add helper to check for overflow

pre-CL to aid in changing the convention for when we overflow

Bug: skia:
Change-Id: I1e34a18fefb80187787a1c0c8ed7ee3516744d24
Reviewed-on: https://skia-review.googlesource.com/57103
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>

include/core/SkImageInfo.h

@@ -332,6 +332,11 @@ public:
         return this->computeByteSize(this->minRowBytes());
     }
 
+    // Returns true if the result of computeByteSize (or computeMinByteSize) overflowed
+    static bool ByteSizeOverflowed(size_t byteSize) {
+        return 0 == byteSize;
+    }
+
     bool validRowBytes(size_t rowBytes) const {
         uint64_t minRB = sk_64_mul(fWidth, this->bytesPerPixel());
         return rowBytes >= minRB;

src/core/SkAutoPixmapStorage.cpp

@@ -37,7 +37,7 @@ bool SkAutoPixmapStorage::tryAlloc(const SkImageInfo& info) {
 
     size_t rb;
     size_t size = AllocSize(info, &rb);
-    if (0 == size) {
+    if (SkImageInfo::ByteSizeOverflowed(size)) {
         return false;
     }
     void* pixels = sk_malloc_flags(size, 0);

src/core/SkBitmapCache.cpp

@@ -290,7 +290,7 @@ SkBitmapCache::RecPtr SkBitmapCache::Alloc(const SkBitmapCacheDesc& desc, const
 
     const size_t rb = info.minRowBytes();
     size_t size = info.computeByteSize(rb);
-    if (0 == size) {
+    if (SkImageInfo::ByteSizeOverflowed(size)) {
         return nullptr;
     }
 

src/core/SkMallocPixelRef.cpp

@@ -80,8 +80,8 @@ sk_sp<SkPixelRef> SkMallocPixelRef::MakeUsing(void*(*allocProc)(size_t),
     size_t size = 0;
     if (!info.isEmpty() && rowBytes) {
         size = info.computeByteSize(rowBytes);
-        if (!size) {
-            return nullptr; // overflow
+        if (SkImageInfo::ByteSizeOverflowed(size)) {
+            return nullptr;
         }
     }
 #endif

src/image/SkImage.cpp

@@ -423,7 +423,7 @@ sk_sp<SkImage> SkImageMakeRasterCopyAndAssignColorSpace(const SkImage* src,
 
     size_t rowBytes = info.minRowBytes();
     size_t size = info.computeByteSize(rowBytes);
-    if (size == 0) {
+    if (SkImageInfo::ByteSizeOverflowed(size)) {
         return nullptr;
     }
     auto data = SkData::MakeUninitialized(size);

src/image/SkImage_Raster.cpp

@@ -62,7 +62,7 @@ public:
         }
 
         size_t size = info.computeByteSize(rowBytes);
-        if (0 == size) {
+        if (SkImageInfo::ByteSizeOverflowed(size)) {
             return false;
         }