js/src/vm/Compression.h
author Eugen Sawin <esawin@mozilla.com>
Mon, 18 Sep 2017 22:09:37 +0200
changeset 383197 505c1e22424aa59809ccf33cec9bf1d20d784c2a
parent 316155 a92b2f6ab6ad5279682451506da866f926d27be9
child 405100 0ceb91c42b0ff876a61ed23f5e587ba3a2083bcf
permissions -rw-r--r--
Bug 1401002 - [1.1] Don't override chrome window type with default argument value. r=tromey

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * 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 "jsalloc.h"
#include "jstypes.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 const size_t CHUNK_SIZE = 64 * 1024;

  private:
    // Number of bytes we should hand to zlib each compressMore() call.
    static const 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 toChunkOffset(size_t uncompressedOffset, size_t* chunk, size_t* chunkOffset) {
        *chunk = uncompressedOffset / CHUNK_SIZE;
        *chunkOffset = uncompressedOffset % CHUNK_SIZE;
    }
    static size_t chunkSize(size_t uncompressedBytes, size_t chunk) {
        MOZ_ASSERT(uncompressedBytes > 0);
        size_t lastChunk = (uncompressedBytes - 1) / CHUNK_SIZE;
        MOZ_ASSERT(chunk <= lastChunk);
        if (chunk < lastChunk || uncompressedBytes % CHUNK_SIZE == 0)
            return CHUNK_SIZE;
        return uncompressedBytes % 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 */