diff -r 000000000000 -r 6474c204b198 mfbt/Compression.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mfbt/Compression.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,116 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+/* Various simple compression/decompression functions. */
+
+#ifndef mozilla_Compression_h_
+#define mozilla_Compression_h_
+
+#include "mozilla/Types.h"
+#include "mozilla/Assertions.h"
+
+namespace mozilla {
+namespace Compression {
+
+/**
+ * LZ4 is a very fast byte-wise compression algorithm.
+ *
+ * Compared to Google's Snappy it is faster to compress and decompress and
+ * generally produces output of about the same size.
+ *
+ * Compared to zlib it compresses at about 10x the speed, decompresses at about
+ * 4x the speed and produces output of about 1.5x the size.
+ *
+ */
+
+class LZ4
+{
+
+public:
+
+  /**
+   * Compresses 'inputSize' bytes from 'source' into 'dest'.
+   * Destination buffer must be already allocated,
+   * and must be sized to handle worst cases situations (input data not compressible)
+   * Worst case size evaluation is provided by function maxCompressedSize()
+   *
+   * @param inputSize is the input size. Max supported value is ~1.9GB
+   * @param return the number of bytes written in buffer dest
+   */
+  static MFBT_API size_t compress(const char* source, size_t inputSize, char* dest);
+
+  /**
+   * Compress 'inputSize' bytes from 'source' into an output buffer
+   * 'dest' of maximum size 'maxOutputSize'.  If it cannot achieve it,
+   * compression will stop, and result of the function will be zero,
+   * 'dest' will still be written to, but since the number of input
+   * bytes consumed is not returned the result is not usable.
+   *
+   * This function never writes outside of provided output buffer.
+   *
+   * @param inputSize is the input size. Max supported value is ~1.9GB
+   * @param maxOutputSize is the size of the destination buffer (which must be already allocated)
+   * @return the number of bytes written in buffer 'dest'
+             or 0 if the compression fails
+  */
+  static MFBT_API size_t compressLimitedOutput(const char* source, size_t inputSize, char* dest,
+                                               size_t maxOutputSize);
+
+  /**
+   * If the source stream is malformed, the function will stop decoding
+   * and return a negative result, indicating the byte position of the
+   * faulty instruction
+   *
+   * This function never writes outside of provided buffers, and never
+   * modifies input buffer.
+   *
+   * note : destination buffer must be already allocated.
+   *        its size must be a minimum of 'outputSize' bytes.
+   * @param outputSize is the output size, therefore the original size
+   * @return the number of bytes read in the source buffer
+  */
+  static MFBT_API bool decompress(const char* source, char* dest, size_t outputSize);
+
+  /**
+   * If the source stream is malformed, the function will stop decoding
+   * and return false.
+   *
+   * This function never writes beyond dest + maxOutputSize, and is
+   * therefore protected against malicious data packets.
+   *
+   * note   : Destination buffer must be already allocated.
+   *          This version is slightly slower than the decompress
+   *          without the maxOutputSize
+   *
+   * @param inputSize is the length of the input compressed data
+   * @param maxOutputSize is the size of the destination buffer (which must be already allocated)
+   * @param outputSize the actual number of bytes decoded in the destination buffer (necessarily <= maxOutputSize)
+
+  */
+  static MFBT_API bool decompress(const char* source, size_t inputSize, char* dest,
+                                  size_t maxOutputSize, size_t *outputSize);
+
+  /*
+    Provides the maximum size that LZ4 may output in a "worst case"
+    scenario (input data not compressible) primarily useful for memory
+    allocation of output buffer.
+    note : this function is limited by "int" range (2^31-1)
+
+    @param inputSize is the input size. Max supported value is ~1.9GB
+    @return maximum output size in a "worst case" scenario
+  */
+  static inline size_t maxCompressedSize(size_t inputSize)
+  {
+      size_t max = ((inputSize) + ((inputSize)/255) + 16);
+      MOZ_ASSERT(max > inputSize);
+      return max;
+  }
+
+};
+
+} /* namespace Compression */
+} /* namespace mozilla */
+
+#endif /* mozilla_Compression_h_ */