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authorRob Landley <rob@landley.net>2014-02-07 07:56:46 -0600
committerRob Landley <rob@landley.net>2014-02-07 07:56:46 -0600
commitb6c8a8609fbfcbaf054e254f74974394c8932712 (patch)
tree53408d6bd22402bff0fb3ac736d6e41b7a05cc4a /toys/other
parent5486075caee329fcc5ab7766a8a571fd3a45d363 (diff)
downloadtoybox-b6c8a8609fbfcbaf054e254f74974394c8932712.tar.gz
Move bunzip2 logic from lib into bzcat.
Diffstat (limited to 'toys/other')
-rw-r--r--toys/other/bzcat.c626
1 files changed, 625 insertions, 1 deletions
diff --git a/toys/other/bzcat.c b/toys/other/bzcat.c
index 8266484c..642590d1 100644
--- a/toys/other/bzcat.c
+++ b/toys/other/bzcat.c
@@ -1,6 +1,15 @@
/* bzcat.c - decompress stdin to stdout using bunzip2.
*
- * Copyright 2007 Rob Landley <rob@landley.net>
+ * Copyright 2003, 2007 Rob Landley <rob@landley.net>
+ *
+ * Based on a close reading (but not the actual code) of the original bzip2
+ * decompression code by Julian R Seward (jseward@acm.org), which also
+ * acknowledges contributions by Mike Burrows, David Wheeler, Peter Fenwick,
+ * Alistair Moffat, Radford Neal, Ian H. Witten, Robert Sedgewick, and
+ * Jon L. Bentley.
+ *
+ * No standard.
+
USE_BZCAT(NEWTOY(bzcat, NULL, TOYFLAG_USR|TOYFLAG_BIN))
@@ -15,6 +24,621 @@ config BZCAT
#include "toys.h"
+#define THREADS 1
+
+// Constants for huffman coding
+#define MAX_GROUPS 6
+#define GROUP_SIZE 50 /* 64 would have been more efficient */
+#define MAX_HUFCODE_BITS 20 /* Longest huffman code allowed */
+#define MAX_SYMBOLS 258 /* 256 literals + RUNA + RUNB */
+#define SYMBOL_RUNA 0
+#define SYMBOL_RUNB 1
+
+// Other housekeeping constants
+#define IOBUF_SIZE 4096
+
+// Status return values
+#define RETVAL_LAST_BLOCK (-100)
+#define RETVAL_NOT_BZIP_DATA (-1)
+#define RETVAL_DATA_ERROR (-2)
+#define RETVAL_OBSOLETE_INPUT (-3)
+
+// This is what we know about each huffman coding group
+struct group_data {
+ int limit[MAX_HUFCODE_BITS+1], base[MAX_HUFCODE_BITS], permute[MAX_SYMBOLS];
+ char minLen, maxLen;
+};
+
+// Data for burrows wheeler transform
+
+struct bwdata {
+ unsigned int origPtr;
+ int byteCount[256];
+ // State saved when interrupting output
+ int writePos, writeRun, writeCount, writeCurrent;
+ unsigned int dataCRC, headerCRC;
+ unsigned int *dbuf;
+};
+
+// Structure holding all the housekeeping data, including IO buffers and
+// memory that persists between calls to bunzip
+struct bunzip_data {
+ // Input stream, input buffer, input bit buffer
+ int in_fd, inbufCount, inbufPos;
+ char *inbuf;
+ unsigned int inbufBitCount, inbufBits;
+
+ // Output buffer
+ char outbuf[IOBUF_SIZE];
+ int outbufPos;
+
+ unsigned int totalCRC;
+
+ // First pass decompression data (Huffman and MTF decoding)
+ char selectors[32768]; // nSelectors=15 bits
+ struct group_data groups[MAX_GROUPS]; // huffman coding tables
+ int symTotal, groupCount, nSelectors;
+ unsigned char symToByte[256], mtfSymbol[256];
+
+ // The CRC values stored in the block header and calculated from the data
+ unsigned int crc32Table[256];
+
+ // Second pass decompression data (burrows-wheeler transform)
+ unsigned int dbufSize;
+ struct bwdata bwdata[THREADS];
+};
+
+// Return the next nnn bits of input. All reads from the compressed input
+// are done through this function. All reads are big endian.
