speedup peek32() when the offset is in the last block (fTail)
Review URL: https://codereview.appspot.com/6906047
git-svn-id: http://skia.googlecode.com/svn/trunk@6708 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/include/core/SkWriter32.h b/include/core/SkWriter32.h
index 9354d6d..3b9bdfc 100644
--- a/include/core/SkWriter32.h
+++ b/include/core/SkWriter32.h
@@ -37,6 +37,7 @@
fSize(0),
fSingleBlock(NULL),
fSingleBlockSize(0),
+ fWrittenBeforeLastBlock(0),
fHead(NULL),
fTail(NULL),
fHeadIsExternalStorage(false) {}
@@ -197,6 +198,9 @@
char* fSingleBlock;
uint32_t fSingleBlockSize;
+ // sum of bytes written in all blocks *before* fTail
+ uint32_t fWrittenBeforeLastBlock;
+
struct Block;
Block* fHead;
Block* fTail;
diff --git a/src/core/SkWriter32.cpp b/src/core/SkWriter32.cpp
index 6a84927..ce240c2 100644
--- a/src/core/SkWriter32.cpp
+++ b/src/core/SkWriter32.cpp
@@ -66,6 +66,7 @@
fSize = 0;
fSingleBlock = NULL;
fSingleBlockSize = 0;
+ fWrittenBeforeLastBlock = 0;
storageSize &= ~3; // trunc down to multiple of 4
if (storageSize >= MIN_BLOCKSIZE) {
@@ -96,6 +97,7 @@
}
fSize = 0;
+ fWrittenBeforeLastBlock = 0;
fSingleBlock = NULL;
if (fHeadIsExternalStorage) {
SkASSERT(fHead);
@@ -128,7 +130,11 @@
if (NULL == block) {
SkASSERT(NULL == fHead);
fHead = fTail = block = Block::Create(SkMax32(size, fMinSize));
+ SkASSERT(0 == fWrittenBeforeLastBlock);
} else if (block->available() < size) {
+ SkASSERT(fSize > 0);
+ fWrittenBeforeLastBlock = fSize;
+
fTail = Block::Create(SkMax32(size, fMinSize));
block->fNext = fTail;
block = fTail;
@@ -149,6 +155,11 @@
return (uint32_t*)(fSingleBlock + offset);
}
+ // try the fast case, where offset is within fTail
+ if (offset >= fWrittenBeforeLastBlock) {
+ return fTail->peek32(offset - fWrittenBeforeLastBlock);
+ }
+
Block* block = fHead;
SkASSERT(NULL != block);
@@ -179,29 +190,39 @@
return;
}
- // Similar to peek32, except that we free up any following blocks
- Block* block = fHead;
- SkASSERT(NULL != block);
- while (offset >= block->fAllocatedSoFar) {
- offset -= block->fAllocatedSoFar;
- block = block->fNext;
+ // Try the fast case, where offset is within fTail
+ if (offset >= fWrittenBeforeLastBlock) {
+ fTail->fAllocatedSoFar = offset - fWrittenBeforeLastBlock;
+ } else {
+ // Similar to peek32, except that we free up any following blocks.
+ // We have to re-compute fWrittenBeforeLastBlock as well.
+
+ size_t globalOffset = offset;
+ Block* block = fHead;
SkASSERT(NULL != block);
- }
+ while (offset >= block->fAllocatedSoFar) {
+ offset -= block->fAllocatedSoFar;
+ block = block->fNext;
+ SkASSERT(NULL != block);
+ }
- // update the size on the "last" block
- block->fAllocatedSoFar = offset;
- // end our list
- fTail = block;
- Block* next = block->fNext;
- block->fNext = NULL;
- // free up any trailing blocks
- block = next;
- while (block) {
+ // this has to be recomputed, since we may free up fTail
+ fWrittenBeforeLastBlock = globalOffset - offset;
+
+ // update the size on the "last" block
+ block->fAllocatedSoFar = offset;
+ // end our list
+ fTail = block;
Block* next = block->fNext;
- sk_free(block);
+ block->fNext = NULL;
+ // free up any trailing blocks
block = next;
+ while (block) {
+ Block* next = block->fNext;
+ sk_free(block);
+ block = next;
+ }
}
-
SkDEBUGCODE(this->validate();)
}
@@ -310,6 +331,10 @@
SkASSERT(SkIsAlign4(block->fSizeOfBlock));
SkASSERT(SkIsAlign4(block->fAllocatedSoFar));
SkASSERT(block->fAllocatedSoFar <= block->fSizeOfBlock);
+ if (NULL == block->fNext) {
+ SkASSERT(fTail == block);
+ SkASSERT(fWrittenBeforeLastBlock == accum);
+ }
accum += block->fAllocatedSoFar;
SkASSERT(accum <= fSize);
block = block->fNext;