From 0b44a0315b47dd8eced9f3b7f31580cf14bbfc01 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Sat, 12 Feb 2011 00:22:29 -0500 Subject: initial check-in, version 0.5.0 --- src/math/s_cbrtf.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 src/math/s_cbrtf.c (limited to 'src/math/s_cbrtf.c') diff --git a/src/math/s_cbrtf.c b/src/math/s_cbrtf.c new file mode 100644 index 00000000..e7b46de7 --- /dev/null +++ b/src/math/s_cbrtf.c @@ -0,0 +1,67 @@ +/* s_cbrtf.c -- float version of s_cbrt.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 +#include "math_private.h" + +/* cbrtf(x) + * Return cube root of x + */ +static const unsigned + B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */ + B2 = 642849266; /* B2 = (76+2/3-0.03306235651)*2**23 */ + +static const float +C = 5.4285717010e-01, /* 19/35 = 0x3f0af8b0 */ +D = -7.0530611277e-01, /* -864/1225 = 0xbf348ef1 */ +E = 1.4142856598e+00, /* 99/70 = 0x3fb50750 */ +F = 1.6071428061e+00, /* 45/28 = 0x3fcdb6db */ +G = 3.5714286566e-01; /* 5/14 = 0x3eb6db6e */ + +float +cbrtf(float x) +{ + float r,s,t; + int32_t hx; + uint32_t sign; + uint32_t high; + + GET_FLOAT_WORD(hx,x); + sign=hx&0x80000000; /* sign= sign(x) */ + hx ^=sign; + if(hx>=0x7f800000) return(x+x); /* cbrt(NaN,INF) is itself */ + if(hx==0) + return(x); /* cbrt(0) is itself */ + + SET_FLOAT_WORD(x,hx); /* x <- |x| */ + /* rough cbrt to 5 bits */ + if(hx<0x00800000) /* subnormal number */ + {SET_FLOAT_WORD(t,0x4b800000); /* set t= 2**24 */ + t*=x; GET_FLOAT_WORD(high,t); SET_FLOAT_WORD(t,high/3+B2); + } + else + SET_FLOAT_WORD(t,hx/3+B1); + + + /* new cbrt to 23 bits */ + r=t*t/x; + s=C+r*t; + t*=G+F/(s+E+D/s); + + /* retore the sign bit */ + GET_FLOAT_WORD(high,t); + SET_FLOAT_WORD(t,high|sign); + return(t); +} -- cgit v1.2.1