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83 lines
1.7 KiB
C
83 lines
1.7 KiB
C
/* origin: FreeBSD /usr/src/lib/msun/src/s_floor.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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* floor(x)
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* Return x rounded toward -inf to integral value
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* Method:
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* Bit twiddling.
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* Exception:
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* Inexact flag raised if x not equal to floor(x).
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*/
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#include "libm.h"
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static const double huge = 1.0e300;
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double floor(double x)
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{
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int32_t i0,i1,j0;
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uint32_t i,j;
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EXTRACT_WORDS(i0, i1, x);
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// FIXME: signed shift
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j0 = ((i0>>20)&0x7ff) - 0x3ff;
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if (j0 < 20) {
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if (j0 < 0) { /* |x| < 1 */
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/* raise inexact if x != 0 */
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if (huge+x > 0.0) {
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if (i0 >= 0) { /* x >= 0 */
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i0 = i1 = 0;
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} else if (((i0&0x7fffffff)|i1) != 0) {
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i0 = 0xbff00000;
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i1 = 0;
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}
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}
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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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/* raise inexact flag */
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if (huge+x > 0.0) {
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if (i0 < 0)
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i0 += 0x00100000>>j0;
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i0 &= ~i;
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i1 = 0;
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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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else
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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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/* raise inexact flag */
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if (huge+x > 0.0) {
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if (i0 < 0) {
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if (j0 == 20)
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i0++;
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else {
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j = i1+(1<<(52-j0));
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if (j < i1)
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i0++; /* got a carry */
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i1 = j;
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}
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}
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i1 &= ~i;
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}
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}
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INSERT_WORDS(x, i0, i1);
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return x;
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}
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