mirror of
https://github.com/fluencelabs/musl
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91 lines
2.3 KiB
C
91 lines
2.3 KiB
C
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/* origin: FreeBSD /usr/src/lib/msun/src/s_rint.c */
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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 "libm.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 rint(double x)
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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 w,t;
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EXTRACT_WORDS(i0, i1, x);
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// FIXME: signed shift
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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)
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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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STRICT_ASSIGN(double, 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)
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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)
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i1 = 0x40000000;
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else if (j0 == 18)
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i1 = 0x80000000;
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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)
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return x+x; /* inf or NaN */
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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)
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return x; /* x is integral */
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i >>= 1;
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if ((i1&i) != 0)
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i1 = (i1 & ~i)|(0x40000000>>(j0-20));
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}
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INSERT_WORDS(x, i0, i1);
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STRICT_ASSIGN(double, w, TWO52[sx] + x);
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return w - TWO52[sx];
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}
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