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46 lines
3 KiB
C
46 lines
3 KiB
C
/* -*- mode: C; c-basic-offset: 4 -*- */
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#ifndef TOKU_COMPRESS_H
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#define TOKU_COMPRESS_H
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#ident "$Id$"
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#include <zlib.h>
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#include <db.h>
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// The following provides an abstraction of quicklz and zlib.
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// We offer three compression methods: ZLIB, QUICKLZ, and LZMA, as well as a "no compression" option. These options are declared in make_tdb.c.
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// The resulting byte string includes enough information for us to decompress it. That is, we can tell whether it's z-compressed or qz-compressed or xz-compressed.
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size_t toku_compress_bound (enum toku_compression_method a, size_t size);
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// Effect: Return the number of bytes needed to compress a buffer of size SIZE using compression method A.
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// Typically, the result is a little bit larger than SIZE, since some data cannot be compressed.
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// Usage note: It may help to know roughly how much space is involved.
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// zlib's bound is something like (size + (size>>12) + (size>>14) + (size>>25) + 13.
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// quicklz's bound is something like size+400.
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void toku_compress (enum toku_compression_method a,
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// the following types and naming conventions come from zlib.h
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Bytef *dest, uLongf *destLen,
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const Bytef *source, uLong sourceLen);
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// Effect: Using compression method A, compress SOURCE into DEST. The number of bytes to compress is passed in SOURCELEN.
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// On input: *destLen is the size of the buffer.
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// On output: *destLen is the size of the actual compressed data.
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// Usage note: sourceLen may be be zero (unlike for quicklz, which requires sourceLen>0).
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// Requires: The buffer must be big enough to hold the compressed data. (That is *destLen >= compressBound(a, sourceLen))
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// Requires: sourceLen < 2^32.
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// Usage note: Although we *try* to assert if the DESTLEN isn't big enough, it's possible that it's too late by then (in the case of quicklz which offers
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// no way to avoid a buffer overrun.) So we require that that DESTLEN is big enough.
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// Rationale: zlib's argument order is DEST then SOURCE with the size of the buffer passed in *destLen, and the size of the result returned in *destLen.
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// quicklz's argument order is SOURCE then DEST with the size returned (and it has no way to verify that an overright didn't happen).
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// We use zlib's calling conventions partly because it is safer, and partly because it is more established.
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// We also use zlib's ugly camel case convention for destLen and sourceLen.
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// Unlike zlib, we return no error codes. Instead, we require that the data be OK and the size of the buffers is OK, and assert if there's a problem.
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void toku_decompress (Bytef *dest, uLongf destLen,
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const Bytef *source, uLongf sourceLen);
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// Effect: Decompress source (length sourceLen) into dest (length destLen)
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// This function can decompress data compressed with either zlib or quicklz compression methods (calling toku_compress(), which puts an appropriate header on so we know which it is.)
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// Requires: destLen is equal to the actual decompressed size of the data.
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// Requires: The source must have been properly compressed.
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#endif
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