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/* $XFree86: xc/programs/Xserver/hw/xfree86/drivers/ati/atiutil.c,v 1.8 2003/01/01 19:16:34 tsi Exp $ */
/*
* Copyright 1997 through 2004 by Marc Aurele La France (TSI @ UQV), tsi@xfree86.org
*
* Permission to use, copy, modify, distribute, and sell this software and its
* documentation for any purpose is hereby granted without fee, provided that
* the above copyright notice appear in all copies and that both that copyright
* notice and this permission notice appear in supporting documentation, and
* that the name of Marc Aurele La France not be used in advertising or
* publicity pertaining to distribution of the software without specific,
* written prior permission. Marc Aurele La France makes no representations
* about the suitability of this software for any purpose. It is provided
* "as-is" without express or implied warranty.
*
* MARC AURELE LA FRANCE DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
* INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
* EVENT SHALL MARC AURELE LA FRANCE BE LIABLE FOR ANY SPECIAL, INDIRECT OR
* CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
* DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
* TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
#include "atiutil.h"
/*
* ATIReduceRatio --
*
* Reduce a fraction by factoring out the largest common divider of the
* fraction's numerator and denominator.
*/
void
ATIReduceRatio
(
int *Numerator,
int *Denominator
)
{
int Multiplier, Divider, Remainder;
Multiplier = *Numerator;
Divider = *Denominator;
while ((Remainder = Multiplier % Divider))
{
Multiplier = Divider;
Divider = Remainder;
}
*Numerator /= Divider;
*Denominator /= Divider;
}
/*
* ATIDivide --
*
* Using integer arithmetic and avoiding overflows, this function finds the
* rounded integer that best approximates
*
* Numerator Shift
* ----------- * 2
* Denominator
*
* using the specified rounding (floor (<0), nearest (=0) or ceiling (>0)).
*/
int
ATIDivide
(
int Numerator,
int Denominator,
int Shift,
const int RoundingKind
)
{
int Rounding = 0; /* Default to floor */
#define MaxInt ((int)((unsigned int)(-1) >> 2))
ATIReduceRatio(&Numerator, &Denominator);
/* Deal with left shifts but try to keep the denominator even */
if (Denominator & 1)
{
if (Denominator <= MaxInt)
{
Denominator <<= 1;
Shift++;
}
}
else while ((Shift > 0) && !(Denominator & 3))
{
Denominator >>= 1;
Shift--;
}
/* Deal with right shifts */
while (Shift < 0)
{
if ((Numerator & 1) && (Denominator <= MaxInt))
Denominator <<= 1;
else
Numerator >>= 1;
Shift++;
}
if (!RoundingKind) /* Nearest */
Rounding = Denominator >> 1;
else if (RoundingKind > 0) /* Ceiling */
Rounding = Denominator - 1;
return ((Numerator / Denominator) << Shift) +
((((Numerator % Denominator) << Shift) + Rounding) / Denominator);
}
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