1 files changed, 115 insertions, 0 deletions
diff --git a/js/src/vm/Compression.h b/js/src/vm/Compression.h
new file mode 100644
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--- /dev/null
+++ b/js/src/vm/Compression.h
@@ -0,0 +1,115 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef vm_Compression_h
+#define vm_Compression_h
+
+#include <zlib.h>
+
+#include "jstypes.h"
+
+#include "js/AllocPolicy.h"
+#include "js/Vector.h"
+
+namespace js {
+
+struct CompressedDataHeader {
+  uint32_t compressedBytes;
+};
+
+class Compressor {
+ public:
+  // After compressing CHUNK_SIZE bytes, we will do a full flush so we can
+  // start decompression at that point.
+  static constexpr size_t CHUNK_SIZE = 64 * 1024;
+
+ private:
+  // Number of bytes we should hand to zlib each compressMore() call.
+  static constexpr size_t MAX_INPUT_SIZE = 2 * 1024;
+
+  z_stream zs;
+  const unsigned char* inp;
+  size_t inplen;
+  size_t outbytes;
+  bool initialized;
+  bool finished;
+
+  // The number of uncompressed bytes written for the current chunk. When this
+  // reaches CHUNK_SIZE, we finish the current chunk and start a new chunk.
+  uint32_t currentChunkSize;
+
+  // At the end of each chunk (and the end of the uncompressed data if it's
+  // not a chunk boundary), we record the offset in the compressed data.
+  js::Vector<uint32_t, 8, SystemAllocPolicy> chunkOffsets;
+
+ public:
+  enum Status { MOREOUTPUT, DONE, CONTINUE, OOM };
+
+  Compressor(const unsigned char* inp, size_t inplen);
+  ~Compressor();
+  bool init();
+  void setOutput(unsigned char* out, size_t outlen);
+  /* Compress some of the input. Return true if it should be called again. */
+  Status compressMore();
+  size_t sizeOfChunkOffsets() const {
+    return chunkOffsets.length() * sizeof(chunkOffsets[0]);
+  }
+
+  // Returns the number of bytes needed to store the data currently written +
+  // the chunk offsets.
+  size_t totalBytesNeeded() const;
+
+  // Append the chunk offsets to |dest|.
+  void finish(char* dest, size_t destBytes);
+
+  static void rangeToChunkAndOffset(size_t uncompressedStart,
+                                    size_t uncompressedLimit,
+                                    size_t* firstChunk,
+                                    size_t* firstChunkOffset,
+                                    size_t* firstChunkSize, size_t* lastChunk,
+                                    size_t* lastChunkSize) {
+    *firstChunk = uncompressedStart / CHUNK_SIZE;
+    *firstChunkOffset = uncompressedStart % CHUNK_SIZE;
+    *firstChunkSize = CHUNK_SIZE - *firstChunkOffset;
+
+    MOZ_ASSERT(uncompressedStart < uncompressedLimit,
+               "subtraction below requires a non-empty range");
+
+    *lastChunk = (uncompressedLimit - 1) / CHUNK_SIZE;
+    *lastChunkSize = ((uncompressedLimit - 1) % CHUNK_SIZE) + 1;
+  }
+
+  static size_t chunkSize(size_t uncompressedBytes, size_t chunk) {
+    MOZ_ASSERT(uncompressedBytes > 0, "must have uncompressed data to chunk");
+
+    size_t startOfChunkBytes = chunk * CHUNK_SIZE;
+    MOZ_ASSERT(startOfChunkBytes < uncompressedBytes,
+               "chunk must refer to bytes not exceeding "
+               "|uncompressedBytes|");
+
+    size_t remaining = uncompressedBytes - startOfChunkBytes;
+    return remaining < CHUNK_SIZE ? remaining : CHUNK_SIZE;
+  }
+};
+
+/*
+ * Decompress a string. The caller must know the length of the output and
+ * allocate |out| to a string of that length.
+ */
+bool DecompressString(const unsigned char* inp, size_t inplen,
+                      unsigned char* out, size_t outlen);
+
+/*
+ * Decompress a single chunk of at most Compressor::CHUNK_SIZE bytes.
+ * |chunk| is the chunk index. The caller must know the length of the output
+ * (the uncompressed chunk) and allocate |out| to a string of that length.
+ */
+bool DecompressStringChunk(const unsigned char* inp, size_t chunk,
+                           unsigned char* out, size_t outlen);
+
+} /* namespace js */
+
+#endif /* vm_Compression_h */