Implement task 2.1 fixed Hufmann decode

inflate.c

+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <math.h>
+
+/* Types of huffman codes */ 
+static const int FIXED = 1; 
+static const int DYNAMIC = 2; 
+
+/* Fixed Huffman codes mapping. */ 
+
+static const int DECODE_7_MIN = 0; 
+static const int DECODE_7_MAX = 23;
+static const int DECODE_7[] = {
+    256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269, 270, 
+    271, 272, 273, 274, 275, 276, 277, 278, 279
+};
+
+static const int DECODE_8_MIN = 48;
+static const int DECODE_8_MAX = 191;
+static const int DECODE_8[] = {
+    0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 
+    20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37,
+    38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55,
+    56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73,
+    74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91,
+    92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 
+    108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121,
+    122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 
+    136, 137, 138, 139, 140, 141, 142, 143, 280, 281, 282, 283, 284, 285, 
+    286, 287
+}; 
+
+static const int DECODE_9_MIN = 400;
+static const int DECODE_9_MAX = 511;
+static const int DECODE_9[] = {
+    144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158,
+    159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 
+    174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 
+    189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 
+    204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 
+    219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 
+    234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 
+    249, 250, 251, 252, 253, 254, 255
+};
+
+static const int LENGTH_OFFSET = 257; 
+static const int DECODE_LENGTH[] = {
+    3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, 19, 23, 27, 31, 35, 43, 51, 59, 
+    67, 83, 99, 115, 131, 163, 195, 227, 258
+};
+static const int ADD_LENGTHS[] = {
+    0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2,
+    3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 0
+};
+
+static const int DECODE_DIST[] = {
+    1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, 65, 97, 129, 193,
+    257, 385, 513, 769, 1025, 1537, 2049, 3073, 4097, 6145, 
+    8193, 12289, 16385, 24577
+};
+static const int ADD_DISTS[] = {
+    0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 
+    11, 11, 12, 12, 13, 13
+};
+
+int match(int chunk, const int decode_table[], 
+          const int decode_min, const int decode_max) {
+
+    if (chunk < decode_min || chunk > decode_max) {
+        return -1;
+    }
+
+    return decode_table[chunk - decode_min];
+}
+
+int get_next_bit(char *buf, int n) {
+    int buf_pos = n / 8;
+    int pos = n - 8 * buf_pos; 
+
+    char byte = buf[buf_pos];
+    char mask = 1 << pos;
+    return ((byte & mask) != 0);
+}
+
+/* Read the block starting at the n-th bit */ 
+int read_block(char *buf, int buf_size, int n, FILE *out) {
+    /* First bit is the BFINAL flag */ 
+    bool bfinal = get_next_bit(buf, n);
+
+    /* Next two bits are BTYPE */ 
+    int btype = get_next_bit(buf, n + 1) + 2 * get_next_bit(buf, n + 2);
+
+    int n_read = 3;
+
+    if (btype == DYNAMIC) {  
+        /* TODO */
+    }
+
+    int chunk_val;
+
+    do 
+    {
+        int chunk = 0;
+        /* Read first 7 bytes */ 
+        for (int i = 0; i < 7; i++) {
+            chunk += get_next_bit(buf, n + n_read) << (6 - i);
+            n_read += 1; 
+        }
+        
+        chunk_val = match(chunk, DECODE_7, DECODE_7_MIN, DECODE_7_MAX);
+
+        /* No match, read another bit */ 
+        if (chunk_val == -1) {
+            chunk <<= 1;
+            chunk += get_next_bit(buf, n + n_read);
+            n_read += 1; 
+            chunk_val = match(chunk, DECODE_8, DECODE_8_MIN, DECODE_8_MAX);
+        }
+
+        /* Again no match, read another bit */ 
+        if (chunk_val == -1) {
+            chunk += get_next_bit(buf, n + n_read);
+            n_read += 1; 
+            chunk_val = match(chunk, DECODE_9, DECODE_9_MIN, DECODE_9_MAX);
+        }
+        /* Literal */ 
+        if (chunk_val <= 255) {
+            fwrite(&chunk_val, 1, sizeof(char), out);
+        }
+        /* Length */ 
+        else if (chunk_val != 256) {
+            int length = DECODE_LENGTH[chunk_val - LENGTH_OFFSET];
+            /* Might need to read some extra bits and add to the length */ 
+            int additional_bits = ADD_LENGTHS[chunk_val - LENGTH_OFFSET]; 
+            for (int i = 0; i < additional_bits; i++) { 
+                length += get_next_bit(buf, n + n_read) << i;
+                n_read += 1;
+            }
+
+            /* Next 5 bits are a distance */ 
+            int dist_val = 0;
+            for (int i = 0; i < 5; i++) { 
+                dist_val += get_next_bit(buf, n + n_read) << (4 - i); 
+                n_read += 1; 
+            }
+            int dist = DECODE_DIST[dist_val];
+            additional_bits = ADD_DISTS[dist_val]; 
+            for (int i = 0; i < additional_bits; i++) {
+                dist += get_next_bit(buf, n + n_read) << i;
+                n_read += 1;
+            }
+
+            for (int i = 0; i < length; i++) {
+                fseek(out, -dist, SEEK_CUR);
+                int c = fgetc(out);
+                fseek(out, 0, SEEK_END);
+                fwrite(&c, 1, sizeof(char), out); 
+            }
+        }
+    }
+    while (chunk_val != 256);
+
+    return n_read;
+}
+
+void inflate(FILE *fp) { 
+    /* Create output file */
+    FILE *out = fopen("test.txt", "wb+");
+    
+    /* Read the file into a buffer */  
+    fseek(fp, 0, SEEK_END);
+    long size = ftell(fp);
+    rewind(fp);
+    char *buf = (char *) malloc(size);
+    if (!buf) {
+        fprintf(stderr, "error: memory error\n");
+        exit(1);
+    } 
+    fread(buf, 1, size, fp);
+
+    long n_read = 0;
+
+    while (n_read < 8 * size) {
+        n_read += read_block(buf, size, n_read, out); 
+        break;
+    } 
+    
+    fclose(out);
+    free(buf);
+}
+
+int main(int argc, char *argv[]) { 
+    if (argc != 2) {
+        fprintf(stderr, "usage: inflate [file]\n");
+        return 1;
+    }
+    
+    char *fname = argv[1];
+
+    FILE *fp = fopen(fname, "rb");
+    
+    if (!fp) {
+        fprintf(stderr, "error: file not found\n");
+        return 1;
+    }
+
+    inflate(fp);
+
+    fclose(fp);
+    return 0;
+}