From afe7cf78d51b819dcdc5b0f4cb85a25a52a9fcd0 Mon Sep 17 00:00:00 2001 From: Mark Adler Date: Wed, 7 Dec 2011 23:57:37 -0800 Subject: Enable dictionary setting in middle of stream, and keeping the dictionary. This patch adds the deflateResetKeep() function to retain the sliding window for the next deflate operation, and fixes an inflateResetKeep() problem that came from inflate() not updating the window when the stream completed. This enables constructing and decompressing a series of concatenated deflate streams where each can depend on the history of uncompressed data that precedes it. This generalizes deflateSetDictionary() and inflateSetDictionary() to permit setting the dictionary in the middle of a stream for raw deflate and inflate. This in combination with the Keep functions enables a scheme for updating files block by block with the transmission of compressed data, where blocks are sent with deflateResetKeep() to retain history for better compression, and deflateSetDictionary() is used for blocks already present at the receiver to skip compression but insert that data in the history, again for better compression. The corresponding inflate calls are done on the receiver side. --- zlib.h | 27 +++++++++++++++++---------- 1 file changed, 17 insertions(+), 10 deletions(-) (limited to 'zlib.h') diff --git a/zlib.h b/zlib.h index 3121b0a..3669f2e 100644 --- a/zlib.h +++ b/zlib.h @@ -581,10 +581,15 @@ ZEXTERN int ZEXPORT deflateSetDictionary OF((z_streamp strm, uInt dictLength)); /* Initializes the compression dictionary from the given byte sequence - without producing any compressed output. This function must be called - immediately after deflateInit, deflateInit2 or deflateReset, before any call - of deflate. The compressor and decompressor must use exactly the same - dictionary (see inflateSetDictionary). + without producing any compressed output. When using the zlib format, this + function must be called immediately after deflateInit, deflateInit2 or + deflateReset, and before any call of deflate. When doing raw deflate, this + function must be called either before any call of deflate, or immediately + after the completion of a deflate block, i.e. after all input has been + consumed and all output has been delivered when using any of the flush + options Z_BLOCK, Z_PARTIAL_FLUSH, Z_SYNC_FLUSH, or Z_FULL_FLUSH. The + compressor and decompressor must use exactly the same dictionary (see + inflateSetDictionary). The dictionary should consist of strings (byte sequences) that are likely to be encountered later in the data to be compressed, with the most commonly @@ -611,8 +616,8 @@ ZEXTERN int ZEXPORT deflateSetDictionary OF((z_streamp strm, deflateSetDictionary returns Z_OK if success, or Z_STREAM_ERROR if a parameter is invalid (e.g. dictionary being Z_NULL) or the stream state is inconsistent (for example if deflate has already been called for this stream - or if the compression method is bsort). deflateSetDictionary does not - perform any compression: this will be done by deflate(). + or if not at a block boundary for raw deflate). deflateSetDictionary does + not perform any compression: this will be done by deflate(). */ ZEXTERN int ZEXPORT deflateCopy OF((z_streamp dest, @@ -810,10 +815,11 @@ ZEXTERN int ZEXPORT inflateSetDictionary OF((z_streamp strm, if that call returned Z_NEED_DICT. The dictionary chosen by the compressor can be determined from the adler32 value returned by that call of inflate. The compressor and decompressor must use exactly the same dictionary (see - deflateSetDictionary). For raw inflate, this function can be called - immediately after inflateInit2() or inflateReset() and before any call of - inflate() to set the dictionary. The application must insure that the - dictionary that was used for compression is provided. + deflateSetDictionary). For raw inflate, this function can be called at any + time to set the dictionary. If the provided dictionary is smaller than the + window and there is already data in the window, then the provided dictionary + will amend what's there. The application must insure that the dictionary + that was used for compression is provided. inflateSetDictionary returns Z_OK if success, Z_STREAM_ERROR if a parameter is invalid (e.g. dictionary being Z_NULL) or the stream state is @@ -1694,6 +1700,7 @@ ZEXTERN int ZEXPORT inflateSyncPoint OF((z_streamp)); ZEXTERN const uLongf * ZEXPORT get_crc_table OF((void)); ZEXTERN int ZEXPORT inflateUndermine OF((z_streamp, int)); ZEXTERN int ZEXPORT inflateResetKeep OF((z_streamp)); +ZEXTERN int ZEXPORT deflateResetKeep OF((z_streamp)); #ifndef Z_SOLO ZEXTERN unsigned long ZEXPORT gzflags OF((void)); #endif -- cgit v1.2.3-55-g6feb