Mercurial > hg > toybox
view toys/pending/compress.c @ 1200:de10c8142fce draft
Not buying it, eh?
author | Rob Landley <rob@landley.net> |
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date | Mon, 10 Feb 2014 08:30:05 -0600 |
parents | ff8d73e78089 |
children | 9adf66c7dd4e |
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/* compress.c - deflate/inflate code for zip, gzip, zlib, and raw * * Copyright 2014 Rob Landley <rob@landley.net> * * The inflate/deflate code lives here, so the various things that use it * either live here or call these commands to pipe data through them. * * Divergence from posix: replace obsolete "compress" with mutiplexer. * * See RFCs 1950 (zlib), 1951 (deflate), and 1952 (gzip) * LSB 4.1 has gzip, gunzip, and zcat * TODO: zip -d DIR -x LIST -list -quiet -no overwrite -overwrite -p to stdout // Accept many different kinds of command line argument: USE_COMPRESS(NEWTOY(compress, "zglrcd9[-cd][!zglr]", TOYFLAG_USR|TOYFLAG_BIN)) //zip unzip gzip gunzip zcat config COMPRESS bool "compress" default n help usage: compress [-zglrcd9] [FILE] Compress or decompress file (or stdin) using "deflate" algorithm. -c compress -d decompress -g gzip -l zlib -r raw (default) -z zip */ #define FOR_compress #include "toys.h" GLOBALS( // base offset and extra bits tables (length and distance) char lenbits[29], distbits[30]; unsigned short lenbase[29], distbase[30]; unsigned (*crc)(char *data, int len); char *outbuf; unsigned outlen; int outfd; ) // little endian bit buffer struct bitbuf { int fd, bitpos, len, max; char buf[]; }; // malloc a struct bitbuf struct bitbuf *bitbuf_init(int fd, int size) { struct bitbuf *bb = xmalloc(sizeof(struct bitbuf)+size); memset(bb, 0, sizeof(struct bitbuf)); bb->max = size; bb->fd = fd; return bb; } // Advance bitpos without the overhead of recording bits void bitbuf_skip(struct bitbuf *bb, int bits) { int pos = bb->bitpos + bits, len = bb->len << 3; while (pos >= len) { pos -= len; len = (bb->len = read(bb->fd, bb->buf, bb->max)) << 3; if (bb->len < 1) perror_exit("inflate EOF"); } bb->bitpos = pos; } // Optimized single bit inlined version static inline int bitbuf_bit(struct bitbuf *bb) { int bufpos = bb->bitpos>>3; if (bufpos == bb->len) { bitbuf_skip(bb, 0); bufpos = 0; } return (bb->buf[bufpos]>>(bb->bitpos++&7))&1; } // Fetch the next X bits from the bitbuf, little endian int bitbuf_get(struct bitbuf *bb, int bits) { int result = 0, offset = 0; while (bits) { int click = bb->bitpos >> 3, blow, blen; // Load more data if buffer empty if (click == bb->len) bitbuf_skip(bb, 0); // grab bits from next byte blow = bb->bitpos & 7; blen = 8-blow; if (blen > bits) blen = bits; result |= ((bb->buf[click] >> blow) & ((1<<blen)-1)) << offset; offset += blen; bits -= blen; bb->bitpos += blen; } return result; } static void outbuf_crc(char *buf, int len) { if (TT.crc) TT.crc(buf, len); xwrite(TT.outfd, buf, len); } // Huffman coding uses bits to traverse a binary tree to a leaf node, // By placing frequently occurring symbols at shorter paths, frequently // used symbols may be represented in fewer bits than uncommon symbols. struct huff { unsigned short length[16]; unsigned short symbol[288]; }; // Create simple huffman tree from array of bit lengths. // The symbols in deflate's huffman trees are sorted (first by bit length // of the code to reach them, then by symbol number). This means that given // the bit length of each symbol, we can construct a unique tree. static void len2huff(struct huff *huff, char bitlen[], int len) { int offset[16]; int i, sum; // Count number of codes at each bit length memset(huff, 0, sizeof(struct huff)); for (i = 0; i<len; i++) huff->length[bitlen[i]]++; // Sort symbols by bit length. (They'll remain sorted by symbol within that.) *huff->length = *offset = 0; for (i = sum = 0; i<16; i++) offset[i] = offset[i-1] + huff->length[i]; for (i = 0; i<len; i++) if (bitlen[i]) huff->symbol[offset[bitlen[i]]++] = i; } // Fetch and decode next huffman coded symbol from