+static unsigned int get_bits(struct bunzip_data *bd, char bits_wanted)
+{
+ unsigned int bits = 0;
+
+ // If we need to get more data from the byte buffer, do so. (Loop getting
+ // one byte at a time to enforce endianness and avoid unaligned access.)
+ while (bd->inbufBitCount < bits_wanted) {
+
+ // If we need to read more data from file into byte buffer, do so
+ if (bd->inbufPos == bd->inbufCount) {
+ if (0 >= (bd->inbufCount = read(bd->in_fd, bd->inbuf, IOBUF_SIZE)))
+ error_exit("input EOF");
+ bd->inbufPos = 0;
+ }
+
+ // Avoid 32-bit overflow (dump bit buffer to top of output)
+ if (bd->inbufBitCount>=24) {
+ bits = bd->inbufBits&((1<<bd->inbufBitCount)-1);
+ bits_wanted -= bd->inbufBitCount;
+ bits <<= bits_wanted;
+ bd->inbufBitCount = 0;
+ }
+
+ // Grab next 8 bits of input from buffer.
+ bd->inbufBits = (bd->inbufBits<<8) | bd->inbuf[bd->inbufPos++];
+ bd->inbufBitCount += 8;
+ }
+
+ // Calculate result
+ bd->inbufBitCount -= bits_wanted;
+ bits |= (bd->inbufBits>>bd->inbufBitCount) & ((1<<bits_wanted)-1);
+
+ return bits;
+}
+
+/* Read block header at start of a new compressed data block. Consists of:
+ *
+ * 48 bits : Block signature, either pi (data block) or e (EOF block).
+ * 32 bits : bw->headerCRC
+ * 1 bit : obsolete feature flag.
+ * 24 bits : origPtr (Burrows-wheeler unwind index, only 20 bits ever used)
+ * 16 bits : Mapping table index.
+ *[16 bits]: symToByte[symTotal] (Mapping table. For each bit set in mapping
+ * table index above, read another 16 bits of mapping table data.
+ * If correspondig bit is unset, all bits in that mapping table
+ * section are 0.)
+ * 3 bits : groupCount (how many huffman tables used to encode, anywhere
+ * from 2 to MAX_GROUPS)
+ * variable: hufGroup[groupCount] (MTF encoded huffman table data.)
+ */
+
+static int read_block_header(struct bunzip_data *bd, struct bwdata *bw)
+{
+ struct group_data *hufGroup;
+ int hh, ii, jj, kk, symCount, *base, *limit;
+ unsigned char uc;
+
+ // Read in header signature and CRC (which is stored big endian)
+ ii = get_bits(bd, 24);
+ jj = get_bits(bd, 24);
+ bw->headerCRC = get_bits(bd,32);
+
+ // Is this the EOF block with CRC for whole file? (Constant is "e")
+ if (ii==0x177245 && jj==0x385090) return RETVAL_LAST_BLOCK;
+
+ // Is this a valid data block? (Constant is "pi".)
+ if (ii!=0x314159 || jj!=0x265359) return RETVAL_NOT_BZIP_DATA;
+
+ // We can add support for blockRandomised if anybody complains.
+ if (get_bits(bd,1)) return RETVAL_OBSOLETE_INPUT;
+ if ((bw->origPtr = get_bits(bd,24)) > bd->dbufSize) return RETVAL_DATA_ERROR;
+
+ // mapping table: if some byte values are never used (encoding things
+ // like ascii text), the compression code removes the gaps to have fewer
+ // symbols to deal with, and writes a sparse bitfield indicating which
+ // values were present. We make a translation table to convert the symbols
+ // back to the corresponding bytes.
