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

include/core/SkDataTable.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkDataTable_DEFINED
+#define SkDataTable_DEFINED
+
+#include "SkChunkAlloc.h"
+#include "SkData.h"
+#include "SkFlattenable.h"
+#include "SkString.h"
+#include "SkTDArray.h"
+
+/**
+ *  Like SkData, SkDataTable holds an immutable data buffer. The data buffer is
+ *  organized into a table of entries, each with a length, so the entries are
+ *  not required to all be the same size.
+ */
+class SK_API SkDataTable : public SkFlattenable {
+public:
+    SK_DECLARE_INST_COUNT(SkDataTable)
+
+    /**
+     *  Returns true if the table is empty (i.e. has no entries).
+     */
+    bool isEmpty() const { return 0 == fCount; }
+
+    /**
+     *  Return the number of entries in the table. 0 for an empty table
+     */
+    int count() const { return fCount; }
+
+    /**
+     *  Return the size of the index'th entry in the table. The caller must
+     *  ensure that index is valid for this table.
+     */
+    size_t  atSize(int index) const;
+
+    /**
+     *  Return a pointer to the data of the index'th entry in the table.
+     *  The caller must ensure that index is valid for this table.
+     *
+     *  @param size If non-null, this returns the byte size of this entry. This
+     *              will be the same value that atSize(index) would return.
+     */
+    const void* atData(int index, size_t* size = NULL) const;
+
+    template <typename T>
+    const T* atDataT(int index, size_t* size = NULL) const {
+        return reinterpret_cast<const T*>(this->atData(index, size));
+    }
+
+    /**
+     *  Returns the index'th entry as a c-string, and assumes that the trailing
+     *  null byte had been copied into the table as well.
+     */
+    const char* atStr(int index) const {
+        size_t size;
+        const char* str = this->atDataT<const char>(index, &size);
+        SkASSERT(strlen(str) + 1 == size);
+        return str;
+    }
+
+    /**
+     *  Return a new DataTable that contains a copy of the data stored in each
+     *  "array".
+     *
+     *  @param ptrs array of points to each element to be copied into the table.
+     *  @param sizes array of byte-lengths for each entry in the corresponding
+     *               ptrs[] array.
+     *  @param count the number of array elements in ptrs[] and sizes[] to copy.
+     */
+    static SkDataTable* NewCopyArrays(const void * const * ptrs, const size_t sizes[],
+                                      int count);
+
+    /**
+     *  Return a new table that contains a copy of the data in array.
+     *
+     *  @param array contiguous array of data for all elements to be copied.
+     *  @param elemSize byte-length for a given element.
+     *  @param count the number of entries to be copied out of array. The number
+     *               of bytes that will be copied is count * elemSize.
+     */
+    static SkDataTable* NewCopyArray(const void* array, size_t elemSize,
+                                     int count);
+    
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkDataTable)
+
+protected:
+    SkDataTable(SkFlattenableReadBuffer&);
+    virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
+    
+private:
+    SkDataTable(int count, SkData* dataWeTakeOverOwnership);
+    virtual ~SkDataTable();
+
+    int     fCount;
+    SkData* fData;
+
+    typedef SkFlattenable INHERITED;
+};
+
+/**
+ *  Helper class that allows for incrementally building up the data needed to
+ *  create a SkDataTable.
+ */
+class SK_API SkDataTableBuilder {
+public:
+    SkDataTableBuilder(size_t minChunkSize);
+    ~SkDataTableBuilder();
+
+    int  count() const { return fSizes.count(); }
+
+    /**
+     *  Forget any previously appended entries, setting count() back to 0.
+     */
+    void reset();
+
+    /**
+     *  Copy size-bytes from data, and append it to the growing SkDataTable.
+     */
+    void append(const void* data, size_t size);
+
+    /**
+     *  Helper version of append() passes strlen() + 1 for the size,
+     *  so the trailing-zero will be copied as well.
+     */
+    void appendStr(const char str[]) {
+        this->append(str, strlen(str) + 1);
+    }
+
+    /**
+     *  Helper version of append() passes string.size() + 1 for the size,
+     *  so the trailing-zero will be copied as well.
+     */
+    void appendString(const SkString& string) {
+        this->append(string.c_str(), string.size() + 1);
+    }
+
+    /**
+     *  Return an SkDataTable from the accumulated entries that were added by
+     *  calls to append(). This data is logically distinct from the builder, and
+     *  will not be affected by any subsequent calls to the builder.
+     */
+    SkDataTable* createDataTable();
+
+private:
+    SkTDArray<size_t> fSizes;
+    SkTDArray<void*>  fPtrs;
+    SkChunkAlloc      fHeap;
+};
+
+#endif