Another bzip2 update and speedup from Manuel Novoa III, with some

additional changes (primarily lots of comments) from Rob Landley.

1 files changed, 267 insertions, 223 deletions

diff --git a/archival/libunarchive/decompress_bunzip2.c b/archival/libunarchive/decompress_bunzip2.c
index b4bcb0b49..f00c43913 100644
--- a/archival/libunarchive/decompress_bunzip2.c
+++ b/archival/libunarchive/decompress_bunzip2.c
@@ -10,6 +10,36 @@
                 LGPL (http://www.gnu.org/copyleft/lgpl.html
 */
 
+/*
+        Size and speed optimizations by Manuel Novoa III  (mjn3@codepoet.org).
+
+        More efficient reading of huffman codes, a streamlined read_bunzip()
+        function, and various other tweaks.  In (limited) tests, approximately
+        20% faster than bzcat on x86 and about 10% faster on arm.
+
+        Note that about 2/3 of the time is spent in read_unzip() reversing
+        the Burrows-Wheeler transformation.  Much of that time is delay
+        resulting from cache misses.
+
+        I would ask that anyone benefiting from this work, especially those
+        using it in commercial products, consider making a donation to my local
+        non-profit hospice organization in the name of the woman I loved, who
+        passed away Feb. 12, 2003.
+
+                In memory of Toni W. Hagan
+
+                Hospice of Acadiana, Inc.
+                2600 Johnston St., Suite 200
+                Lafayette, LA 70503-3240
+
+                Phone (337) 232-1234 or 1-800-738-2226
+                Fax   (337) 232-1297
+
+                http://www.hospiceacadiana.com/
+
+        Manuel
+ */
+
 #include <setjmp.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -38,39 +68,31 @@
 /* Other housekeeping constants */
 #define IOBUF_SIZE                      4096
 
-static char * const bunzip_errors[]={NULL,"Bad file checksum","Not bzip data",
-                "Unexpected input EOF","Unexpected output EOF","Data error",
-                 "Out of memory","Obsolete (pre 0.9.5) bzip format not supported."};
-
 /* This is what we know about each huffman coding group */
 struct group_data {
         /* We have an extra slot at the end of limit[] for a sentinal value. */
         int limit[MAX_HUFCODE_BITS+1],base[MAX_HUFCODE_BITS],permute[MAX_SYMBOLS];
-        char minLen, maxLen;
+        int minLen, maxLen;
 };
 
 /* Structure holding all the housekeeping data, including IO buffers and
    memory that persists between calls to bunzip */
 typedef struct {
-        /* For I/O error handling */
-        jmp_buf jmpbuf;
-        /* Input stream, input buffer, input bit buffer */
-        int in_fd,inbufCount,inbufPos;
-        unsigned char *inbuf;
+        /* State for interrupting output loop */
+        int writeCopies,writePos,writeRunCountdown,writeCount,writeCurrent;
+        /* I/O tracking data (file handles, buffers, positions, etc.) */
+        int in_fd,out_fd,inbufCount,inbufPos /*,outbufPos*/;
+        unsigned char *inbuf /*,*outbuf*/;
         unsigned int inbufBitCount, inbufBits;
-        /* Output buffer */
-        char outbuf[IOBUF_SIZE];
-        int outbufPos;
         /* The CRC values stored in the block header and calculated from the data */
-        unsigned int crc32Table[256],headerCRC, dataCRC, totalCRC;
+        unsigned int crc32Table[256],headerCRC, totalCRC, writeCRC;
         /* Intermediate buffer and its size (in bytes) */
         unsigned int *dbuf, dbufSize;
-        /* State for interrupting output loop */
-        int writePos,writeRun,writeCount,writeCurrent;
-
         /* These things are a bit too big to go on the stack */
         unsigned char selectors[32768];                 /* nSelectors=15 bits */
         struct group_data groups[MAX_GROUPS];   /* huffman coding tables */
+        /* For I/O error handling */
+        jmp_buf jmpbuf;
 } bunzip_data;
 
 /* Return the next nnn bits of input.  All reads from the compressed input
@@ -106,39 +128,29 @@ static unsigned int get_bits(bunzip_data *bd, char bits_wanted)
         return bits;
 }
 