+ hh = get_bits(bd, 16);
+ bd->symTotal = 0;
+ for (ii=0; ii<16; ii++) {
+ if (hh & (1 << (15 - ii))) {
+ kk = get_bits(bd, 16);
+ for (jj=0; jj<16; jj++)
+ if (kk & (1 << (15 - jj)))
+ bd->symToByte[bd->symTotal++] = (16 * ii) + jj;
+ }
+ }
+
+ // How many different huffman coding groups does this block use?
+ bd->groupCount = get_bits(bd,3);
+ if (bd->groupCount<2 || bd->groupCount>MAX_GROUPS) return RETVAL_DATA_ERROR;
+
+ // nSelectors: Every GROUP_SIZE many symbols we switch huffman coding
+ // tables. Each group has a selector, which is an index into the huffman
+ // coding table arrays.
+ //
+ // Read in the group selector array, which is stored as MTF encoded
+ // bit runs. (MTF = Move To Front. Every time a symbol occurs it's moved
+ // to the front of the table, so it has a shorter encoding next time.)
+ if (!(bd->nSelectors = get_bits(bd, 15))) return RETVAL_DATA_ERROR;
+ for (ii=0; ii<bd->groupCount; ii++) bd->mtfSymbol[ii] = ii;
+ for (ii=0; ii<bd->nSelectors; ii++) {
+
+ // Get next value
+ for(jj=0;get_bits(bd,1);jj++)
+ if (jj>=bd->groupCount) return RETVAL_DATA_ERROR;
+
+ // Decode MTF to get the next selector, and move it to the front.
+ uc = bd->mtfSymbol[jj];
+ memmove(bd->mtfSymbol+1, bd->mtfSymbol, jj);
+ bd->mtfSymbol[0] = bd->selectors[ii] = uc;
+ }
+
+ // Read the huffman coding tables for each group, which code for symTotal
+ // literal symbols, plus two run symbols (RUNA, RUNB)
+ symCount = bd->symTotal+2;
+ for (jj=0; jj<bd->groupCount; jj++) {
+ unsigned char length[MAX_SYMBOLS];
+ unsigned temp[MAX_HUFCODE_BITS+1];
+ int minLen, maxLen, pp;
+
+ // Read lengths
+ hh = get_bits(bd, 5);
+ for (ii = 0; ii < symCount; ii++) {
+ for(;;) {
+ // !hh || hh > MAX_HUFCODE_BITS in one test.
+ if (MAX_HUFCODE_BITS-1 < (unsigned)hh-1) return RETVAL_DATA_ERROR;
+ // Grab 2 bits instead of 1 (slightly smaller/faster). Stop if
+ // first bit is 0, otherwise second bit says whether to
+ // increment or decrement.
+ kk = get_bits(bd, 2);
+ if (kk & 2) hh += 1 - ((kk&1)<<1);
+ else {
+ bd->inbufBitCount++;
+ break;
+ }
+ }
+ length[ii] = hh;
+ }
+
+ // Find largest and smallest lengths in this group
+ minLen = maxLen = length[0];
+ for (ii = 1; ii < symCount; ii++) {
+ if(length[ii] > maxLen) maxLen = length[ii];
+ else if(length[ii] < minLen) minLen = length[ii];
+ }
+
+ /* Calculate permute[], base[], and limit[] tables from length[].
+ *
+ * permute[] is the lookup table for converting huffman coded symbols
+ * into decoded symbols. It contains symbol values sorted by length.
+ *
+ * base[] is the amount to subtract from the value of a huffman symbol
+ * of a given length when using permute[].
+ *
+ * limit[] indicates the largest numerical value a symbol with a given
+ * number of bits can have. It lets us know when to stop reading.
+ *
+ * To use these, keep reading bits until value <= limit[bitcount] or
+ * you've read over 20 bits (error). Then the decoded symbol
+ * equals permute[hufcode_value - base[hufcode_bitcount]].
