LZW encoder by Bartlomiej Wolowiec b.wolowiec students mimuw edu pl

Originally committed as revision 8644 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/lzw.h

@@ -30,6 +30,8 @@
 #ifndef LZW_H
 #define LZW_H
 
+#include "bitstream.h"
+
 enum FF_LZW_MODES{
     FF_LZW_GIF,
     FF_LZW_TIFF
@@ -46,4 +48,12 @@ int ff_lzw_decode(LZWState *s, uint8_t *buf, int len);
 uint8_t* ff_lzw_cur_ptr(LZWState *lzw);
 void ff_lzw_decode_tail(LZWState *lzw);
 
+/** LZW encode state */
+struct LZWEncodeState;
+extern const int ff_lzw_encode_state_size;
+
+void ff_lzw_encode_init(struct LZWEncodeState * s, uint8_t * outbuf, int outsize, int maxbits);
+int ff_lzw_encode(struct LZWEncodeState * s, const uint8_t * inbuf, int insize);
+int ff_lzw_encode_flush(struct LZWEncodeState * s);
+
 #endif

libavcodec/lzwenc.c

+/*
+ * LZW encoder
+ * Copyright (c) 2007 Bartlomiej Wolowiec
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * LZW encoder
+ * @file lzwenc.c
+ * @author Bartlomiej Wolowiec
+ */
+
+#include "avcodec.h"
+#include "bitstream.h"
+#include "lzw.h"
+
+#define LZW_MAXBITS 12
+#define LZW_SIZTABLE (1<<LZW_MAXBITS)
+#define LZW_HASH_SIZE 16411
+#define LZW_HASH_SHIFT 6
+
+#define LZW_PREFIX_EMPTY -1
+#define LZW_PREFIX_FREE -2
+
+/** One code in hash table */
+typedef struct Code{
+    /// Hash code of prefix, LZW_PREFIX_EMPTY if empty prefix, or LZW_PREFIX_FREE if no code
+    int hash_prefix;
+    int code;               ///< LZW code
+    uint8_t suffix;         ///< Last character in code block
+}Code;
+
+/** LZW encode state */
+typedef struct LZWEncodeState {
+    int clear_code;          ///< Value of clear code
+    int end_code;            ///< Value of end code
+    Code tab[LZW_HASH_SIZE]; ///< Hash table
+    int tabsize;             ///< Number of values in hash table
+    int bits;                ///< Actual bits code
+    int bufsize;             ///< Size of output buffer
+    PutBitContext pb;        ///< Put bit context for output
+    int maxbits;             ///< Max bits code
+    int maxcode;             ///< Max value of code
+    int output_bytes;        ///< Number of written bytes
+    int last_code;           ///< Value of last output code or LZW_PREFIX_EMPTY
+}LZWEncodeState;
+
+
+const int ff_lzw_encode_state_size = sizeof(LZWEncodeState);
+
+/**
+ * Hash function adding character
+ * @param head LZW code for prefix
+ * @param add Character to add
+ * @return New hash value
+ */
+static inline int hash(int head, const int add)
+{
+    head ^= (add << LZW_HASH_SHIFT);
+    if (head >= LZW_HASH_SIZE)
+        head -= LZW_HASH_SIZE;
+    assert(head >= 0 && head < LZW_HASH_SIZE);
+    return head;
+}
+
+/**
+ * Hash function calculates next hash value
+ * @param head Actual hash code
+ * @param offset Offset calculated by hashOffset
+ * @return New hash value
+ */
+static inline int hashNext(int head, const int offset)
+{
+    head -= offset;
+    if(head < 0)
+        head += LZW_HASH_SIZE;
+    return head;
+}
+
+/**
+ * Hash function calculates hash offset
+ * @param head Actual hash code
+ * @return Hash offset
+ */
+static inline int hashOffset(const int head)
+{
+    return head ? LZW_HASH_SIZE - head : 1;
+}
+
+/**
+ * Write one code to stream
+ * @param s LZW state
+ * @param c code to write
+ */
+static inline void writeCode(LZWEncodeState * s, int c)
+{
+    assert(0 <= c && c < 1 << s->bits);
+    put_bits(&s->pb, s->bits, c);
+}
+
+
+/**
+ * Find LZW code for block
+ * @param s LZW state
+ * @param c Last character in block
+ * @param hash_prefix LZW code for prefix
+ * @return LZW code for block or -1 if not found in table
+ */
