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71 lines
1.7 KiB
C
71 lines
1.7 KiB
C
/* s_cbrtf.c -- float version of s_cbrt.c.
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* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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*/
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#ifndef lint
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static char rcsid[] = "$FreeBSD$";
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#endif
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#include "math.h"
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#include "math_private.h"
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/* cbrtf(x)
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* Return cube root of x
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*/
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static const unsigned
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B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */
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B2 = 642849266; /* B2 = (76+2/3-0.03306235651)*2**23 */
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static const float
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C = 5.4285717010e-01, /* 19/35 = 0x3f0af8b0 */
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D = -7.0530611277e-01, /* -864/1225 = 0xbf348ef1 */
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E = 1.4142856598e+00, /* 99/70 = 0x3fb50750 */
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F = 1.6071428061e+00, /* 45/28 = 0x3fcdb6db */
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G = 3.5714286566e-01; /* 5/14 = 0x3eb6db6e */
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float cbrtf(float x)
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{
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float r,s,t;
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int32_t hx;
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u_int32_t sign;
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u_int32_t high;
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GET_FLOAT_WORD(hx,x);
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sign=hx&0x80000000; /* sign= sign(x) */
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hx ^=sign;
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if(hx>=0x7f800000) return(x+x); /* cbrt(NaN,INF) is itself */
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if(hx==0)
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return(x); /* cbrt(0) is itself */
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SET_FLOAT_WORD(x,hx); /* x <- |x| */
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/* rough cbrt to 5 bits */
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if(hx<0x00800000) /* subnormal number */
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{SET_FLOAT_WORD(t,0x4b800000); /* set t= 2**24 */
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t*=x; GET_FLOAT_WORD(high,t); SET_FLOAT_WORD(t,high/3+B2);
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}
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else
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SET_FLOAT_WORD(t,hx/3+B1);
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/* new cbrt to 23 bits */
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r=t*t/x;
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s=C+r*t;
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t*=G+F/(s+E+D/s);
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/* retore the sign bit */
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GET_FLOAT_WORD(high,t);
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SET_FLOAT_WORD(t,high|sign);
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return(t);
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}
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