+ */
+ hufGroup = bd->groups+jj;
+ hufGroup->minLen = minLen;
+ hufGroup->maxLen = maxLen;
+
+ // Note that minLen can't be smaller than 1, so we adjust the base
+ // and limit array pointers so we're not always wasting the first
+ // entry. We do this again when using them (during symbol decoding).
+ base = hufGroup->base-1;
+ limit = hufGroup->limit-1;
+
+ // zero temp[] and limit[], and calculate permute[]
+ pp = 0;
+ for (ii = minLen; ii <= maxLen; ii++) {
+ temp[ii] = limit[ii] = 0;
+ for (hh = 0; hh < symCount; hh++)
+ if (length[hh] == ii) hufGroup->permute[pp++] = hh;
+ }
+
+ // Count symbols coded for at each bit length
+ for (ii = 0; ii < symCount; ii++) temp[length[ii]]++;
+
+ /* Calculate limit[] (the largest symbol-coding value at each bit
+ * length, which is (previous limit<<1)+symbols at this level), and
+ * base[] (number of symbols to ignore at each bit length, which is
+ * limit minus the cumulative count of symbols coded for already). */
+ pp = hh = 0;
+ for (ii = minLen; ii < maxLen; ii++) {
+ pp += temp[ii];
+ limit[ii] = pp-1;
+ pp <<= 1;
+ base[ii+1] = pp-(hh+=temp[ii]);
+ }
+ limit[maxLen] = pp+temp[maxLen]-1;
+ limit[maxLen+1] = INT_MAX;
+ base[minLen] = 0;
+ }
+
+ return 0;
+}
+
+/* First pass, read block's symbols into dbuf[dbufCount].
+ *
+ * This undoes three types of compression: huffman coding, run length encoding,
+ * and move to front encoding. We have to undo all those to know when we've
+ * read enough input.
+ */
+
+static int read_huffman_data(struct bunzip_data *bd, struct bwdata *bw)
+{
+ struct group_data *hufGroup;
+ int hh, ii, jj, kk, runPos, dbufCount, symCount, selector, nextSym,
+ *byteCount, *base, *limit;
+ unsigned int *dbuf = bw->dbuf;
+ unsigned char uc;
+
+ // We've finished reading and digesting the block header. Now read this
+ // block's huffman coded symbols from the file and undo the huffman coding
+ // and run length encoding, saving the result into dbuf[dbufCount++] = uc
+
+ // Initialize symbol occurrence counters and symbol mtf table
+ byteCount = bw->byteCount;
+ for(ii=0; ii<256; ii++) {
+ byteCount[ii] = 0;
+ bd->mtfSymbol[ii] = ii;
+ }
+
+ // Loop through compressed symbols. This is the first "tight inner loop"
+ // that needs to be micro-optimized for speed. (This one fills out dbuf[]
+ // linearly, staying in cache more, so isn't as limited by DRAM access.)
+ runPos = dbufCount = symCount = selector = 0;
+ // Some unnecessary initializations to shut gcc up.
+ base = limit = 0;
+ hufGroup = 0;
+ hh = 0;
+
+ for (;;) {
+ // Have we reached the end of this huffman group?
+ if (!(symCount--)) {
+ // Determine which huffman coding group to use.
+ symCount = GROUP_SIZE-1;
+ if (selector >= bd->nSelectors) return RETVAL_DATA_ERROR;
+ hufGroup = bd->groups + bd->selectors[selector++];
+ base = hufGroup->base-1;
+ limit = hufGroup->limit-1;
+ }
+
+ // Read next huffman-coded symbol (into jj).
+ ii = hufGroup->minLen;
+ jj = get_bits(bd, ii);
+ while (jj > limit[ii]) {
+ // if (ii > hufGroup->maxLen) return RETVAL_DATA_ERROR;
+ ii++;
+
+ // Unroll get_bits() to avoid a function call when the data's in
+ // the buffer already.
