71 lines
1.0 KiB
C
71 lines
1.0 KiB
C
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/* round.c
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*
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* Round double to nearest or even integer valued double
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*
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*
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*
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* SYNOPSIS:
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*
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* double x, y, round();
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*
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* y = round(x);
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*
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*
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*
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* DESCRIPTION:
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*
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* Returns the nearest integer to x as a double precision
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* floating point result. If x ends in 0.5 exactly, the
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* nearest even integer is chosen.
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*
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*
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*
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* ACCURACY:
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*
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* If x is greater than 1/(2*MACHEP), its closest machine
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* representation is already an integer, so rounding does
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* not change it.
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*/
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/*
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Cephes Math Library Release 2.1: January, 1989
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Copyright 1984, 1987, 1989 by Stephen L. Moshier
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Direct inquiries to 30 Frost Street, Cambridge, MA 02140
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*/
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#include "mconf.h"
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#ifdef ANSIPROT
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double floor ( double );
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#else
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double floor();
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#endif
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double round(x)
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double x;
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{
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double y, r;
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/* Largest integer <= x */
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y = floor(x);
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/* Fractional part */
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r = x - y;
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/* Round up to nearest. */
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if( r > 0.5 )
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goto rndup;
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/* Round to even */
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if( r == 0.5 )
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{
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r = y - 2.0 * floor( 0.5 * y );
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if( r == 1.0 )
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{
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rndup:
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y += 1.0;
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}
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}
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/* Else round down. */
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return(y);
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}
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