ZLib

This SWI is similar to SWI Squash_Compress, providing a drop in replacement for the Squash module but using ZLib compression. There are two variants of this SWI - with bit 3 set, and with bit 3 clear. Normally, this call will be made first with bit 3 set to read the workspace size, and then with bit 3 clear to perform the decompression.

This SWI is used to read the size of the buffers to use for ZLib compression via the Squash-like interface.

This SWI is used to compress data to a buffer.

This SWI is similar to SWI Squash_Compress, providing a drop in replacement for the Squash module but using ZLib decompression. There are two variants of this SWI - with bit 3 set, and with bit 3 clear. Normally, this call will be made first with bit 3 set to read the workspace size, and then with bit 3 clear to perform the decompression.

This SWI is used to read the size of the buffers to use for ZLib decompression via the Squash-like interface.

This SWI is used to decompress data from a buffer.

This SWI is used to update a running CRC-32 checksum with data from a buffer. The returned CRC-32 value should be passed back to the this SWI if the checksum needs updating further. ZLib_CRC32 is a slower call than OS_CRC, but more reliable.

This SWI is used to update a running Adler-32 checksum with data from a buffer. The returned Adler-32 value should be passed back to the this SWI if the checksum needs updating further. Adler-32 is a faster checksum to calculate than CRC-32.

This SWI is used to read the version number of the ZLib library in use.

This SWI is used to compress a block of data in a single call. The output buffer must be at least 0.1% larger than the input, plus 12 bytes.

This SWI is equivilent to ZLib_Compress, but allows the compression level to be specified.

This SWI decompresses a buffer of data in a single call. The destination buffer must be large enough for the decompressed data.

This SWI is used to initialise the ZLib compression algorithm. You should clear the workspace block to zeros. zalloc and zfree may point to routines to allocate and free memory. If these are not set then memory is allocated on a per application basis in the global dynamic area. zalloc and zfree will be entered within a C environment (ie APCS applies) with a small stack, in SVC mode. Because of this, you cannot use longjmp, use functions that require large amounts of stack space, or perform any non-SVC mode operation. Contact RISCOS Ltd if you wish to use this feature but are unsure how it will affect your code.

This SWI is used to initialise the ZLib stream decompression algorithm. You should clear the workspace block to zeros. zalloc and zfree may point to routines to allocate and free memory. If these are not set then memory is allocated on a per application basis in the global dynamic area. zalloc and zfree will be entered within a C environment (ie APCS applies) with a small stack, in SVC mode. Because of this, you cannot use longjmp, use functions that require large amounts of stack space, or perform any non-SVC mode operation. Contact RISCOS Ltd if you wish to use this feature but are unsure how it will affect your code.

This SWI is similar to ZLib_DeflateInit, but provides much greater control than that SWI.

This SWI is similar to ZLib_InflateInit, but provides much greater control than that SWI.

This SWI compresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full. next_in and avail_in are read and updated after data has been processed. You should empty the output buffer when data appears there (next_out and avail_out will have been updated).

ZLib_Deflate performs one or both of the following actions:

• Compress more input starting at next_in and update next_in and avail_in accordingly. If not all input can be processed (because there is not enough room in the output buffer), next_in and avail_in are updated and processing will resume at this point for the next call of ZLib_Deflate.
• Provide more output starting at next_out and update next_out and avail_out accordingly. This action is forced if the parameter flush is non zero. Forcing flush frequently degrades the compression ratio, so this parameter should be set only when necessary (in interactive applications). Some output may be provided even if flush is not set.

Before calling ZLib_Deflate, the client should ensure that at least one of the actions is possible, by providing more input and/or consuming more output, and updating avail_in or avail_out accordingly; avail_out should never be zero before the call. The client may consume the compressed output when it wants, for example when the output buffer is full (avail_out == 0), or after each call of ZLib_Deflate. If deflate returns Z_OK and with zero avail_out, it must be called again after making room in the output buffer because there might be more output pending.

If the flush type is set to Z_SYNC_FLUSH, all pending output is flushed to the output buffer and the output is aligned on a byte boundary, so that the decompressor can get all input data available so far. In particular avail_in is zero after the call if enough output space has been provided before the call. Flushing may degrade compression for some compression algorithms and so it should be used only when necessary.

