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/* -*- 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 */
#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 {
// 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;
// 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;
Compressor(const unsigned char* inp, size_t inplen);
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 "
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 */