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 // 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 */ 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