If the flush type is set to Z_FULL_FLUSH, all output is flushed as with Z_SYNC_FLUSH, and the compression state is reset so that decompression can restart from this point if previous compressed data has been damaged or if random access is desired. Using Z_FULL_FLUSH too often can seriously degrade the compression.

If deflate returns with avail_out == 0, this function must be called again with the same value of the flush parameter and more output space (updated avail_out), until the flush is complete (ZLib_Deflate returns with non-zero avail_out).

If the flush type is set to Z_FINISH, pending input is processed, pending output is flushed and ZLib_Deflate returns with Z_STREAM_END if there was enough output space; if ZLib_Deflate returns with Z_OK, this function must be called again with Z_FINISH and more output space (updated avail_out) but no more input data, until it returns with Z_STREAM_END or an error. After ZLib_Deflate has returned Z_STREAM_END, the only possible operations on the stream are SWI ZLib_DeflateReset or SWI ZLib_DeflateEnd.

Z_FINISH can be used immediately after SWI ZLib_DeflateInit if all the compression is to be done in a single step. In this case, avail_out must be at least 0.1% larger than avail_in plus 12 bytes. If ZLib_Deflate does not return Z_STREAM_END, then it must be called again as described above.

ZLib_Deflate sets adler to the adler32 checksum of all input read so far (that is, total_in bytes).

ZLib_Deflate may update data_type if it can make a good guess about the input data type (Z_ASCII or Z_BINARY). In doubt, the data is considered binary. This field is only for information purposes and does not affect the compression algorithm in any manner.

ZLib_Deflate returns Z_OK if some progress has been made (more input processed or more output produced), Z_STREAM_END if all input has been consumed and all output has been produced (only when the flush type is set to Z_FINISH), Z_STREAM_ERROR if the stream state was inconsistent (for example if next_in or next_out was NULL), Z_BUF_ERROR if no progress is possible (for example avail_in or avail_out was zero).

This SWI frees all the memory used by the compression algorithm, discarding any unprocessed input or output.

This SWI decompresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full. next_in and avail_in are read and updated after data has been processed. You should empty the output buffer when data appears there (next_out and avail_out will have been updated).

ZLib_Inflate performs one or both of the following actions:

• Decompress more input starting at next_in and update next_in and avail_in accordingly. If not all input can be processed (because there is not enough room in the output buffer), next_in is updated and processing will resume at this point for the next call of ZLib_Inflate.
• Provide more output starting at next_out and update next_out and avail_out accordingly. ZLib_Inflate provides as much output as possible, until there is no more input data or no more space in the output buffer (see below about the flush parameter).

Before the call of ZLib_Inflate, the application should ensure that at least one of the actions is possible, by providing more input and/or consuming more output, and updating the next_in/next_out and avail_in/avail_out values accordingly. The application can consume the uncompressed output when it wants, for example when the output buffer is full (avail_out == 0), or after each call of ZLib_Inflate. If this SWI returns Z_OK and with zero avail_out, it must be called again after making room in the output buffer because there might be more output pending.

If R1 is set to Z_SYNC_FLUSH, ZLib_Inflate flushes as much output as possible to the output buffer. The flushing behavior of inflate is not specified for values of the flush parameter other than Z_SYNC_FLUSH and Z_FINISH, but the current implementation actually flushes as much output as possible anyway.

ZLib_Inflate should normally be called until it returns Z_STREAM_END or an error. However if all decompression is to be performed in a single step (a single call of ZLib_Inflate), the parameter flush should be set to Z_FINISH. In this case all pending input is processed and all pending output is flushed ; avail_out must be large enough to hold all the uncompressed data. (The size of the uncompressed data may have been saved by the compressor for this purpose.) The next operation on this stream must be inflateEnd to deallocate the decompression state. The use of Z_FINISH is never required, but can be used to inform inflate that a faster routine may be used for the single ZLib_Inflate call.

