1 /*
2 * Copyright 2017 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #ifndef SkBitmapProcState_utils_DEFINED
9 #define SkBitmapProcState_utils_DEFINED
10
11 // Helper to ensure that when we shift down, we do it w/o sign-extension
12 // so the caller doesn't have to manually mask off the top 16 bits
13 //
SK_USHIFT16(unsigned x)14 static inline unsigned SK_USHIFT16(unsigned x) {
15 return x >> 16;
16 }
17
18 /*
19 * The decal_ functions require that
20 * 1. dx > 0
21 * 2. [fx, fx+dx, fx+2dx, fx+3dx, ... fx+(count-1)dx] are all <= maxX
22 *
23 * In addition, we use SkFractionalInt to keep more fractional precision than
24 * just SkFixed, so we will abort the decal_ call if dx is very small, since
25 * the decal_ function just operates on SkFixed. If that were changed, we could
26 * skip the very_small test here.
27 */
can_truncate_to_fixed_for_decal(SkFixed fx,SkFixed dx,int count,unsigned max)28 static inline bool can_truncate_to_fixed_for_decal(SkFixed fx,
29 SkFixed dx,
30 int count, unsigned max) {
31 SkASSERT(count > 0);
32
33 // if decal_ kept SkFractionalInt precision, this would just be dx <= 0
34 // I just made up the 1/256. Just don't want to perceive accumulated error
35 // if we truncate frDx and lose its low bits.
36 if (dx <= SK_Fixed1 / 256) {
37 return false;
38 }
39
40 // Note: it seems the test should be (fx <= max && lastFx <= max); but
41 // historically it's been a strict inequality check, and changing produces
42 // unexpected diffs. Further investigation is needed.
43
44 // We cast to unsigned so we don't have to check for negative values, which
45 // will now appear as very large positive values, and thus fail our test!
46 if ((unsigned)SkFixedFloorToInt(fx) >= max) {
47 return false;
48 }
49
50 // Promote to 64bit (48.16) to avoid overflow.
51 const uint64_t lastFx = fx + sk_64_mul(dx, count - 1);
52
53 return sk_64_isS32(lastFx) && (unsigned)SkFixedFloorToInt(sk_64_asS32(lastFx)) < max;
54 }
55
56 #endif /* #ifndef SkBitmapProcState_utils_DEFINED */
57