1/*
2    Copyright 2011 Google Inc.
3
4    Licensed under the Apache License, Version 2.0 (the "License");
5    you may not use this file except in compliance with the License.
6    You may obtain a copy of the License at
7
8    http://www.apache.org/licenses/LICENSE-2.0
9
10    Unless required by applicable law or agreed to in writing, software
11    distributed under the License is distributed on an "AS IS" BASIS,
12    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13    See the License for the specific language governing permissions and
14    limitations under the License.
15 */
16
17#include "SkClampRange.h"
18
19/*
20 *  returns [0..count] for the number of steps (<= count) for which x0 <= edge
21 *  given each step is followed by x0 += dx
22 */
23static int chop(int64_t x0, SkFixed edge, int64_t x1, int64_t dx, int count) {
24    SkASSERT(dx > 0);
25    SkASSERT(count >= 0);
26
27    if (x0 >= edge) {
28        return 0;
29    }
30    if (x1 <= edge) {
31        return count;
32    }
33    int64_t n = (edge - x0 + dx - 1) / dx;
34    SkASSERT(n >= 0);
35    SkASSERT(n <= count);
36    return (int)n;
37}
38
39static bool overflows_fixed(int64_t x) {
40    return x < -SK_FixedMax || x > SK_FixedMax;
41}
42
43void SkClampRange::initFor1(SkFixed fx) {
44    fCount0 = fCount1 = fCount2 = 0;
45    if (fx <= 0) {
46        fCount0 = 1;
47    } else if (fx < 0xFFFF) {
48        fCount1 = 1;
49        fFx1 = fx;
50    } else {
51        fCount2 = 1;
52    }
53}
54
55void SkClampRange::init(SkFixed fx0, SkFixed dx0, int count, int v0, int v1) {
56    SkASSERT(count > 0);
57
58    fV0 = v0;
59    fV1 = v1;
60    fOverflowed = false;
61
62    // special case 1 == count, as it is slightly common for skia
63    // and avoids us ever calling divide or 64bit multiply
64    if (1 == count) {
65        this->initFor1(fx0);
66        return;
67    }
68
69    int64_t fx = fx0;
70    int64_t dx = dx0;
71    // start with ex equal to the last computed value
72    int64_t ex = fx + (count - 1) * dx;
73    fOverflowed = overflows_fixed(ex);
74
75    if ((uint64_t)(fx | ex) <= 0xFFFF) {
76        fCount0 = fCount2 = 0;
77        fCount1 = count;
78        fFx1 = fx0;
79        return;
80    }
81    if (fx <= 0 && ex <= 0) {
82        fCount1 = fCount2 = 0;
83        fCount0 = count;
84        return;
85    }
86    if (fx >= 0xFFFF && ex >= 0xFFFF) {
87        fCount0 = fCount1 = 0;
88        fCount2 = count;
89        return;
90    }
91
92    int extraCount = 0;
93
94    // now make ex be 1 past the last computed value
95    ex += dx;
96    fOverflowed = overflows_fixed(ex);
97    // now check for over/under flow
98    if (fOverflowed) {
99        int originalCount = count;
100        int64_t ccount;
101        bool swap = dx < 0;
102        if (swap) {
103            dx = -dx;
104            fx = -fx;
105        }
106        ccount = (SK_FixedMax - fx + dx - 1) / dx;
107        if (swap) {
108            dx = -dx;
109            fx = -fx;
110        }
111        SkASSERT(ccount > 0 && ccount <= SK_FixedMax);
112
113        count = (int)ccount;
114        if (0 == count) {
115            this->initFor1(fx0);
116            if (dx > 0) {
117                fCount2 += originalCount - 1;
118            } else {
119                fCount0 += originalCount - 1;
120            }
121            return;
122        }
123        extraCount = originalCount - count;
124        ex = fx + dx * count;
125    }
126
127    bool doSwap = dx < 0;
128
129    if (doSwap) {
130        ex -= dx;
131        fx -= dx;
132        SkTSwap(fx, ex);
133        dx = -dx;
134    }
135
136
137    fCount0 = chop(fx, 0, ex, dx, count);
138    count -= fCount0;
139    fx += fCount0 * dx;
140    SkASSERT(fx >= 0);
141    SkASSERT(fCount0 == 0 || (fx - dx) < 0);
142    fCount1 = chop(fx, 0xFFFF, ex, dx, count);
143    count -= fCount1;
144    fCount2 = count;
145
146#ifdef SK_DEBUG
147    fx += fCount1 * dx;
148    SkASSERT(fx <= ex);
149    if (fCount2 > 0) {
150        SkASSERT(fx >= 0xFFFF);
151        if (fCount1 > 0) {
152            SkASSERT(fx - dx < 0xFFFF);
153        }
154    }
155#endif
156
157    if (doSwap) {
158        SkTSwap(fCount0, fCount2);
159        SkTSwap(fV0, fV1);
160        dx = -dx;
161    }
162
163    if (fCount1 > 0) {
164        fFx1 = fx0 + fCount0 * (int)dx;
165    }
166
167    if (dx > 0) {
168        fCount2 += extraCount;
169    } else {
170        fCount0 += extraCount;
171    }
172}
173
174