-/* At certain times, it pays to have an optimized inline version of
- * get_bits() which gets a single bit. */
-#define GET_A_BIT(bd) \
-   ((bd->inbufBitCount > 0) \
-        ? ((unsigned int)(((bd)->inbufBits >> --(bd)->inbufBitCount) & 1)) \
-        : get_bits((bd), 1))
-
-
-/* Decompress a block of text to into intermediate buffer */
+/* Unpacks the next block and sets up for the inverse burrows-wheeler step. */
 
-extern int read_bunzip_data(bunzip_data *bd)
+static int get_next_block(bunzip_data *bd)
 {
         struct group_data *hufGroup;
-        int dbufCount,nextSym,dbufSize,origPtr,groupCount,*base,*limit,selector,
+        int dbufCount,nextSym,dbufSize,groupCount,*base,*limit,selector,
                 i,j,k,t,runPos,symCount,symTotal,nSelectors,byteCount[256];
         unsigned char uc, symToByte[256], mtfSymbol[256], *selectors;
-        unsigned int *dbuf;
-
-        /* Read in header signature (borrowing mtfSymbol for temp space). */
-        for(i=0;i<6;i++) mtfSymbol[i]=get_bits(bd,8);
-        mtfSymbol[6]=0;
-        /* Read CRC (which is stored big endian). */
-        bd->headerCRC=get_bits(bd,32);
-        /* Is this the last block (with CRC for file)? */
-        if(!strcmp(mtfSymbol,"\x17\x72\x45\x38\x50\x90"))
-                return RETVAL_LAST_BLOCK;
-        /* If it's not a valid data block, barf. */
-        if(strcmp(mtfSymbol,"\x31\x41\x59\x26\x53\x59"))
-                return RETVAL_NOT_BZIP_DATA;
+        unsigned int *dbuf,origPtr;
 
