Have peek32 return uint32_t& to make it harder to look at more than 4 bytes.

BUG=skia:
R=reed@google.com, robertphillips@google.com

Author: mtklein@google.com

Review URL: https://codereview.chromium.org/145053003

git-svn-id: http://skia.googlecode.com/svn/trunk@13265 2bbb7eff-a529-9590-31e7-b0007b416f81

4 files changed, 34 insertions, 38 deletions

diff --git a/include/core/SkWriter32.h b/include/core/SkWriter32.h
index 6bb59c5dbc..b193cbe7c4 100644
--- a/include/core/SkWriter32.h
+++ b/include/core/SkWriter32.h
@@ -79,19 +79,9 @@ public:
         return p;
     }
 
-    // return the address of the 4byte int at the specified offset (which must
-    // be a multiple of 4. This does not allocate any new space, so the returned
-    // address is only valid for 1 int.
-    uint32_t* peek32(size_t offset) {
-        SkASSERT(SkAlign4(offset) == offset);
-        const int count = SkToInt(offset/4);
-        SkASSERT(count < fCount);
-
-        if (count < this->externalCount()) {
-            return fExternal + count;
-        }
-        return &fInternal[count - this->externalCount()];
-    }
+    // Read or write 4 bytes at offset, which must be a multiple of 4 <= size().
+    uint32_t read32At(size_t offset) { return this->atOffset(offset); }
+    void write32At(size_t offset, uint32_t val) { this->atOffset(offset) = val; }
 
     bool writeBool(bool value) {
         this->write32(value);
@@ -215,8 +205,7 @@ public:
 
     /**
      *  Move the cursor back to offset bytes from the beginning.
-     *  This has the same restrictions as peek32: offset must be <= size() and
-     *  offset must be a multiple of 4.
+     *  offset must be a multiple of 4 no greater than size().
      */
     void rewindToOffset(size_t offset) {
         SkASSERT(SkAlign4(offset) == offset);
@@ -249,6 +238,18 @@ public:
     }
 
 private:
+    uint32_t& atOffset(size_t offset) {
+        SkASSERT(SkAlign4(offset) == offset);
+        const int count = SkToInt(offset/4);
+        SkASSERT(count < fCount);
+
+        if (count < this->externalCount()) {
+            return fExternal[count];
+        }
+        return fInternal[count - this->externalCount()];
+    }
+
+
     // Number of uint32_t written into fExternal.  <= fExternalLimit.
     int externalCount() const { return fCount - fInternal.count(); }
 
diff --git a/src/core/SkPictureRecord.cpp b/src/core/SkPictureRecord.cpp
index b2f9216df6..4279ac3c2c 100644
--- a/src/core/SkPictureRecord.cpp
+++ b/src/core/SkPictureRecord.cpp
@@ -197,13 +197,13 @@ bool SkPictureRecord::isDrawingToLayer() const {
  * Read the op code from 'offset' in 'writer' and extract the size too.
  */
 static DrawType peek_op_and_size(SkWriter32* writer, int32_t offset, uint32_t* size) {
-    uint32_t* peek = writer->peek32(offset);
+    uint32_t peek = writer->read32At(offset);
 
     uint32_t op;
-    UNPACK_8_24(*peek, op, *size);
+    UNPACK_8_24(peek, op, *size);
     if (MASK_24 == *size) {
         // size required its own slot right after the op code
-        *size = *writer->peek32(offset+kUInt32Size);
+        *size = writer->read32At(offset+kUInt32Size);
     }
     return (DrawType) op;
 }
@@ -306,7 +306,7 @@ static bool remove_save_layer1(SkWriter32* writer, int32_t offset,
     // back up to the save block
     // TODO: add a stack to track save*/restore offsets rather than searching backwards
     while (offset > 0) {
-        offset = *writer->peek32(offset);
+        offset = writer->read32At(offset);
     }
 
     int pattern[] = { SAVE_LAYER, kDRAW_BITMAP_FLAVOR, /* RESTORE */ };
@@ -331,8 +331,8 @@ static bool remove_save_layer1(SkWriter32* writer, int32_t offset,
  * field alone so the NOOP can be skipped later.
  */
 static void convert_command_to_noop(SkWriter32* writer, uint32_t offset) {
-    uint32_t* ptr = writer->peek32(offset);
-    *ptr = (*ptr & MASK_24) | (NOOP << 24);
+    uint32_t command = writer->read32At(offset);
+    writer->write32At(offset, (command & MASK_24) | (NOOP << 24));
 }
 
 /*
@@ -353,8 +353,8 @@ static bool merge_savelayer_paint_into_drawbitmp(SkWriter32* writer,
     uint32_t slPaintOffset = getPaintOffset(SAVE_LAYER, saveLayerInfo.fSize);
 
