diff options
Diffstat (limited to 'compr_rtime.c')
-rw-r--r-- | compr_rtime.c | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/compr_rtime.c b/compr_rtime.c new file mode 100644 index 0000000..ab8cce3 --- /dev/null +++ b/compr_rtime.c @@ -0,0 +1,122 @@ +/* + * JFFS2 -- Journalling Flash File System, Version 2. + * + * Copyright (C) 2001-2003 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 1.4 2005/11/07 11:15:09 gleixner Exp $ + * + * + * Very simple lz77-ish encoder. + * + * Theory of operation: Both encoder and decoder have a list of "last + * occurrences" 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 <stdint.h> +#include <string.h> +#include "compr.h" + +/* _compress returns the compressed size, -1 if bigger */ +static int jffs2_rtime_compress(unsigned char *data_in, unsigned char *cpage_out, + uint32_t *sourcelen, uint32_t *dstlen, void *model) +{ + short 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; +} + + +static int jffs2_rtime_decompress(unsigned char *data_in, unsigned char *cpage_out, + uint32_t srclen, uint32_t destlen, void *model) +{ + short 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; + } + } + } + return 0; +} + + +static struct jffs2_compressor jffs2_rtime_comp = { + .priority = JFFS2_RTIME_PRIORITY, + .name = "rtime", + .disabled = 0, + .compr = JFFS2_COMPR_RTIME, + .compress = &jffs2_rtime_compress, + .decompress = &jffs2_rtime_decompress, +}; + +int jffs2_rtime_init(void) +{ + return jffs2_register_compressor(&jffs2_rtime_comp); +} + +void jffs2_rtime_exit(void) +{ + jffs2_unregister_compressor(&jffs2_rtime_comp); +} |