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* Copyright (c) 1999-2009, PostgreSQL Global Development Group
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* $PostgreSQL: pgsql/src/backend/utils/adt/pg_lzcompress.c,v 1.33 2009/01/06 15:51:38 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/utils/adt/pg_lzcompress.c,v 1.34 2009/06/11 14:49:03 momjian Exp $
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#include "postgres.h"
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static const PGLZ_Strategy strategy_default_data = {
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32, /* Data chunks less than 32 bytes are not compressed */
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INT_MAX, /* No upper limit on what we'll try to compress */
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25, /* Require 25% compression rate, or not worth it */
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1024, /* Give up if no compression in the first 1KB */
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128, /* Stop history lookup if a match of 128 bytes is found */
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10 /* Lower good match size by 10% at every loop iteration */
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32, /* Data chunks less than 32 bytes are not
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INT_MAX, /* No upper limit on what we'll try to
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25, /* Require 25% compression rate, or not worth
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1024, /* Give up if no compression in the first 1KB */
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128, /* Stop history lookup if a match of 128 bytes
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10 /* Lower good match size by 10% at every loop
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const PGLZ_Strategy *const PGLZ_strategy_default = &strategy_default_data;
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static const PGLZ_Strategy strategy_always_data = {
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0, /* Chunks of any size are compressed */
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0, /* Chunks of any size are compressed */
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0, /* It's enough to save one single byte */
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INT_MAX, /* Never give up early */
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128, /* Stop history lookup if a match of 128 bytes is found */
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6 /* Look harder for a good match */
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0, /* It's enough to save one single byte */
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INT_MAX, /* Never give up early */
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128, /* Stop history lookup if a match of 128 bytes
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6 /* Look harder for a good match */
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const PGLZ_Strategy *const PGLZ_strategy_always = &strategy_always_data;
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strategy = PGLZ_strategy_default;
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* If the strategy forbids compression (at all or if source chunk size
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* out of range), fail.
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* If the strategy forbids compression (at all or if source chunk size out
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if (strategy->match_size_good <= 0 ||
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slen < strategy->min_input_size ||
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* Compute the maximum result size allowed by the strategy, namely
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* the input size minus the minimum wanted compression rate. This had
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* better be <= slen, else we might overrun the provided output buffer.
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* Compute the maximum result size allowed by the strategy, namely the
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* input size minus the minimum wanted compression rate. This had better
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* be <= slen, else we might overrun the provided output buffer.
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if (slen > (INT_MAX/100))
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if (slen > (INT_MAX / 100))
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/* Approximate to avoid overflow */
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result_max = (slen / 100) * (100 - need_rate);
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* If we've emitted more than first_success_by bytes without finding
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* anything compressible at all, fail. This lets us fall out
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* anything compressible at all, fail. This lets us fall out
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* reasonably quickly when looking at incompressible input (such as
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* pre-compressed data).
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while (sp < srcend && dp < destend)
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* Read one control byte and process the next 8 items (or as many
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* as remain in the compressed input).
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* Read one control byte and process the next 8 items (or as many as
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* remain in the compressed input).
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unsigned char ctrl = *sp++;
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for (ctrlc = 0; ctrlc < 8 && sp < srcend; ctrlc++)
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* Check for output buffer overrun, to ensure we don't
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* clobber memory in case of corrupt input. Note: we must
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* advance dp here to ensure the error is detected below
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* the loop. We don't simply put the elog inside the loop
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* since that will probably interfere with optimization.
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* Check for output buffer overrun, to ensure we don't clobber
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* memory in case of corrupt input. Note: we must advance dp
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* here to ensure the error is detected below the loop. We
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* don't simply put the elog inside the loop since that will
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* probably interfere with optimization.
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if (dp + len > destend)
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* An unset control bit means LITERAL BYTE. So we just copy
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* one from INPUT to OUTPUT.
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if (dp >= destend) /* check for buffer overrun */
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break; /* do not clobber memory */
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if (dp >= destend) /* check for buffer overrun */
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break; /* do not clobber memory */
added
removed
src/backend/utils/adt/pg_lzcompress.c