If a preset dictionary is needed at this point (see #swi_zlib_inflatesetdictionary below), ZLib_Inflate sets adler to the Adler-32 checksum of the dictionary chosen by the compressor and returns Z_NEED_DICT ; otherwise it sets adler to the Adler-32 checksum of all output produced so far (that is, total_out bytes) and returns Z_OK, Z_STREAM_END or an error code as described below. At the end of the stream, ZLib_Inflate checks that its computed Adler-32 checksum is equal to that saved by the compressor and returns Z_STREAM_END only if the checksum is correct.

ZLib_Inflate returns Z_OK if some progress has been made (more input processed or more output produced), Z_STREAM_END if the end of the compressed data has been reached and all uncompressed output has been produced, Z_NEED_DICT if a preset dictionary is needed at this point, Z_DATA_ERROR if the input data was corrupted (input stream not conforming to the ZLib format or incorrect Adler-32 checksum), Z_STREAM_ERROR if the stream structure was inconsistent (for example if next_in or next_out was NULL), Z_MEM_ERROR if there was not enough memory, Z_BUF_ERROR if no progress is possible or if there was not enough room in the output buffer when Z_FINISH is used. In the Z_DATA_ERROR case, the application may then call SWI ZLib_InflateSync to look for a good compression block.

This SWI frees all the memory used by the decompression algorithm, discarding any unprocessed input or output.

This SWI is used to initialise a compression dictionary. The dictionary consists of strings (byte sequences) that are likely to be encountered later in the data to be compressed, with the most commonly used strings preferably put towards the end of the dictionary.

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 used strings preferably put towards the end of the dictionary. Using a dictionary is most useful when the data to be compressed is short and can be predicted with good accuracy ; the data can then be compressed better than with the default empty dictionary.

Depending on the size of the compression data structures selected by ZLib_DeflateInit or ZLib_DeflateInit2, a part of the dictionary may in effect be discarded, for example if the dictionary is larger than the window size in ZLib_Deflate or ZLib_Deflate2. Thus the strings most likely to be useful should be put at the end of the dictionary, not at the front.

Upon return of this function, adler is set to the Adler-32 value of the dictionary; the decompressor may later use this value to determine which dictionary has been used by the compressor. (The Adler32 value applies to the whole dictionary even if only a subset of the dictionary is actually used by the compressor.)

ZLib_DeflateSetDictionary returns Z_OK if success, or Z_STREAM_ERROR if a parameter is invalid (such as NULL dictionary) or the stream state is inconsistent (for example if ZLib_Deflate has already been called for this stream). ZLib_DeflateSetDictionary does not perform any compression: this will be done by ZLib_Deflate.

This SWI is used to take a copy of the current compression state. This might be useful if you are attempting to filter the data in one of a number of ways.

This SWI is equivilent to ZLib_DeflateEnd followed by ZLib_DeflateInit.

This SWI is updates the compression level and strategy. You may do this part way through compression.

This SWI is used to initialise a decompression dictionary. The dictionary must be the same as that used to compress the data (ZLib_DeflateSetDictionary).

This SWI will skip invalid data until a full flush point is found. This may be useful if you have data which is likely to be corrupted, is periodically synchronised and the data 'lost' is unimportant. An example might be a stream of graphical or audio data.

This SWI is equivilent to ZLib_InflateEnd followed by ZLib_InflateInit.

This SWI opens a file for accessing GZip compressed data. The 'R' extension is intended for compressing RISC OS files completely losslessly. Expanding such files on other systems will result in the loss of RISC OS type information only; the file data itself will be intact.

This SWI reads data from a previously opened GZip file.

This SWI writes data to a previously opened GZip file.

This SWI writes data to a previously opened GZip file.

This SWI closes a previously opened GZip file.

This SWI returns the last error message returned by a GZip operation.

This SWI changes the pointer within a GZip file. The position specified is located such that byte number R1 had just been read from the file. The operation cannot be performed on files being written.

This SWI returns the current position in the decompressed data in bytes as an offset from the start of the data.

This SWI checks whether the end of the file has been reached.

This SWI is used to associate a ZLib stream with a task. When associated, the tasks death will cause the memory allocated to the stream to be released automatically. If dissociated, the stream will never be freed unless the deflateEnd or inflateEnd calls are issued.

By default all streams are associated with the task with which they were created and destroyed automatically should that task terminate. You may wish to disable this operation using this SWI.