+ kk = bd->inbufBitCount
+ ? (bd->inbufBits >> --(bd->inbufBitCount)) & 1 : get_bits(bd, 1);
+ jj = (jj << 1) | kk;
+ }
+ // Huffman decode jj into nextSym (with bounds checking)
+ jj-=base[ii];
+
+ if (ii > hufGroup->maxLen || (unsigned)jj >= MAX_SYMBOLS)
+ return RETVAL_DATA_ERROR;
+ nextSym = hufGroup->permute[jj];
+
+ // If this is a repeated run, loop collecting data
+ if ((unsigned)nextSym <= SYMBOL_RUNB) {
+ // If this is the start of a new run, zero out counter
+ if(!runPos) {
+ runPos = 1;
+ hh = 0;
+ }
+
+ /* Neat trick that saves 1 symbol: instead of or-ing 0 or 1 at
+ each bit position, add 1 or 2 instead. For example,
+ 1011 is 1<<0 + 1<<1 + 2<<2. 1010 is 2<<0 + 2<<1 + 1<<2.
+ You can make any bit pattern that way using 1 less symbol than
+ the basic or 0/1 method (except all bits 0, which would use no
+ symbols, but a run of length 0 doesn't mean anything in this
+ context). Thus space is saved. */
+ hh += (runPos << nextSym); // +runPos if RUNA; +2*runPos if RUNB
+ runPos <<= 1;
+ continue;
+ }
+
+ /* When we hit the first non-run symbol after a run, we now know
+ how many times to repeat the last literal, so append that many
+ copies to our buffer of decoded symbols (dbuf) now. (The last
+ literal used is the one at the head of the mtfSymbol array.) */
+ if (runPos) {
+ runPos = 0;
+ if (dbufCount+hh > bd->dbufSize) return RETVAL_DATA_ERROR;
+
+ uc = bd->symToByte[bd->mtfSymbol[0]];
+ byteCount[uc] += hh;
+ while (hh--) dbuf[dbufCount++] = uc;
+ }
+
+ // Is this the terminating symbol?
+ if (nextSym>bd->symTotal) break;
+
+ /* At this point, the symbol we just decoded indicates a new literal
+ character. Subtract one to get the position in the MTF array
+ at which this literal is currently to be found. (Note that the
+ result can't be -1 or 0, because 0 and 1 are RUNA and RUNB.
+ Another instance of the first symbol in the mtf array, position 0,
+ would have been handled as part of a run.) */
+ if (dbufCount>=bd->dbufSize) return RETVAL_DATA_ERROR;
+ ii = nextSym - 1;
+ uc = bd->mtfSymbol[ii];
+ // On my laptop, unrolling this memmove() into a loop shaves 3.5% off
+ // the total running time.
+ while(ii--) bd->mtfSymbol[ii+1] = bd->mtfSymbol[ii];
+ bd->mtfSymbol[0] = uc;
+ uc = bd->symToByte[uc];
+
+ // We have our literal byte. Save it into dbuf.
+ byteCount[uc]++;
+ dbuf[dbufCount++] = (unsigned int)uc;
+ }
+
+ // Now we know what dbufCount is, do a better sanity check on origPtr.
+ if (bw->origPtr >= (bw->writeCount = dbufCount)) return RETVAL_DATA_ERROR;
+
+ return 0;
+}
+
+// Flush output buffer to disk
+void flush_bunzip_outbuf(struct bunzip_data *bd, int out_fd)
+{
+ if (bd->outbufPos) {
+ if (write(out_fd, bd->outbuf, bd->outbufPos) != bd->outbufPos)
+ error_exit("output EOF");
+ bd->outbufPos = 0;
+ }
+}
+
+void burrows_wheeler_prep(struct bunzip_data *bd, struct bwdata *bw)
+{
+ int ii, jj;
+ unsigned int *dbuf = bw->dbuf;
+ int *byteCount = bw->byteCount;
+
+ // Technically this part is preparation for the burrows-wheeler
+ // transform, but it's quick and convenient to do here.
