5)))); r = (z*t1)/(t1-two)-(w+z*w); z = one-(r-z); GET_FLOAT_WORD(j,z); j += (n<<23); if((j>>23)<=0) z = scalbnf(z,n); /* subnormal output */ else SET_FLOAT_WORD(z,j); return s*z; } DEF_STD(powf);