Make SkSHA1 and SkM5 use common SkDigestHash result type

src/utils/SkBitmapHasher.cpp

Index: src/utils/SkBitmapHasher.cpp
===================================================================
--- src/utils/SkBitmapHasher.cpp	(revision 8685)
+++ src/utils/SkBitmapHasher.cpp	(working copy)
@@ -11,20 +11,50 @@
 #include "SkBitmapTransformer.h"
 #include "SkCityHash.h"
 #include "SkEndian.h"
+#include "SkMD5.h"
 
 /**
- * Write an integer value into a bytebuffer in little-endian order.
+ * Write an int32_t value into a bytebuffer in little-endian order.
  */
-static void write_int_to_buffer(int val, char* buf) {
-    val = SkEndian_SwapLE32(val);
+static void write_int32_to_buffer(int32_t val, char* buf) {
     for (int byte=0; byte<4; byte++) {
         *buf++ = (char)(val & 0xff);
         val = val >> 8;
     }
 }
 
+#ifdef BITMAP_HASH_TYPE_SkHashDigest
 /*static*/ bool SkBitmapHasher::ComputeDigestInternal(
-        const SkBitmap& bitmap, const SkBitmapTransformer& transformer, SkHashDigest *result) {
+        const SkBitmap& bitmap, const SkBitmapTransformer& transformer, BITMAP_HASH_TYPE *result) {
+    SkMD5 hasher;
+
+    // Start with x/y dimensions.
+    uint8_t dimensions[8];
+    char *bufPtr = reinterpret_cast<char *>(dimensions);
+    write_int32_to_buffer(bitmap.width(), bufPtr);
+    write_int32_to_buffer(bitmap.height(), bufPtr + 4);
+    hasher.update(dimensions, sizeof(dimensions));
+
+    // Add all the pixel data, one transformed row at a time.

[epoger, 2013/04/21 10:54:57]

Patchset 12: when generating an MD5 digest, call hasher.update() with one row of
pixels at a time.


Basically, instead of:

buffer = malloc(entire_bitmap_size)
transformer.copyBitmapToPixelBuffer(buffer)
hasher.update(buffer)

This now does:

buffer = malloc(one_row)
for (each row) {
  transformer.copyRowToPixelBuffer(buffer)
  hasher.update(buffer)
}


It still copies/transforms all pixels of the bitmap (which we have to do in
order to rearrange bits within the pixel representation), but at least now it
doesn't have to malloc a giant buffer (which I would think could be more of a
strain on constrained platforms).

+    size_t rowBufferSize = transformer.bytesNeededPerRow();
+    SkAutoMalloc bufferManager(rowBufferSize);
+    char *buffer = static_cast<char *>(bufferManager.get());
+    for (int row = 0; row < transformer.numRows(); row++) {
+        if (!transformer.copyRowToPixelBuffer(row, buffer, rowBufferSize)) {

[epoger, 2013/04/21 10:54:57]

Ah, now I better see the value of Ben's 
https://codereview.chromium.org/14267031/ ('ARGB image encoder for checksums.') 
That would make this part of the code cleaner.

[bungeman-skia, 2013/04/22 05:14:02]

More importantly (I think), it pulls the bitmap lock/unlock cleanly out of this
loop.

+            return false;
+        }
+        hasher.update(reinterpret_cast<const uint8_t*>(buffer), rowBufferSize);
+    }
+
+    SkMD5::Digest digest;
+    hasher.finish(digest);
+    // EPOGER: instead of creating the extra copy on the stack and running copyFrom, use malloc and then just make the SkHashDigest hold a reference to it?
+    result->copyFrom(&digest, sizeof(digest));
+    return true;
+}
+#else
+/*static*/ bool SkBitmapHasher::ComputeDigestInternal(
+        const SkBitmap& bitmap, const SkBitmapTransformer& transformer, BITMAP_HASH_TYPE *result) {
     size_t pixelBufferSize = transformer.bytesNeededTotal();
     size_t totalBufferSize = pixelBufferSize + 8; // leave room for x/y dimensions
 
@@ -32,9 +62,9 @@
     char *bufferStart = static_cast<char *>(bufferManager.get());
     char *bufPtr = bufferStart;
     // start with the x/y dimensions
-    write_int_to_buffer(bitmap.width(), bufPtr);
+    write_int32_to_buffer(bitmap.width(), bufPtr);
     bufPtr += 4;
-    write_int_to_buffer(bitmap.height(), bufPtr);
+    write_int32_to_buffer(bitmap.height(), bufPtr);
     bufPtr += 4;
 
     // add all the pixel data
@@ -44,8 +74,9 @@
     *result = SkCityHash::Compute64(bufferStart, totalBufferSize);
     return true;
 }
+#endif
 
-/*static*/ bool SkBitmapHasher::ComputeDigest(const SkBitmap& bitmap, SkHashDigest *result) {
+/*static*/ bool SkBitmapHasher::ComputeDigest(const SkBitmap& bitmap, BITMAP_HASH_TYPE *result) {
     const SkBitmapTransformer::PixelFormat kPixelFormat =
         SkBitmapTransformer::kARGB_8888_Premul_PixelFormat;