add SkDataTable, to efficiently store an immutable array. Includes a builder

src/core/SkDataTable.cpp

Index: src/core/SkDataTable.cpp
===================================================================
--- src/core/SkDataTable.cpp	(revision 0)
+++ src/core/SkDataTable.cpp	(revision 0)
@@ -0,0 +1,135 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkData.h"
+#include "SkDataTable.h"
+#include "SkFlattenableBuffers.h"
+
+SK_DEFINE_INST_COUNT(SkDataTable)
+
+SkDataTable::SkDataTable(int count, SkData* data)
+    : fCount(count)
+    , fData(data) {}
+
+SkDataTable::~SkDataTable() {
+    fData->unref();
+}
+
+struct ElemHead {
+    const void* fPtr;
+    uintptr_t   fSize;
+
+    static const ElemHead* Get(SkData* data) {
+        return (const ElemHead*)(data->data());
+    }
+};
+
+size_t SkDataTable::atSize(int index) const {
+    SkASSERT((unsigned)index < (unsigned)fCount);
+    return ElemHead::Get(fData)[index].fSize;
+}
+
+const void* SkDataTable::atData(int index, size_t* size) const {
+    SkASSERT((unsigned)index < (unsigned)fCount);
+    const ElemHead& head = ElemHead::Get(fData)[index];
+    if (size) {
+        *size = head.fSize;
+    }
+    return head.fPtr;
+}
+
+SkDataTable::SkDataTable(SkFlattenableReadBuffer& buffer) : INHERITED(buffer) {
+    fCount = buffer.read32();
+    fData = buffer.readFlattenableT<SkData>();
+}
+
+void SkDataTable::flatten(SkFlattenableWriteBuffer& buffer) const {
+    this->INHERITED::flatten(buffer);
+    buffer.write32(fCount);
+    buffer.writeFlattenable(fData);
+}
+
+SkDataTable* SkDataTable::NewCopyArrays(const void * const * ptrs,
+                                        const size_t sizes[], int count) {
+    if (count < 0) {
+        count = 0;
+    }
+
+    size_t headerSize = count * sizeof(ElemHead);
+    size_t dataSize = 0;
+    for (int i = 0; i < count; ++i) {
+        dataSize += sizes[i];
+    }
+
+    size_t bufferSize = headerSize + dataSize;
+    void* buffer = sk_malloc_throw(bufferSize);
+
+    ElemHead* headerCurr = (ElemHead*)buffer;
+    char* dataCurr = (char*)buffer + headerSize;
+    for (int i = 0; i < count; ++i) {
+        headerCurr[i].fPtr = dataCurr;
+        headerCurr[i].fSize = sizes[i];
+        memcpy(dataCurr, ptrs[i], sizes[i]);
+        dataCurr += sizes[i];
+    }
+
+    return SkNEW_ARGS(SkDataTable, (count,
+                                    SkData::NewFromMalloc(buffer, bufferSize)));
+}
+
+SkDataTable* SkDataTable::NewCopyArray(const void* array, size_t elemSize,
+                                       int count) {
+    if (count < 0) {
+        count = 0;
+    }
+    
+    size_t headerSize = count * sizeof(ElemHead);
+    size_t dataSize = count * elemSize;
+    
+    size_t bufferSize = headerSize + dataSize;
+    void* buffer = sk_malloc_throw(bufferSize);
+    
+    ElemHead* headerCurr = (ElemHead*)buffer;
+    char* dataCurr = (char*)buffer + headerSize;
+    for (int i = 0; i < count; ++i) {
+        headerCurr[i].fPtr = dataCurr;
+        headerCurr[i].fSize = elemSize;
+        dataCurr += elemSize;
+    }
+    memcpy((char*)buffer + headerSize, array, dataSize);
+    
+    return SkNEW_ARGS(SkDataTable, (count,
+                                    SkData::NewFromMalloc(buffer, bufferSize)));
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+SkDataTableBuilder::SkDataTableBuilder(size_t minChunkSize)
+    : fHeap(minChunkSize) {}
+
+SkDataTableBuilder::~SkDataTableBuilder() {}
+
+void SkDataTableBuilder::reset() {
+    fSizes.reset();
+    fPtrs.reset();
+    fHeap.reset();
+}
+
+void SkDataTableBuilder::append(const void* src, size_t size) {
+    void* dst = fHeap.alloc(size, SkChunkAlloc::kThrow_AllocFailType);
+    memcpy(dst, src, size);
+
+    *fSizes.append() = size;
+    *fPtrs.append() = dst;
+}
+
+SkDataTable* SkDataTableBuilder::createDataTable() {
+    SkASSERT(fSizes.count() == fPtrs.count());
+    return SkDataTable::NewCopyArrays(fPtrs.begin(), fSizes.begin(),
+                                      fSizes.count());
+}
+