133 lines
3.6 KiB
C
133 lines
3.6 KiB
C
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/* @(#)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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FUNCTION
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<<rint>>, <<rintf>>--round to integer
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INDEX
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rint
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INDEX
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rintf
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ANSI_SYNOPSIS
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#include <math.h>
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double rint(double <[x]>);
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float rintf(float <[x]>);
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DESCRIPTION
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The <<rint>> functions round their argument to an integer value in
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floating-point format, using the current rounding direction. They
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raise the "inexact" floating-point exception if the result differs
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in value from the argument. See the <<nearbyint>> functions for the
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same function with the "inexact" floating-point exception never being
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raised. Newlib does not directly support floating-point exceptions.
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The <<rint>> functions are written so that the "inexact" exception is
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raised in hardware implementations that support it, even though Newlib
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does not provide access.
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RETURNS
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<[x]> rounded to an integral value, using the current rounding direction.
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PORTABILITY
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ANSI C, POSIX
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SEEALSO
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<<nearbyint>>, <<round>>
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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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* Whenever a fraction is present, if the second or any following bit after
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* the radix point is set, limit to the second radix point to avoid
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* possible double rounding in the TWO52 +- steps (in case guard bits are
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* used). Specifically, if have any, chop off bits past the 2nd place and
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* set the second place.
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* (e.g. 2.0625=0b10.0001 => 0b10.01=2.25;
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* 2.3125=0b10.011 => 0b10.01=2.25;
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* 1.5625= 0b1.1001 => 0b1.11=1.75;
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* 1.9375= 0b1.1111 => 0b1.11=1.75.
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* Pseudo-code: if(x.frac & ~0b0.10) x.frac = (x.frac & 0b0.11) | 0b0.01;).
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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 "fdlibm.h"
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#ifndef _DOUBLE_IS_32BITS
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#ifdef __STDC__
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static const double
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#else
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static double
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#endif
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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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#ifdef __STDC__
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double rint(double x)
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#else
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double rint(x)
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double x;
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#endif
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{
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__int32_t i0,j0,sx;
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__uint32_t i,i1;
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double t;
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volatile double w;
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EXTRACT_WORDS(i0,i1,x);
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sx = (i0>>31)&1; /* sign */
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j0 = ((i0>>20)&0x7ff)-0x3ff; /* exponent */
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if(j0<20) { /* no integral bits in LS part */
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if(j0<0) { /* x is fractional or 0 */
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if(((i0&0x7fffffff)|i1)==0) return x; /* x == 0 */
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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 { /* x has integer and maybe fraction */
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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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/* 2nd or any later bit after radix is set */
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if(j0==19) i1 = 0x80000000; else i1 = 0;
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i0 = (i0&(~i))|((0x40000)>>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 = ((__uint32_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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w = TWO52[sx]+x;
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return w-TWO52[sx];
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}
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#endif /* _DOUBLE_IS_32BITS */
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