         dbuf=bd->dbuf;
         dbufSize=bd->dbufSize;
         selectors=bd->selectors;
+        /* Reset longjmp I/O error handling */
+        i=setjmp(bd->jmpbuf);
+        if(i) return i;
+        /* Read in header signature and CRC, then validate signature.
+           (last block signature means CRC is for whole file, return now) */
+        i = get_bits(bd,24);
+        j = get_bits(bd,24);
+        bd->headerCRC=get_bits(bd,32);
+        if ((i == 0x177245) && (j == 0x385090)) return RETVAL_LAST_BLOCK;
+        if ((i != 0x314159) || (j != 0x265359)) return RETVAL_NOT_BZIP_DATA;
         /* We can add support for blockRandomised if anybody complains.  There was
            some code for this in busybox 1.0.0-pre3, but nobody ever noticed that
            it didn't actually work. */
@@ -150,10 +162,6 @@ extern int read_bunzip_data(bunzip_data *bd)
            values were present.  We make a translation table to convert the symbols
            back to the corresponding bytes. */
         t=get_bits(bd, 16);
-#if 0
-        /* I don't believe this is necessary.  Rob? */
-        memset(symToByte,0,256);
-#endif
         symTotal=0;
         for (i=0;i<16;i++) {
                 if(t&(1<<(15-i))) {
@@ -167,7 +175,8 @@ extern int read_bunzip_data(bunzip_data *bd)
         if (groupCount<2 || groupCount>MAX_GROUPS) return RETVAL_DATA_ERROR;
         /* nSelectors: Every GROUP_SIZE many symbols we select a new huffman coding
            group.  Read in the group selector list, which is stored as MTF encoded
-           bit runs. */
+           bit runs.  (MTF=Move To Front, as each value is used it's moved to the
+           start of the list.) */
         if(!(nSelectors=get_bits(bd, 15))) return RETVAL_DATA_ERROR;
         for(i=0; i<groupCount; i++) mtfSymbol[i] = i;
         for(i=0; i<nSelectors; i++) {
@@ -175,13 +184,7 @@ extern int read_bunzip_data(bunzip_data *bd)
                 for(j=0;get_bits(bd,1);j++) if (j>=groupCount) return RETVAL_DATA_ERROR;
                 /* Decode MTF to get the next selector */
                 uc = mtfSymbol[j];
-                /* A very small amount of data to move, so memmove is overkill
-                 * and bigger at least in my tests. */
-                k = j;
-                while (k) {
-                        mtfSymbol[k] = mtfSymbol[k-1];
-                        --k;
-                }
+                for(;j;j--) mtfSymbol[j] = mtfSymbol[j-1];
                 mtfSymbol[0]=selectors[i]=uc;
         }
         /* Read the huffman coding tables for each group, which code for symTotal
@@ -190,16 +193,30 @@ extern int read_bunzip_data(bunzip_data *bd)
         for (j=0; j<groupCount; j++) {
                 unsigned char length[MAX_SYMBOLS],temp[MAX_HUFCODE_BITS+1];
                 int     minLen, maxLen, pp;
-                /* Read lengths */
-                t=get_bits(bd, 5) - 1;  /* This lets us avoid a test in the loop. */
+                /* Read huffman code lengths for each symbol.  They're stored in
+                   a way similar to mtf; record a starting value for the first symbol,
+                   and an offset from the previous value for everys symbol after that.
+                   (Subtracting 1 before the loop and then adding it back at the end is
+                   an optimization that makes the test inside the loop simpler: symbol
+                   length 0 becomes negative, so an unsigned inequality catches it.) */
+                t=get_bits(bd, 5)-1;
                 for (i = 0; i < symCount; i++) {
                         for(;;) {
-                                if (((unsigned)t) > (MAX_HUFCODE_BITS-1)) return RETVAL_DATA_ERROR;
-                                        if(!get_bits(bd, 1)) break;
-                                        /* We can avoid an if/else with a little arithmetic. */
-                                        t += (1 - 2*get_bits(bd, 1)); /* 0 -> t++ ; 1 -> t-- */
+                                if (((unsigned)t) > (MAX_HUFCODE_BITS-1))
+                                        return RETVAL_DATA_ERROR;
+                                /* If first bit is 0, stop.  Else second bit indicates whether
+                                   to increment or decrement the value.  Optimization: grab 2
+                                   bits and unget the second if the first was 0. */
+                                k = get_bits(bd,2);
+                                if (k < 2) {
+                                        bd->inbufBitCount++;
+                                        break;
+                                }
+                                /* Add one if second bit 1, else subtract 1.  Avoids if/else */
+                                t+=(((k+1)&2)-1);
                         }
-                        length[i] = t + 1;      /* Correct for the initial -1 adjustment. */
+                        /* Correct for the initial -1, to get the final symbol length */
+                        length[i]=t+1;
