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486 lines
13 KiB
486 lines
13 KiB
/* deflate.c - deflate/inflate code for gzip and friends
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*
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* Copyright 2014 Rob Landley <rob@landley.net>
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*
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* See RFCs 1950 (zlib), 1951 (deflate), and 1952 (gzip)
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* LSB 4.1 has gzip, gunzip, and zcat
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*
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* TODO: zip -d DIR -x LIST -list -quiet -no overwrite -overwrite -p to stdout
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*/
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#include "toys.h"
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struct deflate {
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// Huffman codes: base offset and extra bits tables (length and distance)
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char lenbits[29], distbits[30];
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unsigned short lenbase[29], distbase[30];
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void *fixdisthuff, *fixlithuff;
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// CRC
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void (*crcfunc)(struct deflate *dd, char *data, int len);
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unsigned crctable[256], crc;
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// Tables only used for deflation
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unsigned short *hashhead, *hashchain;
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// Compressed data buffer (extra space malloced at end)
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unsigned pos, len;
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int infd, outfd;
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char data[];
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};
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// little endian bit buffer
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struct bitbuf {
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int fd, bitpos, len, max;
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char buf[];
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};
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// malloc a struct bitbuf
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static struct bitbuf *bitbuf_init(int fd, int size)
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{
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struct bitbuf *bb = xzalloc(sizeof(struct bitbuf)+size);
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bb->max = size;
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bb->fd = fd;
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return bb;
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}
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// Advance bitpos without the overhead of recording bits
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// Loads more data when input buffer empty
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static void bitbuf_skip(struct bitbuf *bb, int bits)
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{
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int pos = bb->bitpos + bits, len = bb->len << 3;
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while (pos >= len) {
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pos -= len;
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len = (bb->len = read(bb->fd, bb->buf, bb->max)) << 3;
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if (bb->len < 1) perror_exit("inflate EOF");
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}
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bb->bitpos = pos;
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}
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// Optimized single bit inlined version
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static inline int bitbuf_bit(struct bitbuf *bb)
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{
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int bufpos = bb->bitpos>>3;
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if (bufpos == bb->len) {
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bitbuf_skip(bb, 0);
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bufpos = 0;
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}
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return (bb->buf[bufpos]>>(bb->bitpos++&7))&1;
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}
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// Fetch the next X bits from the bitbuf, little endian
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static unsigned bitbuf_get(struct bitbuf *bb, int bits)
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{
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int result = 0, offset = 0;
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while (bits) {
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int click = bb->bitpos >> 3, blow, blen;
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// Load more data if buffer empty
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if (click == bb->len) bitbuf_skip(bb, click = 0);
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// grab bits from next byte
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blow = bb->bitpos & 7;
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blen = 8-blow;
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if (blen > bits) blen = bits;
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result |= ((bb->buf[click] >> blow) & ((1<<blen)-1)) << offset;
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offset += blen;
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bits -= blen;
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bb->bitpos += blen;
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}
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return result;
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}
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static void bitbuf_flush(struct bitbuf *bb)
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{
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if (!bb->bitpos) return;
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xwrite(bb->fd, bb->buf, (bb->bitpos+7)>>3);
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memset(bb->buf, 0, bb->max);
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bb->bitpos = 0;
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}
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static void bitbuf_put(struct bitbuf *bb, int data, int len)
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{
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while (len) {
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int click = bb->bitpos >> 3, blow, blen;
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// Flush buffer if necessary
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if (click == bb->max) {
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bitbuf_flush(bb);
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click = 0;
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}
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blow = bb->bitpos & 7;
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blen = 8-blow;
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if (blen > len) blen = len;
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bb->buf[click] |= data << blow;
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bb->bitpos += blen;
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data >>= blen;
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len -= blen;
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}
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}
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static void output_byte(struct deflate *dd, char sym)
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{
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int pos = dd->pos++ & 32767;
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dd->data[pos] = sym;
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if (pos == 32767) {
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xwrite(dd->outfd, dd->data, 32768);
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if (dd->crcfunc) dd->crcfunc(dd, dd->data, 32768);
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}
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}
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// Huffman coding uses bits to traverse a binary tree to a leaf node,
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// By placing frequently occurring symbols at shorter paths, frequently
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// used symbols may be represented in fewer bits than uncommon symbols.