     // we have a match, now we need to get the paints involved
-    uint32_t dbmPaintId = *writer->peek32(dbmInfo.fOffset+dbmPaintOffset);
-    uint32_t saveLayerPaintId = *writer->peek32(saveLayerInfo.fOffset+slPaintOffset);
+    uint32_t dbmPaintId = writer->read32At(dbmInfo.fOffset+dbmPaintOffset);
+    uint32_t saveLayerPaintId = writer->read32At(saveLayerInfo.fOffset+slPaintOffset);
 
     if (0 == saveLayerPaintId) {
         // In this case the saveLayer/restore isn't needed at all - just kill the saveLayer
@@ -367,9 +367,7 @@ static bool merge_savelayer_paint_into_drawbitmp(SkWriter32* writer,
         // In this case just make the DBM* use the saveLayer's paint, kill the saveLayer
         // and signal the caller (by returning true) to not add the RESTORE op
         convert_command_to_noop(writer, saveLayerInfo.fOffset);
-        uint32_t* ptr = writer->peek32(dbmInfo.fOffset+dbmPaintOffset);
-        SkASSERT(0 == *ptr);
-        *ptr = saveLayerPaintId;
+        writer->write32At(dbmInfo.fOffset+dbmPaintOffset, saveLayerPaintId);
         return true;
     }
 
@@ -402,9 +400,7 @@ static bool merge_savelayer_paint_into_drawbitmp(SkWriter32* writer,
 
     // kill the saveLayer and alter the DBMR2R's paint to be the modified one
     convert_command_to_noop(writer, saveLayerInfo.fOffset);
-    uint32_t* ptr = writer->peek32(dbmInfo.fOffset+dbmPaintOffset);
-    SkASSERT(dbmPaintId == *ptr);
-    *ptr = data->index();
+    writer->write32At(dbmInfo.fOffset+dbmPaintOffset, data->index());
     return true;
 }
 
@@ -425,7 +421,7 @@ static bool remove_save_layer2(SkWriter32* writer, int32_t offset,
     // back up to the save block
     // TODO: add a stack to track save*/restore offsets rather than searching backwards
     while (offset > 0) {
-        offset = *writer->peek32(offset);
+        offset = writer->read32At(offset);
     }
 
     int pattern[] = { SAVE_LAYER, SAVE, CLIP_RECT, kDRAW_BITMAP_FLAVOR, RESTORE, /* RESTORE */ };
@@ -462,7 +458,7 @@ static bool collapse_save_clip_restore(SkWriter32* writer, int32_t offset,
 
     // back up to the save block
     while (offset > 0) {
-        offset = *writer->peek32(offset);
+        offset = writer->read32At(offset);
     }
 
     // now offset points to a save
@@ -477,7 +473,7 @@ static bool collapse_save_clip_restore(SkWriter32* writer, int32_t offset,
     SkASSERT(kSaveSize == opSize);
 
     // get the save flag (last 4-bytes of the space allocated for the opSize)
-    SkCanvas::SaveFlags saveFlags = (SkCanvas::SaveFlags) *writer->peek32(offset+4);
+    SkCanvas::SaveFlags saveFlags = (SkCanvas::SaveFlags) writer->read32At(offset+4);
     if (SkCanvas::kMatrixClip_SaveFlag != saveFlags) {
         // This function's optimization is only correct for kMatrixClip style saves.
         // TODO: set checkMatrix & checkClip booleans here and then check for the
@@ -694,9 +690,9 @@ static bool regionOpExpands(SkRegion::Op op) {
 void SkPictureRecord::fillRestoreOffsetPlaceholdersForCurrentStackLevel(uint32_t restoreOffset) {
     int32_t offset = fRestoreOffsetStack.top();
     while (offset > 0) {
-        uint32_t* peek = fWriter.peek32(offset);
-        offset = *peek;
-        *peek = restoreOffset;
+        uint32_t peek = fWriter.read32At(offset);
+        fWriter.write32At(offset, restoreOffset);
+        offset = peek;
     }
 
 #ifdef SK_DEBUG
diff --git a/src/core/SkWriteBuffer.cpp b/src/core/SkWriteBuffer.cpp
index a295a8c88c..07e8252ed8 100644
--- a/src/core/SkWriteBuffer.cpp
+++ b/src/core/SkWriteBuffer.cpp
@@ -321,5 +321,5 @@ void SkWriteBuffer::writeFlattenable(const SkFlattenable* flattenable) {
     flattenable->flatten(*this);
     uint32_t objSize = fWriter.bytesWritten() - offset;
     // record the obj's size
-    *fWriter.peek32(offset - sizeof(uint32_t)) = objSize;
+    fWriter.write32At(offset - sizeof(uint32_t), objSize);
 }
diff --git a/tests/Writer32Test.cpp b/tests/Writer32Test.cpp
index fa024baffd..2f8b5c6edf 100644
--- a/tests/Writer32Test.cpp
+++ b/tests/Writer32Test.cpp
@@ -102,8 +102,7 @@ static void test1(skiatest::Reporter* reporter, SkWriter32* writer) {
     for (size_t i = 0; i < SK_ARRAY_COUNT(data); ++i) {
         REPORTER_ASSERT(reporter, i*4 == writer->bytesWritten());
         writer->write32(data[i]);
-        uint32_t* addr = writer->peek32(i * 4);
-        REPORTER_ASSERT(reporter, data[i] == *addr);
+        REPORTER_ASSERT(reporter, data[i] == writer->read32At(i*4));
     }
 
     char buffer[sizeof(data)];