                 }
                 /* Find largest and smallest lengths in this group */
                 minLen=maxLen=length[0];
@@ -214,11 +231,8 @@ extern int read_bunzip_data(bunzip_data *bd)
                  * 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]].
+                 * number of bits can have.  This is how the huffman codes can vary in
+                 * length: each code with a value>limit[length] needs another bit.
                  */
                 hufGroup=bd->groups+j;
                 hufGroup->minLen = minLen;
@@ -228,22 +242,29 @@ extern int read_bunzip_data(bunzip_data *bd)
                    entry.  We do this again when using them (during symbol decoding).*/
                 base=hufGroup->base-1;
                 limit=hufGroup->limit-1;
-                /* Calculate permute[] */
-                pp = 0;
-                for(i=minLen;i<=maxLen;i++) 
+                /* Calculate permute[].  Concurently, initialize temp[] and limit[]. */
+                pp=0;
+                for(i=minLen;i<=maxLen;i++) {
+                        temp[i]=limit[i]=0;
                         for(t=0;t<symCount;t++) 
                                 if(length[t]==i) hufGroup->permute[pp++] = t;
-                /* Count cumulative symbols coded for at each bit length */
-                for (i=minLen;i<=maxLen;i++) temp[i]=limit[i]=0;
+                }
+                /* Count symbols coded for at each bit length */
                 for (i=0;i<symCount;i++) temp[length[i]]++;
                 /* 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-cumulative count of symbols coded for already). */
+                 * limit minus the cumulative count of symbols coded for already). */
                 pp=t=0;
                 for (i=minLen; i<maxLen; i++) {
                         pp+=temp[i];
-                        limit[i]=pp-1;
+                        /* We read the largest possible symbol size and then unget bits
+                           after determining how many we need, and those extra bits could
+                           be set to anything.  (They're noise from future symbols.)  At
+                           each level we're really only interested in the first few bits,
+                           so here we set all the trailing to-be-ignored bits to 1 so they
+                           don't affect the value>limit[length] comparison. */
+                        limit[i]= (pp << (maxLen - i)) - 1;
                         pp<<=1;
                         base[i+1]=pp-(t+=temp[i]);
                 }
@@ -255,10 +276,12 @@ extern int read_bunzip_data(bunzip_data *bd)
            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 */
-        memset(byteCount,0,256*sizeof(int));
-        for(i=0;i<256;i++) mtfSymbol[i]=(unsigned char)i;
-        /* Loop through compressed symbols */
+        /* Initialize symbol occurrence counters and symbol Move To Front table */
+        for(i=0;i<256;i++) {
+                byteCount[i] = 0;
+                mtfSymbol[i]=(unsigned char)i;
+        }
+        /* Loop through compressed symbols. */
         runPos=dbufCount=symCount=selector=0;
         for(;;) {
                 /* Determine which huffman coding group to use. */
@@ -269,17 +292,41 @@ extern int read_bunzip_data(bunzip_data *bd)
                         base=hufGroup->base-1;
                         limit=hufGroup->limit-1;
                 }
-                /* Read next huffman-coded symbol */
-                i = hufGroup->minLen;
-                j=get_bits(bd, i);
-                while (j > limit[i]) { /* The sentinal allows us to avoid testing i. */
-                        j = (j << 1) | GET_A_BIT(bd);
-                        ++i;
-                }
-                /* Huffman decode nextSym (with bounds checking) */
-                if ((i > hufGroup->maxLen) || (((unsigned)(j-=base[i])) >= MAX_SYMBOLS)) return RETVAL_DATA_ERROR;
+                /* Read next huffman-coded symbol. */
+                /* Note: It is far cheaper to read maxLen bits and back up than it is
+                   to read minLen bits and then an additional bit at a time, testing
+                   as we go.  Because there is a trailing last block (with file CRC),
+                   there is no danger of the overread causing an unexpected EOF for a
+                   valid compressed file.  As a further optimization, we do the read
+                   inline (falling back to a call to get_bits if the buffer runs
+                   dry).  The following (up to got_huff_bits:) is equivalent to
+                   j=get_bits(bd,hufGroup->maxLen);
+                 */
+                while (bd->inbufBitCount<hufGroup->maxLen) {
+                        if(bd->inbufPos==bd->inbufCount) {
+                                j = get_bits(bd,hufGroup->maxLen);
+                                goto got_huff_bits;
+                        }
+                        bd->inbufBits=(bd->inbufBits<<8)|bd->inbuf[bd->inbufPos++];