+
+ // Turn byteCount into cumulative occurrence counts of 0 to n-1.
+ jj = 0;
+ for (ii=0; ii<256; ii++) {
+ int kk = jj + byteCount[ii];
+ byteCount[ii] = jj;
+ jj = kk;
+ }
+
+ // Use occurrence counts to quickly figure out what order dbuf would be in
+ // if we sorted it.
+ for (ii=0; ii < bw->writeCount; ii++) {
+ unsigned char uc = dbuf[ii];
+ dbuf[byteCount[uc]] |= (ii << 8);
+ byteCount[uc]++;
+ }
+
+ // blockRandomised support would go here.
+
+ // Using ii as position, jj as previous character, hh as current character,
+ // and uc as run count.
+ bw->dataCRC = 0xffffffffL;
+
+ /* Decode first byte by hand to initialize "previous" byte. Note that it
+ doesn't get output, and if the first three characters are identical
+ it doesn't qualify as a run (hence uc=255, which will either wrap
+ to 1 or get reset). */
+ if (bw->writeCount) {
+ bw->writePos = dbuf[bw->origPtr];
+ bw->writeCurrent = (unsigned char)bw->writePos;
+ bw->writePos >>= 8;
+ bw->writeRun = -1;
+ }
+}
+
+// Decompress a block of text to intermediate buffer
+int read_bunzip_data(struct bunzip_data *bd)
+{
+ int rc = read_block_header(bd, bd->bwdata);
+ if (!rc) rc=read_huffman_data(bd, bd->bwdata);
+
+ // First thing that can be done by a background thread.
+ burrows_wheeler_prep(bd, bd->bwdata);
+
+ return rc;
+}
+
+// Undo burrows-wheeler transform on intermediate buffer to produce output.
+// If !len, write up to len bytes of data to buf. Otherwise write to out_fd.
+// Returns len ? bytes written : 0. Notice all errors are negative #'s.
+//
+// Burrows-wheeler transform is described at:
+// http://dogma.net/markn/articles/bwt/bwt.htm
+// http://marknelson.us/1996/09/01/bwt/
+
+int write_bunzip_data(struct bunzip_data *bd, struct bwdata *bw, int out_fd, char *outbuf, int len)
+{
+ unsigned int *dbuf = bw->dbuf;
+ int count, pos, current, run, copies, outbyte, previous, gotcount = 0;
+
+ for (;;) {
+ // If last read was short due to end of file, return last block now
+ if (bw->writeCount < 0) return bw->writeCount;
+
+ // If we need to refill dbuf, do it.
+ if (!bw->writeCount) {
+ int i = read_bunzip_data(bd);
+ if (i) {
+ if (i == RETVAL_LAST_BLOCK) {
+ bw->writeCount = i;
+ return gotcount;
+ } else return i;
+ }
+ }
+
+ // loop generating output
+ count = bw->writeCount;
+ pos = bw->writePos;
+ current = bw->writeCurrent;
+ run = bw->writeRun;
+ while (count) {
+
+ // If somebody (like tar) wants a certain number of bytes of
+ // data from memory instead of written to a file, humor them.
+ if (len && bd->outbufPos >= len) goto dataus_interruptus;
+ count--;
+
+ // Follow sequence vector to undo Burrows-Wheeler transform.
+ previous = current;
+ pos = dbuf[pos];
+ current = pos&0xff;
+ pos >>= 8;
+
+ // Whenever we see 3 consecutive copies of the same byte,
+ // the 4th is a repeat count
+ if (run++ == 3) {
+ copies = current;
+ outbyte = previous;
+ current = -1;
+ } else {
+ copies = 1;
+ outbyte = current;
+ }
+
+ // Output bytes to buffer, flushing to file if necessary
+ while (copies--) {
+ if (bd->outbufPos == IOBUF_SIZE) flush_bunzip_outbuf(bd, out_fd);
+ bd->outbuf[bd->outbufPos++] = outbyte;
+ bw->dataCRC = (bw->dataCRC << 8)
+ ^ bd->crc32Table[(bw->dataCRC >> 24) ^ outbyte];
+ }
+ if (current != previous) run=0;
+ }
+
+ // decompression of this block completed successfully
+ bw->dataCRC = ~(bw->dataCRC);
+ bd->totalCRC = ((bd->totalCRC << 1) | (bd->totalCRC >> 31)) ^ bw->dataCRC;
+
+ // if this block had a crc error, force file level crc error.
