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99 lines
2.5 KiB
C
99 lines
2.5 KiB
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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FUNCTION
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<<trunc>>, <<truncf>>--round to integer, towards zero
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INDEX
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trunc
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INDEX
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truncf
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ANSI_SYNOPSIS
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#include <math.h>
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double trunc(double <[x]>);
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float truncf(float <[x]>);
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DESCRIPTION
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The <<trunc>> functions round their argument to the integer value, in
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floating format, nearest to but no larger in magnitude than the
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argument, regardless of the current rounding direction. (While the
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"inexact" floating-point exception behavior is unspecified by the C
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standard, the <<trunc>> functions are written so that "inexact" is not
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raised if the result does not equal the argument, which behavior is as
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recommended by IEEE 754 for its related functions.)
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RETURNS
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<[x]> truncated to an integral value.
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PORTABILITY
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ANSI C, POSIX
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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 trunc(double x)
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#else
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double trunc(x)
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double x;
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#endif
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{
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int signbit;
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/* Most significant word, least significant word. */
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int msw;
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unsigned int lsw;
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int exponent_less_1023;
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EXTRACT_WORDS(msw, lsw, x);
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/* Extract sign bit. */
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signbit = msw & 0x80000000;
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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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/* All significant digits are in msw. */
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if (exponent_less_1023 < 0)
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{
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/* -1 < x < 1, so result is +0 or -0. */
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INSERT_WORDS(x, signbit, 0);
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}
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else
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{
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/* All relevant fraction bits are in msw, so lsw of the result is 0. */
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INSERT_WORDS(x, signbit | (msw & ~(0x000fffff >> exponent_less_1023)), 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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{
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/* x is infinite, or not a number, so trigger an exception. */
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return x + x;
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}
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/* All bits in the fraction fields of the msw and lsw are needed in the result. */
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}
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else
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{
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/* All fraction bits in msw are relevant. Truncate irrelevant
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bits from lsw. */
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INSERT_WORDS(x, msw, lsw & ~(0xffffffffu >> (exponent_less_1023 - 20)));
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}
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return x;
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}
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#endif /* _DOUBLE_IS_32BITS */
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