+                        bd->inbufBitCount+=8;
+                };
+                bd->inbufBitCount-=hufGroup->maxLen;
+                j = (bd->inbufBits>>bd->inbufBitCount)&((1<<hufGroup->maxLen)-1);
+got_huff_bits:
+                /* Figure how how many bits are in next symbol and unget extras */
+                i=hufGroup->minLen;
+                while(j>limit[i]) ++i;
+                bd->inbufBitCount += (hufGroup->maxLen - i);
+                /* Huffman decode value to get nextSym (with bounds checking) */
+                if ((i > hufGroup->maxLen)
+                        || (((unsigned)(j=(j>>(hufGroup->maxLen-i))-base[i]))
+                                >= MAX_SYMBOLS))
+                        return RETVAL_DATA_ERROR;
                 nextSym = hufGroup->permute[j];
-                /* If this is a repeated run, loop collecting data */
+                /* We have now decoded the symbol, which indicates either a new literal
+                   byte, or a repeated run of the most recent literal byte.  First,
+                   check if nextSym indicates a repeated run, and if so loop collecting
+                   how many times to repeat the last literal. */
                 if (((unsigned)nextSym) <= SYMBOL_RUNB) { /* RUNA or RUNB */
                         /* If this is the start of a new run, zero out counter */
                         if(!runPos) {
@@ -311,19 +358,20 @@ extern int read_bunzip_data(bunzip_data *bd)
                 }
                 /* Is this the terminating symbol? */
                 if(nextSym>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.) */
+                /* At this point, nextSym 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.  But another instance of the
+                   first symbol in the mtf array, position 0, would have been handled
+                   as part of a run above.  Therefore 1 unused mtf position minus
+                   2 non-literal nextSym values equals -1.) */
                 if(dbufCount>=dbufSize) return RETVAL_DATA_ERROR;
                 i = nextSym - 1;
                 uc = mtfSymbol[i];
-                /* Since we typically expect to move only a small number of symbols,
-                 * and are bound by 256 in any case, using memmove here would
-                 * typically be slower due to function call overhead and other
-                 * assorted setup costs. */
+                /* Adjust the MTF array.  Since we typically expect to move only a
+                 * small number of symbols, and are bound by 256 in any case, using
+                 * memmove here would typically be bigger and slower due to function
+                 * call overhead and other assorted setup costs. */
                 do {
                         mtfSymbol[i] = mtfSymbol[i-1];
                 } while (--i);
@@ -333,14 +381,12 @@ extern int read_bunzip_data(bunzip_data *bd)
                 byteCount[uc]++;
                 dbuf[dbufCount++] = (unsigned int)uc;
         }
-        /* At this point, we've finished reading huffman-coded symbols and
-           compressed runs from the input stream.  There are dbufCount many of
-           them in dbuf[].  Now undo the Burrows-Wheeler transform on dbuf.
+        /* At this point, we've read all the huffman-coded symbols (and repeated
+       runs) for this block from the input stream, and decoded them into the
+           intermediate buffer.  There are dbufCount many decoded bytes in dbuf[].
+           Now undo the Burrows-Wheeler transform on dbuf.
            See http://dogma.net/markn/articles/bwt/bwt.htm
          */
-
-        /* Now we know what dbufCount is, do a better sanity check on origPtr.  */
-        if (((unsigned)origPtr)>=dbufCount) return RETVAL_DATA_ERROR;
         /* Turn byteCount into cumulative occurrence counts of 0 to n-1. */
         j=0;
         for(i=0;i<256;i++) {
@@ -350,144 +396,137 @@ extern int read_bunzip_data(bunzip_data *bd)
         }
         /* Figure out what order dbuf would be in if we sorted it. */
         for (i=0;i<dbufCount;i++) {
-                uc = (unsigned char)(dbuf[i] & 0xff);
+                uc=(unsigned char)(dbuf[i] & 0xff);
                 dbuf[byteCount[uc]] |= (i << 8);
                 byteCount[uc]++;
         }
-        /* blockRandomised support would go here. */
-
-        /* Using i as position, j as previous character, t as current character,
-           and uc as run count */
-        bd->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). */
+           it doesn't qualify as a run (hence writeRunCountdown=5). */
         if(dbufCount) {
+                if(origPtr>=dbufCount) return RETVAL_DATA_ERROR;
                 bd->writePos=dbuf[origPtr];
             bd->writeCurrent=(unsigned char)(bd->writePos&0xff);
                 bd->writePos>>=8;
-                bd->writeRun=-1;
+                bd->writeRunCountdown=5;
         }
         bd->writeCount=dbufCount;
 
