83 lines
2.2 KiB
C
83 lines
2.2 KiB
C
/* @(#)s_rint.c 5.1 93/09/24 */
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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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/*
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* rint(x)
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* Return x rounded to integral value according to the prevailing
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* rounding mode.
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* Method:
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* Using floating addition.
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* Exception:
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* Inexact flag raised if x not equal to rint(x).
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*/
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#include "math_private.h"
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static const double
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TWO52[2]={
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4.50359962737049600000e+15, /* 0x43300000, 0x00000000 */
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-4.50359962737049600000e+15, /* 0xC3300000, 0x00000000 */
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};
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double
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rint(double x)
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{
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i32_t i0,j0,sx;
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u32_t i,i1;
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double w,t;
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EXTRACT_WORDS(i0,i1,x);
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sx = (i0>>31)&1;
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j0 = ((i0>>20)&0x7ff)-0x3ff;
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if(j0<20) {
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if(j0<0) {
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if(((i0&0x7fffffff)|i1)==0) return x;
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i1 |= (i0&0x0fffff);
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i0 &= 0xfffe0000;
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i0 |= ((i1|-i1)>>12)&0x80000;
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SET_HIGH_WORD(x,i0);
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w = TWO52[sx]+x;
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t = w-TWO52[sx];
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GET_HIGH_WORD(i0,t);
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SET_HIGH_WORD(t,(i0&0x7fffffff)|(sx<<31));
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return t;
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} else {
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i = (0x000fffff)>>j0;
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if(((i0&i)|i1)==0) return x; /* x is integral */
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i>>=1;
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if(((i0&i)|i1)!=0) {
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/*
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* Some bit is set after the 0.5 bit. To avoid the
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* possibility of errors from double rounding in
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* w = TWO52[sx]+x, adjust the 0.25 bit to a lower
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* guard bit. We do this for all j0<=51. The
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* adjustment is trickiest for j0==18 and j0==19
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* since then it spans the word boundary.
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*/
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if(j0==19) i1 = 0x40000000; else
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if(j0==18) i1 = 0x80000000; else
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i0 = (i0&(~i))|((0x20000)>>j0);
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}
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}
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} else if (j0>51) {
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if(j0==0x400) return x+x; /* inf or NaN */
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else return x; /* x is integral */
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} else {
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i = ((u32_t)(0xffffffff))>>(j0-20);
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if((i1&i)==0) return x; /* x is integral */
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i>>=1;
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if((i1&i)!=0) i1 = (i1&(~i))|((0x40000000)>>(j0-20));
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}
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INSERT_WORDS(x,i0,i1);
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*(volatile double *)&w = TWO52[sx]+x; /* clip any extra precision */
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return w-TWO52[sx];
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}
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