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// (length[0] isn't used but code's clearer if it's there.)
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struct huff {
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unsigned short length[16]; // How many symbols have this bit length?
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unsigned short symbol[288]; // sorted by bit length, then ascending order
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};
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// Create simple huffman tree from array of bit lengths.
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// The symbols in the huffman trees are sorted (first by bit length
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// of the code to reach them, then by symbol number). This means that given
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// the bit length of each symbol, we can construct a unique tree.
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static void len2huff(struct huff *huff, char bitlen[], int len)
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{
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int offset[16];
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int i;
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// Count number of codes at each bit length
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memset(huff, 0, sizeof(struct huff));
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for (i = 0; i<len; i++) huff->length[bitlen[i]]++;
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// Sort symbols by bit length, then symbol. Get list of starting positions
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// for each group, then write each symbol to next position within its group.
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*huff->length = *offset = 0;
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for (i = 1; i<16; i++) offset[i] = offset[i-1] + huff->length[i-1];
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for (i = 0; i<len; i++) if (bitlen[i]) huff->symbol[offset[bitlen[i]]++] = i;
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}
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// Fetch and decode next huffman coded symbol from bitbuf.
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// This takes advantage of the sorting to navigate the tree as an array:
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// each time we fetch a bit we have all the codes at that bit level in
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// order with no gaps.
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static unsigned huff_and_puff(struct bitbuf *bb, struct huff *huff)
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{
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unsigned short *length = huff->length;
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int start = 0, offset = 0;
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// Traverse through the bit lengths until our code is in this range
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for (;;) {
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offset = (offset << 1) | bitbuf_bit(bb);
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start += *++length;
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if ((offset -= *length) < 0) break;
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if ((length - huff->length) & 16) error_exit("bad symbol");
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}
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return huff->symbol[start + offset];
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}
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// Decompress deflated data from bitbuf to dd->outfd.
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static void inflate(struct deflate *dd, struct bitbuf *bb)
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{
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dd->crc = ~0;
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// repeat until spanked
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for (;;) {
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int final, type;
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final = bitbuf_get(bb, 1);
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type = bitbuf_get(bb, 2);
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if (type == 3) error_exit("bad type");
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// Uncompressed block?
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if (!type) {
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int len, nlen;
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// Align to byte, read length
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bitbuf_skip(bb, (8-bb->bitpos)&7);
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len = bitbuf_get(bb, 16);
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nlen = bitbuf_get(bb, 16);
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if (len != (0xffff & ~nlen)) error_exit("bad len");
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// Dump literal output data
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while (len) {
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int pos = bb->bitpos >> 3, bblen = bb->len - pos;
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char *p = bb->buf+pos;
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// dump bytes until done or end of current bitbuf contents
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if (bblen > len) bblen = len;
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pos = bblen;
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while (pos--) output_byte(dd, *(p++));
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bitbuf_skip(bb, bblen << 3);
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len -= bblen;
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}
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// Compressed block
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} else {
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struct huff *disthuff, *lithuff;
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// Dynamic huffman codes?
