1 /* s_cbrtf.c -- float version of s_cbrt.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 "math.h" 17 #include "math_private.h" 18 19 /* cbrtf(x) 20 * Return cube root of x 21 */ 22 static const unsigned 23 B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */ 24 B2 = 642849266; /* B2 = (76+2/3-0.03306235651)*2**23 */ 25 26 static const float 27 C = 5.4285717010e-01, /* 19/35 = 0x3f0af8b0 */ 28 D = -7.0530611277e-01, /* -864/1225 = 0xbf348ef1 */ 29 E = 1.4142856598e+00, /* 99/70 = 0x3fb50750 */ 30 F = 1.6071428061e+00, /* 45/28 = 0x3fcdb6db */ 31 G = 3.5714286566e-01; /* 5/14 = 0x3eb6db6e */ 32 33 float 34 cbrtf(float x) 35 { 36 float r,s,t; 37 int32_t hx; 38 u_int32_t sign; 39 u_int32_t high; 40 41 GET_FLOAT_WORD(hx,x); 42 sign=hx&0x80000000; /* sign= sign(x) */ 43 hx ^=sign; 44 if(hx>=0x7f800000) return(x+x); /* cbrt(NaN,INF) is itself */ 45 if(hx==0) 46 return(x); /* cbrt(0) is itself */ 47 48 SET_FLOAT_WORD(x,hx); /* x <- |x| */ 49 /* rough cbrt to 5 bits */ 50 if(hx<0x00800000) /* subnormal number */ 51 {SET_FLOAT_WORD(t,0x4b800000); /* set t= 2**24 */ 52 t*=x; GET_FLOAT_WORD(high,t); SET_FLOAT_WORD(t,high/3+B2); 53 } 54 else 55 SET_FLOAT_WORD(t,hx/3+B1); 56 57 58 /* new cbrt to 23 bits */ 59 r=t*t/x; 60 s=C+r*t; 61 t*=G+F/(s+E+D/s); 62 63 /* retore the sign bit */ 64 GET_FLOAT_WORD(high,t); 65 SET_FLOAT_WORD(t,high|sign); 66 return(t); 67 } 68