116 lines
2.6 KiB
C
116 lines
2.6 KiB
C
/*
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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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<<round>>, <<roundf>>---round to integer, to nearest
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INDEX
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round
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INDEX
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roundf
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SYNOPSIS
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#include <math.h>
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double round(double <[x]>);
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float roundf(float <[x]>);
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DESCRIPTION
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The <<round>> functions round their argument to the nearest integer
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value in floating-point format, rounding halfway cases away from zero,
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regardless of the current rounding direction. (While the "inexact"
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floating-point exception behavior is unspecified by the C standard, the
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<<round>> functions are written so that "inexact" is not raised if the
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result does not equal the argument, which behavior is as recommended by
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IEEE 754 for its related functions.)
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RETURNS
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<[x]> rounded to an integral value.
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PORTABILITY
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ANSI C, POSIX
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SEEALSO
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<<nearbyint>>, <<rint>>
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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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double round(double x)
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#else
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double round(x)
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double x;
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#endif
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{
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/* Most significant word, least significant word. */
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__int32_t msw, exponent_less_1023;
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__uint32_t lsw;
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EXTRACT_WORDS(msw, lsw, x);
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/* Extract exponent field. */
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exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023;
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if (exponent_less_1023 < 20)
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{
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if (exponent_less_1023 < 0)
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{
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msw &= 0x80000000;
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if (exponent_less_1023 == -1)
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/* Result is +1.0 or -1.0. */
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msw |= ((__int32_t)1023 << 20);
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lsw = 0;
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}
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else
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{
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__uint32_t exponent_mask = 0x000fffff >> exponent_less_1023;
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if ((msw & exponent_mask) == 0 && lsw == 0)
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/* x in an integral value. */
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return x;
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msw += 0x00080000 >> exponent_less_1023;
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msw &= ~exponent_mask;
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lsw = 0;
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}
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}
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else if (exponent_less_1023 > 51)
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{
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if (exponent_less_1023 == 1024)
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/* x is NaN or infinite. */
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return x + x;
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else
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return x;
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}
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else
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{
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__uint32_t exponent_mask = 0xffffffff >> (exponent_less_1023 - 20);
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__uint32_t tmp;
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if ((lsw & exponent_mask) == 0)
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/* x is an integral value. */
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return x;
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tmp = lsw + (1 << (51 - exponent_less_1023));
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if (tmp < lsw)
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msw += 1;
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lsw = tmp;
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lsw &= ~exponent_mask;
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}
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INSERT_WORDS(x, msw, lsw);
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return x;
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}
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#endif /* _DOUBLE_IS_32BITS */
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