bitbuf. // This takes advantage of the the sorting to navigate the tree as an array: // each time we fetch a bit we have all the codes at that bit level in // order with no gaps.. static unsigned huff_and_puff(struct bitbuf *bb, struct huff *huff) { unsigned short *length = huff->length; int start = 0, offset = 0; // Traverse through the bit lengths until our code is in this range for (;;) { offset = (offset << 1) | bitbuf_bit(bb); start += *++length; if ((offset -= *length) < 0) break; // Note to self: what prevents overflow? // If we ensure ranges add up to sizeof(symbol), does that ensure all codes // terminate within table? Patholotical is 11111111... // if (length - huff_length > 16) error_exit("bad"); } return huff->symbol[start + offset]; } // Decompress deflated data from bitbuf to filehandle. static void inflate(struct bitbuf *bb) { // repeat until spanked for (;;) { int final, type; final = bitbuf_get(bb, 1); type = bitbuf_get(bb, 2); fprintf(stderr, "final=%d type=%d\n", final, type); if (type == 3) error_exit("bad type"); // no compression? if (!type) { int len, nlen; // Align to byte, read length bitbuf_skip(bb, bb->bitpos & 7); len = bitbuf_get(bb, 16); nlen = bitbuf_get(bb, 16); if (len != (0xffff & ~nlen)) error_exit("bad len"); // Dump output data while (len) { int pos = bb->bitpos >> 3, bblen = bb->len - pos; if (bblen > len) bblen = len; if (bblen) outbuf_crc(bb->buf+pos, bblen); len -= bblen; bitbuf_skip(bb, bblen << 3); } // Compressed block } else { // struct huff huff; // Dynamic huffman codes? if (type == 2) { struct huff hlo; int i, literal, distance, hufflen; char *hufflen_order = "\x10\x11\x12\0\x08\x07\x09\x06\x0a\x05\x0b" "\x04\x0c\x03\x0d\x02\x0e\x01\x0f", *bits; // The huffman trees are stored as a series of bit lengths literal = bitbuf_get(bb, 5)+257; // max 288 distance = bitbuf_get(bb, 5)+1; // max 32 hufflen = bitbuf_get(bb, 4)+4; // max 19 // The literal and distance codes are themselves compressed, in // a complicated way: an array of bit lengths (hufflen many // entries, each 3 bits) is used to fill out an array of 19 entries // in a magic order, leaving the rest 0. Then make a tree out of it: memset(bits = toybuf+1, 0, 19); for (i=0; i<hufflen; i++) bits[hufflen_order[i]] = bitbuf_get(bb, 3); len2huff(&hlo, bits, 19); // Use that tree to read in the literal and distance bit lengths for (i = 0; i < literal + distance; i++) { int sym = huff_and_puff(bb, &hlo); // 0-15 are literals, 16 = repeat previous code 3-6 times, // 17 = 3-10 zeroes, 18 = 11-138 zeroes if (sym < 16) bits[i] = sym; else memset(bits+i, bits[i-1] * !(sym&3), bitbuf_get(bb, (sym-14)+((sym&2)<<2))); } // Static huffman codes } else { } } if (final) return; } } static void init_deflate(void) { int i, n = 1; // Ye olde deflate window TT.outbuf = xmalloc(32768); // Calculate lenbits, lenbase, distbits, distbase *TT.lenbase = 3; for (i = 0; i<sizeof(TT.lenbits)-1; i++) { if (i>4) { if (!(i&3)) { TT.lenbits[i]++; n <<= 1; } if (i == 27) n--; else TT.lenbits[i+1] = TT.lenbits[i]; } TT.lenbase[i+1] = n + TT.lenbase[i]; } n = 0; for (i = 0; i<sizeof(TT.distbits); i++) { TT.distbase[i] = 1<<n; if (i) TT.distbase[i] += TT.distbase[i-1]; if (i>3 && !(i&1)) n++; TT.distbits[i] = n; } } // Return true/false whether we consumed a gzip header. static int is_gzip(struct bitbuf *bb) { int flags; // Confirm signature if (bitbuf_get(bb, 24) != 0x088b1f || (flags = bitbuf_get(bb, 8)) > 31) return 0; bitbuf_skip(bb, 6*8); // Skip extra, name, comment, header CRC fields if (flags & 4) bitbuf_skip(bb, 16); if (flags & 8) while (bitbuf_get(bb, 8)); if (flags & 16) while (bitbuf_get(bb, 8)); if (flags & 2) bitbuf_skip(bb, 16); return 1; } static void do_gzip(int fd, char *name) { struct bitbuf *bb = bitbuf_init(fd, sizeof(toybuf)); if (!is_gzip(bb)) error_exit("not gzip"); TT.outfd = 1; inflate(bb); // tail: crc32, len32 free(bb); } // Parse many different kinds of command line argument: void compress_main(void) { init_deflate(); loopfiles(toys.optargs, do_gzip); }