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if (type == 2) {
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struct huff *h2 = ((struct huff *)libbuf)+1;
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int i, litlen, distlen, hufflen;
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char *hufflen_order = "\x10\x11\x12\0\x08\x07\x09\x06\x0a\x05\x0b"
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"\x04\x0c\x03\x0d\x02\x0e\x01\x0f", *bits;
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// The huffman trees are stored as a series of bit lengths
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litlen = bitbuf_get(bb, 5)+257; // max 288
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distlen = bitbuf_get(bb, 5)+1; // max 32
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hufflen = bitbuf_get(bb, 4)+4; // max 19
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// The literal and distance codes are themselves compressed, in
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// a complicated way: an array of bit lengths (hufflen many
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// entries, each 3 bits) is used to fill out an array of 19 entries
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// in a magic order, leaving the rest 0. Then make a tree out of it:
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memset(bits = libbuf+1, 0, 19);
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for (i=0; i<hufflen; i++) bits[hufflen_order[i]] = bitbuf_get(bb, 3);
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len2huff(h2, bits, 19);
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// Use that tree to read in the literal and distance bit lengths
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for (i = 0; i < litlen + distlen;) {
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int sym = huff_and_puff(bb, h2);
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// 0-15 are literals, 16 = repeat previous code 3-6 times,
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// 17 = 3-10 zeroes (3 bit), 18 = 11-138 zeroes (7 bit)
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if (sym < 16) bits[i++] = sym;
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else {
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int len = sym & 2;
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len = bitbuf_get(bb, sym-14+len+(len>>1)) + 3 + (len<<2);
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memset(bits+i, bits[i-1] * !(sym&3), len);
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i += len;
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}
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}
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if (i > litlen+distlen) error_exit("bad tree");
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len2huff(lithuff = h2, bits, litlen);
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len2huff(disthuff = ((struct huff *)libbuf)+2, bits+litlen, distlen);
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// Static huffman codes
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} else {
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lithuff = dd->fixlithuff;
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disthuff = dd->fixdisthuff;
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}
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// Use huffman tables to decode block of compressed symbols
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for (;;) {
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int sym = huff_and_puff(bb, lithuff);
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// Literal?
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if (sym < 256) output_byte(dd, sym);
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// Copy range?
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else if (sym > 256) {
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int len, dist;
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sym -= 257;
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len = dd->lenbase[sym] + bitbuf_get(bb, dd->lenbits[sym]);
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sym = huff_and_puff(bb, disthuff);
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dist = dd->distbase[sym] + bitbuf_get(bb, dd->distbits[sym]);
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sym = dd->pos & 32767;
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while (len--) output_byte(dd, dd->data[(dd->pos-dist) & 32767]);
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// End of block
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} else break;
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}
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}
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// Was that the last block?
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if (final) break;
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}
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if (dd->pos & 32767) {
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xwrite(dd->outfd, dd->data, dd->pos&32767);
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if (dd->crcfunc) dd->crcfunc(dd, dd->data, dd->pos&32767);
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}
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}
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// Deflate from dd->infd to bitbuf
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// For deflate, dd->len = input read, dd->pos = input consumed
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static void deflate(struct deflate *dd, struct bitbuf *bb)
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{
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char *data = dd->data;
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int len, final = 0;
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dd->crc = ~0;
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while (!final) {
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// Read next half-window of data if we haven't hit EOF yet.
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len = readall(dd->infd, data+(dd->len&32768), 32768);
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if (len < 0) perror_exit("read"); // todo: add filename
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if (len != 32768) final++;
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if (dd->crcfunc) dd->crcfunc(dd, data+(dd->len&32768), len);
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// dd->len += len; crcfunc advances len TODO
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// store block as literal
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bitbuf_put(bb, final, 1);
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bitbuf_put(bb, 0, 1);
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bitbuf_put(bb, 0, (8-bb->bitpos)&7);
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bitbuf_put(bb, len, 16);
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bitbuf_put(bb, 0xffff & ~len, 16);
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// repeat until spanked
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while (dd->pos != dd->len) {
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unsigned pos = dd->pos&65535;
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bitbuf_put(bb, data[pos], 8);
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// need to refill buffer?
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if (!(32767 & ++dd->pos) && !final) break;
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}
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}
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bitbuf_flush(bb);
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}
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// Allocate memory for deflate/inflate.
