avcodec: Implement masked lz decompression

Signed-off-by: Umair Khan <omerjerk@gmail.com>

libavcodec/mlz.c

+/*
+ * Copyright (c) 2016 Umair Khan <omerjerk@gmail.com>
+ *
+ * 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
+ */
+
+#include "mlz.h"
+
+av_cold void ff_mlz_init_dict(void* context, MLZ *mlz) {
+    mlz->dict = av_malloc_array(TABLE_SIZE, sizeof(*mlz->dict));
+
+    mlz->flush_code            = FLUSH_CODE;
+    mlz->current_dic_index_max = DIC_INDEX_INIT;
+    mlz->dic_code_bit          = CODE_BIT_INIT;
+    mlz->bump_code             = (DIC_INDEX_INIT - 1);
+    mlz->next_code             = FIRST_CODE;
+    mlz->freeze_flag           = 0;
+    mlz->context               = context;
+}
+
+av_cold void ff_mlz_flush_dict(MLZ *mlz) {
+    MLZDict *dict = mlz->dict;
+    int i;
+    for ( i = 0; i < TABLE_SIZE; i++ ) {
+        dict[i].string_code = CODE_UNSET;
+        dict[i].parent_code = CODE_UNSET;
+        dict[i].match_len = 0;
+    }
+    mlz->current_dic_index_max = DIC_INDEX_INIT;
+    mlz->dic_code_bit          = CODE_BIT_INIT;  // DicCodeBitInit;
+    mlz->bump_code             = mlz->current_dic_index_max - 1;
+    mlz->next_code             = FIRST_CODE;
+    mlz->freeze_flag           = 0;
+}
+
+static void set_new_entry_dict(MLZDict* dict, int string_code, int parent_code, int char_code) {
+    dict[string_code].parent_code = parent_code;
+    dict[string_code].string_code = string_code;
+    dict[string_code].char_code   = char_code;
+    if (parent_code < FIRST_CODE) {
+        dict[string_code].match_len = 2;
+    } else {
+        dict[string_code].match_len = (dict[parent_code].match_len) + 1;
+    }
+}
+
+static int decode_string(MLZ* mlz, unsigned char *buff, int string_code, int *first_char_code, unsigned long bufsize) {
+    MLZDict* dict = mlz->dict;
+    unsigned long count, offset;
+    int current_code, parent_code, tmp_code;
+
+    count            = 0;
+    current_code     = string_code;
+    *first_char_code = CODE_UNSET;
+
+    while (count < bufsize) {
+        switch (current_code) {
+        case CODE_UNSET:
+            return count;
+            break;
+        default:
+            if (current_code < FIRST_CODE) {
+                *first_char_code = current_code;
+                buff[0] = current_code;
+                count++;
+                return count;
+            } else {
+                offset  = dict[current_code].match_len - 1;
+                tmp_code = dict[current_code].char_code;
+                buff[offset] = tmp_code;
+                count++;
+            }
+            current_code = dict[current_code].parent_code;
+            if ((current_code < 0) || (current_code > (DIC_INDEX_MAX - 1))) {
+                av_log(mlz->context, AV_LOG_ERROR, "MLZ dic index error.\n");
+                return count;
+            }
+            if (current_code > FIRST_CODE) {
+                parent_code = dict[current_code].parent_code;
+                offset = (dict[current_code].match_len) - 1;
+                if (parent_code < 0 || parent_code > DIC_INDEX_MAX-1) {
+                    av_log(mlz->context, AV_LOG_ERROR, "MLZ dic index error.\n");
+                    return count;
+                }
+                if (( offset > (DIC_INDEX_MAX - 1))) {
+                    av_log(mlz->context, AV_LOG_ERROR, "MLZ dic offset error.\n");
+                    return count;
+                }
+            }
+            break;
+        }
+    }
+    return count;
+}
+
+static int input_code(GetBitContext* gb, int len) {
+    int tmp_code = 0;
+    int i;
+    for (i = 0; i < len; ++i) {
+        tmp_code |= get_bits1(gb) << i;
+    }
+    return tmp_code;
+}
+
+int ff_mlz_decompression(MLZ* mlz, GetBitContext* gb, int size, unsigned char *buff) {
+    MLZDict *dict = mlz->dict;
+    unsigned long output_chars;
+    int string_code, last_string_code, char_code;
+
+    string_code = 0;
+    char_code   = -1;
+    last_string_code = -1;
+    output_chars = 0;
+
+    while (output_chars < size) {
+        string_code = input_code(gb, mlz->dic_code_bit);
+        switch (string_code) {
+            case FLUSH_CODE:
+            case MAX_CODE:
+                ff_mlz_flush_dict(mlz);
+                char_code = -1;
+                last_string_code = -1;
+                break;
+            case FREEZE_CODE:
+                mlz->freeze_flag = 1;
+                break;
+            default:
+                if (string_code > mlz->current_dic_index_max) {
+                    av_log(mlz->context, AV_LOG_ERROR, "String code %d exceeds maximum value of %d.\n", string_code, mlz->current_dic_index_max);
+                    return output_chars;
+                }
+                if (string_code == (int) mlz->bump_code) {
+                    ++mlz->dic_code_bit;
+                    mlz->current_dic_index_max *= 2;
+                    mlz->bump_code = mlz->current_dic_index_max - 1;
+                } else {
+                    if (string_code >= mlz->next_code) {
+                        output_chars += decode_string(mlz, &buff[output_chars], last_string_code, &char_code, size - output_chars);
+                        output_chars += decode_string(mlz, &buff[output_chars], char_code, &char_code, size - output_chars);
+                        set_new_entry_dict(dict, mlz->next_code, last_string_code, char_code);
+                        mlz->next_code++;
+                    } else {
+                        output_chars += decode_string(mlz, &buff[output_chars], string_code, &char_code, size - output_chars);
+                        if (output_chars <= size && !mlz->freeze_flag) {
+                            if (last_string_code != -1) {
+                                set_new_entry_dict(dict, mlz->next_code, last_string_code, char_code);
+                                mlz->next_code++;
+                            }
+                        } else {
+                            break;
+                        }
+                    }
+                    last_string_code = string_code;
+                }
+                break;
+        }
+    }
+    return output_chars;
+}

