/*
        Haiku ATI video driver adapted from the X.org ATI driver.

        Copyright 1997 through 2004 by Marc Aurele La France (TSI @ UQV), tsi@xfree86.org

        Copyright 2009 Haiku, Inc.  All rights reserved.
        Distributed under the terms of the MIT license.

        Authors:
        Gerald Zajac 2009
*/

#include "accelerant.h"
#include "mach64.h"


#define MAX_INT ((int)((unsigned int)(-1) >> 2))



void
Mach64_ReduceRatio(int *numerator, int *denominator)
{
        // Reduce a fraction by factoring out the largest common divider of the
        // fraction's numerator and denominator.

        int multiplier = *numerator;
        int divider = *denominator;
        int remainder;

        while ((remainder = multiplier % divider)) {
                multiplier = divider;
                divider = remainder;
        }

        *numerator /= divider;
        *denominator /= divider;
}



int
Mach64_Divide(int numerator, int denominator, int shift, const int roundingKind)
{
        // 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)).

        Mach64_ReduceRatio(&numerator, &denominator);

        // Deal with left shifts but try to keep the denominator even.
        if (denominator & 1) {
                if (denominator <= MAX_INT) {
                        denominator <<= 1;
                        shift++;
                }
        } else {
                while ((shift > 0) && !(denominator & 3)) {
                        denominator >>= 1;
                        shift--;
                }
        }

        // Deal with right shifts.
        while (shift < 0) {
                if ((numerator & 1) && (denominator <= MAX_INT))
                        denominator <<= 1;
                else
                        numerator >>= 1;

                shift++;
        }

        int rounding = 0;                                       // Default to floor

        if (!roundingKind)                                      // nearest
                rounding = denominator >> 1;
        else if (roundingKind > 0)                      // ceiling
                rounding = denominator - 1;

        return ((numerator / denominator) << shift) +
                   ((((numerator % denominator) << shift) + rounding) / denominator);
}