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static struct deflate *init_deflate(int compress)
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{
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int i, n = 1;
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struct deflate *dd = xmalloc(sizeof(struct deflate)+32768*(compress ? 4 : 1));
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memset(dd, 0, sizeof(struct deflate));
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// decompress needs 32k history, compress adds 64k hashhead and 32k hashchain
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if (compress) {
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dd->hashhead = (unsigned short *)(dd->data+65536);
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dd->hashchain = (unsigned short *)(dd->data+65536+32768);
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}
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// Calculate lenbits, lenbase, distbits, distbase
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*dd->lenbase = 3;
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for (i = 0; i<sizeof(dd->lenbits)-1; i++) {
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if (i>4) {
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if (!(i&3)) {
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dd->lenbits[i]++;
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n <<= 1;
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}
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if (i == 27) n--;
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else dd->lenbits[i+1] = dd->lenbits[i];
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}
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dd->lenbase[i+1] = n + dd->lenbase[i];
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}
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n = 0;
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for (i = 0; i<sizeof(dd->distbits); i++) {
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dd->distbase[i] = 1<<n;
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if (i) dd->distbase[i] += dd->distbase[i-1];
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if (i>3 && !(i&1)) n++;
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dd->distbits[i] = n;
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}
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// TODO layout and lifetime of this?
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// Init fixed huffman tables
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for (i=0; i<288; i++) libbuf[i] = 8 + (i>143) - ((i>255)<<1) + (i>279);
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len2huff(dd->fixlithuff = ((struct huff *)libbuf)+3, libbuf, 288);
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memset(libbuf, 5, 30);
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len2huff(dd->fixdisthuff = ((struct huff *)libbuf)+4, libbuf, 30);
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return dd;
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}
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// Return true/false whether we consumed a gzip header.
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static int is_gzip(struct bitbuf *bb)
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{
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int flags;
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// Confirm signature
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if (bitbuf_get(bb, 24) != 0x088b1f || (flags = bitbuf_get(bb, 8)) > 31)
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return 0;
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bitbuf_skip(bb, 6*8);
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// Skip extra, name, comment, header CRC fields
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if (flags & 4) bitbuf_skip(bb, bitbuf_get(bb, 16) * 8);
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if (flags & 8) while (bitbuf_get(bb, 8));
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if (flags & 16) while (bitbuf_get(bb, 8));
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if (flags & 2) bitbuf_skip(bb, 16);
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return 1;
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}
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static void gzip_crc(struct deflate *dd, char *data, int len)
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{
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int i;
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unsigned crc, *crc_table = dd->crctable;
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crc = dd->crc;
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for (i=0; i<len; i++) crc = crc_table[(crc^data[i])&0xff] ^ (crc>>8);
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dd->crc = crc;
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dd->len += len;
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}
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long long gzip_fd(int infd, int outfd)
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{
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struct bitbuf *bb = bitbuf_init(outfd, 4096);
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struct deflate *dd = init_deflate(1);
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long long rc;
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// Header from RFC 1952 section 2.2:
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// 2 ID bytes (1F, 8b), gzip method byte (8=deflate), FLAG byte (none),
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// 4 byte MTIME (zeroed), Extra Flags (2=maximum compression),
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// Operating System (FF=unknown)
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dd->infd = infd;
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xwrite(bb->fd, "\x1f\x8b\x08\0\0\0\0\0\x02\xff", 10);
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// Little endian crc table
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crc_init(dd->crctable, 1);
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dd->crcfunc = gzip_crc;
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deflate(dd, bb);
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// tail: crc32, len32
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bitbuf_put(bb, 0, (8-bb->bitpos)&7);
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bitbuf_put(bb, ~dd->crc, 32);
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bitbuf_put(bb, dd->len, 32);
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rc = dd->len;
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bitbuf_flush(bb);
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free(bb);
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free(dd);
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return rc;
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}
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long long gunzip_fd(int infd, int outfd)
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{
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struct bitbuf *bb = bitbuf_init(infd, 4096);
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struct deflate *dd = init_deflate(0);
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long long rc;
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if (!is_gzip(bb)) error_exit("not gzip");
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dd->outfd = outfd;
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// Little endian crc table
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crc_init(dd->crctable, 1);
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dd->crcfunc = gzip_crc;
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inflate(dd, bb);
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// tail: crc32, len32
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bitbuf_skip(bb, (8-bb->bitpos)&7);
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if (~dd->crc != bitbuf_get(bb, 32) || dd->len != bitbuf_get(bb, 32))
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error_exit("bad crc");
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rc = dd->len;
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free(bb);
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free(dd);
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return rc;
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}
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