+ if (bw->dataCRC != bw->headerCRC) {
+ bd->totalCRC = bw->headerCRC+1;
+
+ return RETVAL_LAST_BLOCK;
+ }
+dataus_interruptus:
+ bw->writeCount = count;
+ if (len) {
+ gotcount += bd->outbufPos;
+ memcpy(outbuf, bd->outbuf, len);
+
+ // If we got enough data, checkpoint loop state and return
+ if ((len -= bd->outbufPos)<1) {
+ bd->outbufPos -= len;
+ if (bd->outbufPos) memmove(bd->outbuf, bd->outbuf+len, bd->outbufPos);
+ bw->writePos = pos;
+ bw->writeCurrent = current;
+ bw->writeRun = run;
+
+ return gotcount;
+ }
+ }
+ }
+}
+
+// Allocate the structure, read file header. If !len, src_fd contains
+// filehandle to read from. Else inbuf contains data.
+int start_bunzip(struct bunzip_data **bdp, int src_fd, char *inbuf, int len)
+{
+ struct bunzip_data *bd;
+ unsigned int i;
+
+ // Figure out how much data to allocate.
+ i = sizeof(struct bunzip_data);
+ if (!len) i += IOBUF_SIZE;
+
+ // Allocate bunzip_data. Most fields initialize to zero.
+ bd = *bdp = xzalloc(i);
+ if (len) {
+ bd->inbuf = inbuf;
+ bd->inbufCount = len;
+ bd->in_fd = -1;
+ } else {
+ bd->inbuf = (char *)(bd+1);
+ bd->in_fd = src_fd;
+ }
+
+ crc_init(bd->crc32Table, 0);
+
+ // Ensure that file starts with "BZh".
+ for (i=0;i<3;i++) if (get_bits(bd,8)!="BZh"[i]) return RETVAL_NOT_BZIP_DATA;
+
+ // Next byte ascii '1'-'9', indicates block size in units of 100k of
+ // uncompressed data. Allocate intermediate buffer for block.
+ i = get_bits(bd, 8);
+ if (i<'1' || i>'9') return RETVAL_NOT_BZIP_DATA;
+ bd->dbufSize = 100000*(i-'0')*THREADS;
+ for (i=0; i<THREADS; i++)
+ bd->bwdata[i].dbuf = xmalloc(bd->dbufSize * sizeof(int));
+
+ return 0;
+}
+
+// Example usage: decompress src_fd to dst_fd. (Stops at end of bzip data,
+// not end of file.)
+void bunzipStream(int src_fd, int dst_fd)
+{
+ struct bunzip_data *bd;
+ char *bunzip_errors[]={NULL, "not bzip", "bad data", "old format"};
+ int i, j;
+
+ if (!(i = start_bunzip(&bd,src_fd, 0, 0))) {
+ i = write_bunzip_data(bd,bd->bwdata, dst_fd, 0, 0);
+ if (i==RETVAL_LAST_BLOCK && bd->bwdata[0].headerCRC==bd->totalCRC) i = 0;
+ }
+ flush_bunzip_outbuf(bd, dst_fd);
+
+ for (j=0; j<THREADS; j++) free(bd->bwdata[j].dbuf);
+ free(bd);
+ if (i) error_exit(bunzip_errors[-i]);
+}
+
static void do_bzcat(int fd, char *name)
{
bunzipStream(fd, 1);