Retro68/gcc/newlib/libm/common/sf_cbrt.c

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/* sf_cbrt.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 "fdlibm.h"
/* cbrtf(x)
* Return cube root of x
*/
#ifdef __STDC__
static const __uint32_t
#else
static __uint32_t
#endif
B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */
B2 = 642849266; /* B2 = (76+2/3-0.03306235651)*2**23 */
#ifdef __STDC__
static const float
#else
static float
#endif
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 */
#ifdef __STDC__
float cbrtf(float x)
#else
float cbrtf(x)
float x;
#endif
{
__int32_t hx;
float r,s,t;
__uint32_t sign;
__uint32_t high;
GET_FLOAT_WORD(hx,x);
sign=hx&0x80000000; /* sign= sign(x) */
hx ^=sign;
if(!FLT_UWORD_IS_FINITE(hx))
return(x+x); /* cbrt(NaN,INF) is itself */
if(FLT_UWORD_IS_ZERO(hx))
return(x); /* cbrt(0) is itself */
SET_FLOAT_WORD(x,hx); /* x <- |x| */
/* rough cbrt to 5 bits */
if(FLT_UWORD_IS_SUBNORMAL(hx)) /* 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);
}
#ifdef _DOUBLE_IS_32BITS
#ifdef __STDC__
double cbrt(double x)
#else
double cbrt(x)
double x;
#endif
{
return (double) cbrtf((float) x);
}
#endif /* defined(_DOUBLE_IS_32BITS) */