tailieunhanh - A Concise Introduction to Data Compression- P3

Tham khảo tài liệu 'a concise introduction to data compression- p3', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Deflate Zip and Gzip 111 1 2 or 3 respectively. Notice that a block of compressed data does not always end on a byte boundary. The information in the block is sufficient for the decoder to read all the bits of the compressed block and recognize the end of the block. The 3-bit header of the next block immediately follows the current block and may therefore be located at any position in a byte on the compressed file. The format of a block in mode 1 is as follows 1. The 3-bit header 000 or 100. 2. The rest of the current byte is skipped and the next four bytes contain LEN and the one s complement of LEN as unsigned 16-bit numbers where LEN is the number of data bytes in the block. This is why the block size in this mode is limited to 65 535 bytes. 3. LEN data bytes. The format of a block in mode 2 is different 1. The 3-bit header 001 or 101. 2. This is immediately followed by the fixed prefix codes for literals lengths and the special prefix codes of the distances. 3. Code 256 rather its prefix code designating the end of the block. Code Extra bits Lengths Code Extra bits Lengths Code Extra bits Lengths 257 0 3 267 1 15 16 277 4 67-82 258 0 4 268 1 17 18 278 4 83-98 259 0 5 269 2 19-22 279 4 99-114 260 0 6 270 2 23-26 280 4 115-130 261 0 7 271 2 27-30 281 5 131-162 262 0 8 272 2 31-34 282 5 163-194 263 0 9 273 3 35-42 283 5 195-226 264 0 10 274 3 43-50 284 5 227-257 265 1 11 12 275 3 51-58 285 0 258 266 1 13 14 276 3 59-66 Table Literal Length Edocs for Mode 2. Edoc Bits Prefix codes 0-143 8 00110000-10111111 144-255 9 110010000-111111111 256-279 7 0000000-0010111 280-287 8 11000000-11000111 Table Huffman Codes for Edocs in Mode 2. Mode 2 uses two code tables one for literals and lengths and the other for distances. The codes of the first table are not what is actually written on the compressed file so in Please purchase PDF Split-Merge on to remove this watermark. 112 3. Dictionary Methods order to remove ambiguity the term edoc is used .