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 #ifndef lint 17 static char rcsid[] = "$FreeBSD$"; 18 #endif 19 20 #include "math.h" 21 #include "math_private.h" 22 23 /* cbrtf(x) 24 * Return cube root of x 25 */ 26 static const unsigned 27 B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */ 28 B2 = 642849266; /* B2 = (76+2/3-0.03306235651)*2**23 */ 29 30 static const float 31 C = 5.4285717010e-01, /* 19/35 = 0x3f0af8b0 */ 32 D = -7.0530611277e-01, /* -864/1225 = 0xbf348ef1 */ 33 E = 1.4142856598e+00, /* 99/70 = 0x3fb50750 */ 34 F = 1.6071428061e+00, /* 45/28 = 0x3fcdb6db */ 35 G = 3.5714286566e-01; /* 5/14 = 0x3eb6db6e */ 36 37 float 38 cbrtf(float x) 39 { 40 float r,s,t; 41 int32_t hx; 42 u_int32_t sign; 43 u_int32_t high; 44 45 GET_FLOAT_WORD(hx,x); 46 sign=hx&0x80000000; /* sign= sign(x) */ 47 hx ^=sign; 48 if(hx>=0x7f800000) return(x+x); /* cbrt(NaN,INF) is itself */ 49 if(hx==0) 50 return(x); /* cbrt(0) is itself */ 51 52 SET_FLOAT_WORD(x,hx); /* x <- |x| */ 53 /* rough cbrt to 5 bits */ 54 if(hx<0x00800000) /* subnormal number */ 55 {SET_FLOAT_WORD(t,0x4b800000); /* set t= 2**24 */ 56 t*=x; GET_FLOAT_WORD(high,t); SET_FLOAT_WORD(t,high/3+B2); 57 } 58 else 59 SET_FLOAT_WORD(t,hx/3+B1); 60 61 62 /* new cbrt to 23 bits */ 63 r=t*t/x; 64 s=C+r*t; 65 t*=G+F/(s+E+D/s); 66 67 /* retore the sign bit */ 68 GET_FLOAT_WORD(high,t); 69 SET_FLOAT_WORD(t,high|sign); 70 return(t); 71 } 72