+static inline int findCode(LZWEncodeState * s, uint8_t c, int hash_prefix)
+{
+    int h = hash(FFMAX(hash_prefix, 0), c);
+    int hash_offset = hashOffset(h);
+
+    while (s->tab[h].hash_prefix != LZW_PREFIX_FREE) {
+        if ((s->tab[h].suffix == c)
+            && (s->tab[h].hash_prefix == hash_prefix))
+            return h;
+        h = hashNext(h, hash_offset);
+    }
+
+    return h;
+}
+
+/**
+ * Add block to LZW code table
+ * @param s LZW state
+ * @param c Last character in block
+ * @param hash_prefix LZW code for prefix
+ * @param hash_code LZW code for bytes block
+ */
+static inline void addCode(LZWEncodeState * s, uint8_t c, int hash_prefix, int hash_code)
+{
+    s->tab[hash_code].code = s->tabsize;
+    s->tab[hash_code].suffix = c;
+    s->tab[hash_code].hash_prefix = hash_prefix;
+
+    s->tabsize++;
+
+    if (s->tabsize >= 1 << s->bits)
+        s->bits++;
+}
+
+/**
+ * Clear LZW code table
+ * @param s LZW state
+ */
+static void clearTable(LZWEncodeState * s)
+{
+    int i, h;
+
+    writeCode(s, s->clear_code);
+    s->bits = 9;
+    for (i = 0; i < LZW_HASH_SIZE; i++) {
+        s->tab[i].hash_prefix = LZW_PREFIX_FREE;
+    }
+    for (i = 0; i < 256; i++) {
+        h = hash(0, i);
+        s->tab[h].code = i;
+        s->tab[h].suffix = i;
+        s->tab[h].hash_prefix = LZW_PREFIX_EMPTY;
+    }
+    s->tabsize = 258;
+}
+
+/**
+ * Calculate number of bytes written
+ * @param s LZW encode state
+ * @return Number of bytes written
+ */
+static int writtenBytes(LZWEncodeState *s){
+    int ret = (put_bits_count(&s->pb)) >> 3;
+    ret -= s->output_bytes;
+    s->output_bytes += ret;
+    return ret;
+}
+
+/**
+ * Initialize LZW encoder. Please set s->clear_code, s->end_code and s->maxbits before run.
+ * @param s LZW state
+ * @param outbuf Output buffer
+ * @param outsize Size of output buffer
+ * @param maxbits Maximum length of code
+ */
+void ff_lzw_encode_init(LZWEncodeState * s, uint8_t * outbuf, int outsize, int maxbits)
+{
+    s->clear_code = 256;
+    s->end_code = 257;
+    s->maxbits = maxbits;
+    init_put_bits(&s->pb, outbuf, outsize);
+    s->bufsize = outsize;
+    assert(9 <= s->maxbits && s->maxbits <= s->maxbits);
+    s->maxcode = 1 << s->maxbits;
+    s->output_bytes = 0;
+    s->last_code = LZW_PREFIX_EMPTY;
+    s->bits = 9;
+}
+
+/**
+ * LZW main compress function
+ * @param s LZW state
+ * @param inbuf Input buffer
+ * @param insize Size of input buffer
+ * @return Number of bytes written or -1 on error
+ */
+int ff_lzw_encode(LZWEncodeState * s, const uint8_t * inbuf, int insize)
+{
+    int i;
+    int code_prefix = s->last_code;
+
+    if(insize * 3 > (s->bufsize - s->output_bytes) * 2){
+        return -1;
+    }
+
+    if (code_prefix == LZW_PREFIX_EMPTY)
+        clearTable(s);
+
+    for (i = 0; i < insize; i++) {
+        uint8_t c = *inbuf++;
+        int code = findCode(s, c, code_prefix);
+        if (s->tab[code].hash_prefix != LZW_PREFIX_FREE) {
+            code_prefix = s->tab[code].code;
+        } else {
+            writeCode(s, code_prefix);
+            addCode(s, c, code_prefix, code);
+            code_prefix = s->tab[hash(0, c)].code;
+        }
+        if (s->tabsize >= s->maxcode - 1) {
+            clearTable(s);
+        }
+    }
+    s->last_code = code_prefix;
+
+    return writtenBytes(s);
+}
+
+/**
+ * Write end code and flush bitstream
+ * @param s LZW state
+ * @return Number of bytes written or -1 on error
+ */
+int ff_lzw_encode_flush(LZWEncodeState * s)
+{
+    if (s->last_code != -1)
+        writeCode(s, s->last_code);
+    writeCode(s, s->end_code);
+    flush_put_bits(&s->pb);
+    s->last_code = -1;
+
+    return writtenBytes(s);
+}