atiutil.c revision 32b578d3 
1/*
2 * Copyright 1997 through 2004 by Marc Aurele La France (TSI @ UQV), tsi@xfree86.org
3 *
4 * Permission to use, copy, modify, distribute, and sell this software and its
5 * documentation for any purpose is hereby granted without fee, provided that
6 * the above copyright notice appear in all copies and that both that copyright
7 * notice and this permission notice appear in supporting documentation, and
8 * that the name of Marc Aurele La France not be used in advertising or
9 * publicity pertaining to distribution of the software without specific,
10 * written prior permission.  Marc Aurele La France makes no representations
11 * about the suitability of this software for any purpose.  It is provided
12 * "as-is" without express or implied warranty.
13 *
14 * MARC AURELE LA FRANCE DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
15 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.  IN NO
16 * EVENT SHALL MARC AURELE LA FRANCE BE LIABLE FOR ANY SPECIAL, INDIRECT OR
17 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
18 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
19 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
20 * PERFORMANCE OF THIS SOFTWARE.
21 */
22
23#ifdef HAVE_CONFIG_H
24#include "config.h"
25#endif
26
27#include "atiutil.h"
28
29/*
30 * ATIReduceRatio --
31 *
32 * Reduce a fraction by factoring out the largest common divider of the
33 * fraction's numerator and denominator.
34 */
35void
36ATIReduceRatio
37(
38    int *Numerator,
39    int *Denominator
40)
41{
42    int Multiplier, Divider, Remainder;
43
44    Multiplier = *Numerator;
45    Divider = *Denominator;
46
47    while ((Remainder = Multiplier % Divider))
48    {
49        Multiplier = Divider;
50        Divider = Remainder;
51    }
52
53    *Numerator /= Divider;
54    *Denominator /= Divider;
55}
56
57/*
58 * ATIDivide --
59 *
60 * Using integer arithmetic and avoiding overflows, this function finds the
61 * rounded integer that best approximates
62 *
63 *         Numerator      Shift
64 *        ----------- * 2
65 *        Denominator
66 *
67 * using the specified rounding (floor (<0), nearest (=0) or ceiling (>0)).
68 */
69int
70ATIDivide
71(
72    int       Numerator,
73    int       Denominator,
74    int       Shift,
75    const int RoundingKind
76)
77{
78    int Rounding = 0;                           /* Default to floor */
79
80#define MaxInt ((int)((unsigned int)(-1) >> 2))
81
82    ATIReduceRatio(&Numerator, &Denominator);
83
84    /* Deal with left shifts but try to keep the denominator even */
85    if (Denominator & 1)
86    {
87        if (Denominator <= MaxInt)
88        {
89            Denominator <<= 1;
90            Shift++;
91        }
92    }
93    else while ((Shift > 0) && !(Denominator & 3))
94    {
95        Denominator >>= 1;
96        Shift--;
97    }
98
99    /* Deal with right shifts */
100    while (Shift < 0)
101    {
102        if ((Numerator & 1) && (Denominator <= MaxInt))
103            Denominator <<= 1;
104        else
105            Numerator >>= 1;
106
107        Shift++;
108    }
109
110    if (!RoundingKind)                          /* Nearest */
111        Rounding = Denominator >> 1;
112    else if (RoundingKind > 0)                  /* Ceiling */
113        Rounding = Denominator - 1;
114
115    return ((Numerator / Denominator) << Shift) +
116            ((((Numerator % Denominator) << Shift) + Rounding) / Denominator);
117}
118