libavcodec/mlz.h

+/*
+ * Copyright (c) 2016 Umair Khan <omerjerk@gmail.com>
+ *
+ * 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
+ */
+
+#ifndef AVCODEC_MLZ_H
+#define AVCODEC_MLZ_H
+
+#include "get_bits.h"
+
+#define CODE_UNSET          -1
+#define CODE_BIT_INIT       9
+#define DIC_INDEX_INIT      512     // 2^9
+#define DIC_INDEX_MAX       32768l  // 2^15
+#define FLUSH_CODE          256
+#define FREEZE_CODE         257
+#define FIRST_CODE          258
+#define MAX_CODE            32767l
+#define TABLE_SIZE          35023l  // TABLE_SIZE must be a prime number
+
+/** Dictionary structure for mlz decompression
+ */
+typedef struct MLZDict {
+    int  string_code;
+    int  parent_code;
+    int  char_code;
+    int  match_len;
+} MLZDict;
+
+/** MLZ data strucure
+ */
+typedef struct MLZ {
+    int dic_code_bit;
+    int current_dic_index_max;
+    unsigned int bump_code;
+    unsigned int flush_code;
+    int next_code;
+    int freeze_flag;
+    MLZDict* dict;
+    void* context;
+} MLZ;
+
+/** Initialize the dictionary
+ */
+void ff_mlz_init_dict(void* context, MLZ *mlz);
+
+/** Flush the dictionary
+ */
+void ff_mlz_flush_dict(MLZ *dict);
+
+/** Run mlz decompression on the next size bits and the output will be stored in buff
+ */
+int ff_mlz_decompression(MLZ* mlz, GetBitContext* gb, int size, unsigned char *buff);
+
+#endif /*AVCODEC_MLZ_H*/