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[/] [or1k/] [trunk/] [ecos-2.0/] [packages/] [fs/] [jffs2/] [v2_0/] [src/] [compr_rtime.c] - Rev 1765
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/* * JFFS2 -- Journalling Flash File System, Version 2. * * Copyright (C) 2001, 2002 Red Hat, Inc. * * Created by Arjan van de Ven <arjanv@redhat.com> * * For licensing information, see the file 'LICENCE' in this directory. * * $Id: compr_rtime.c,v 1.1.1.1 2004-02-14 13:29:19 phoenix Exp $ * * * Very simple lz77-ish encoder. * * Theory of operation: Both encoder and decoder have a list of "last * occurances" for every possible source-value; after sending the * first source-byte, the second byte indicated the "run" length of * matches * * The algorithm is intended to only send "whole bytes", no bit-messing. * */ #include <linux/kernel.h> #include <linux/types.h> #include <linux/errno.h> #include <linux/string.h> /* _compress returns the compressed size, -1 if bigger */ int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out, uint32_t *sourcelen, uint32_t *dstlen) { int positions[256]; int outpos = 0; int pos=0; memset(positions,0,sizeof(positions)); while (pos < (*sourcelen) && outpos <= (*dstlen)-2) { int backpos, runlen=0; unsigned char value; value = data_in[pos]; cpage_out[outpos++] = data_in[pos++]; backpos = positions[value]; positions[value]=pos; while ((backpos < pos) && (pos < (*sourcelen)) && (data_in[pos]==data_in[backpos++]) && (runlen<255)) { pos++; runlen++; } cpage_out[outpos++] = runlen; } if (outpos >= pos) { /* We failed */ return -1; } /* Tell the caller how much we managed to compress, and how much space it took */ *sourcelen = pos; *dstlen = outpos; return 0; } void jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out, uint32_t srclen, uint32_t destlen) { int positions[256]; int outpos = 0; int pos=0; memset(positions,0,sizeof(positions)); while (outpos<destlen) { unsigned char value; int backoffs; int repeat; value = data_in[pos++]; cpage_out[outpos++] = value; /* first the verbatim copied byte */ repeat = data_in[pos++]; backoffs = positions[value]; positions[value]=outpos; if (repeat) { if (backoffs + repeat >= outpos) { while(repeat) { cpage_out[outpos++] = cpage_out[backoffs++]; repeat--; } } else { memcpy(&cpage_out[outpos],&cpage_out[backoffs],repeat); outpos+=repeat; } } } }