         return RETVAL_OK;
 }
 
-/* Flush output buffer to disk */
-extern void flush_bunzip_outbuf(bunzip_data *bd, int out_fd)
-{
-        if(bd->outbufPos) {
-                if(write(out_fd, bd->outbuf, bd->outbufPos) != bd->outbufPos)
-                        longjmp(bd->jmpbuf,RETVAL_UNEXPECTED_OUTPUT_EOF);
-                bd->outbufPos=0;
-        }
-}
-
-
 /* 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 : RETVAL_OK.  Notice all errors negative #'s. */
-extern int write_bunzip_data(bunzip_data *bd, int out_fd, char *outbuf, int len)
+   If start_bunzip was initialized with out_fd=-1, then up to len bytes of
+   data are written to outbuf.  Return value is number of bytes written or
+   error (all errors are negative numbers).  If out_fd!=-1, outbuf and len
+   are ignored, data is written to out_fd and return is RETVAL_OK or error.
+*/
+
+extern int read_bunzip(bunzip_data *bd, char *outbuf, int len)
 {
-        unsigned int *dbuf=bd->dbuf;
-        int count,pos,current, run,copies,outbyte,previous,gotcount=0;
+        const unsigned int *dbuf;
+        int pos,current,previous,gotcount;
 
-        for(;;) {
-                /* If last read was short due to end of file, return last block now */
-                if(bd->writeCount<0) return bd->writeCount;
-                /* If we need to refill dbuf, do it. */
-                if(!bd->writeCount) {
-                        int i=read_bunzip_data(bd);
-                        if(i) {
-                                if(i==RETVAL_LAST_BLOCK) {
-                                        bd->writeCount=i;
-                                        return gotcount;
-                                } else return i;
+        /* If last read was short due to end of file, return last block now */
+        if(bd->writeCount<0) return bd->writeCount;
+
+        gotcount = 0;
+        dbuf=bd->dbuf;
+        pos=bd->writePos;
+        current=bd->writeCurrent;
+
+        /* We will always have pending decoded data to write into the output
+           buffer unless this is the very first call (in which case we haven't
+           huffman-decoded a block into the intermediate buffer yet). */
+
+        if (bd->writeCopies) {
+                /* Inside the loop, writeCopies means extra copies (beyond 1) */
+                --bd->writeCopies;
+                /* Loop outputting bytes */
+                for(;;) {
+                        /* If the output buffer is full, snapshot state and return */
+                        if(gotcount >= len) {
+                                bd->writePos=pos;
+                                bd->writeCurrent=current;
+                                bd->writeCopies++;
+                                return len;
                         }
-                }
-                /* Loop generating output */
-                count=bd->writeCount;
-                pos=bd->writePos;
-                current=bd->writeCurrent;
-                run=bd->writeRun;
-                while(count) {
-                        /* If somebody (like busybox 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--;
+                        /* Write next byte into output buffer, updating CRC */
+                        outbuf[gotcount++] = current;
+                        bd->writeCRC=(((bd->writeCRC)<<8)
+                                                  ^bd->crc32Table[((bd->writeCRC)>>24)^current]);
+                        /* Loop now if we're outputting multiple copies of this byte */
+                        if (bd->writeCopies) {
+                                --bd->writeCopies;
+                                continue;
+                        }
+decode_next_byte:
+                        if (!bd->writeCount--) break;
                         /* 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;
+                        /* After 3 consecutive copies of the same byte, the 4th is a repeat
+                           count.  We count down from 4 instead
+                         * of counting up because testing for non-zero is faster */
+                        if(--bd->writeRunCountdown) {
+                                if(current!=previous) bd->writeRunCountdown=4;
                         } 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;
-                                bd->dataCRC = (bd->dataCRC << 8)
-                                                                ^ bd->crc32Table[(bd->dataCRC >> 24) ^ outbyte];
+                                /* We have a repeated run, this byte indicates the count */
+                                bd->writeCopies=current;
+                                current=previous;
+                                bd->writeRunCountdown=5;
+                                /* Sometimes there are just 3 bytes (run length 0) */
+                                if(!bd->writeCopies) goto decode_next_byte;
+                                /* Subtract the 1 copy we'd output anyway to get extras */
+                                --bd->writeCopies;
                         }
-                        if(current!=previous) run=0;
                 }
                 /* Decompression of this block completed successfully */
-                bd->dataCRC=~(bd->dataCRC);
-                bd->totalCRC=((bd->totalCRC << 1) | (bd->totalCRC >> 31)) ^ bd->dataCRC;
+                bd->writeCRC=~bd->writeCRC;
+                bd->totalCRC=((bd->totalCRC<<1) | (bd->totalCRC>>31)) ^ bd->writeCRC;
                 /* If this block had a CRC error, force file level CRC error. */
-                if(bd->dataCRC!=bd->headerCRC) {
+                if(bd->writeCRC!=bd->headerCRC) {
                         bd->totalCRC=bd->headerCRC+1;
                         return RETVAL_LAST_BLOCK;
                 }
-dataus_interruptus:
-                bd->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);
-                                bd->writePos=pos;
-                                bd->writeCurrent=current;
-                                bd->writeRun=run;
-                                return gotcount;
-                        }
-                }
         }
+
+        /* Refill the intermediate buffer by huffman-decoding next block of input */
+        /* (previous is just a convenient unused temp variable here) */
+        previous=get_next_block(bd);
+        if(previous) {
+                bd->writeCount=previous;
+                return (previous!=RETVAL_LAST_BLOCK) ? previous : gotcount;
+        }
+        bd->writeCRC=0xffffffffUL;
+        pos=bd->writePos;
+        current=bd->writeCurrent;
+        goto decode_next_byte;
 }
 
-/* Allocate the structure, read file header.  If !len, src_fd contains
-   filehandle to read from.  Else inbuf contains data. */
-extern int start_bunzip(bunzip_data **bdp, int src_fd, char *inbuf, int len)
+/* Allocate the structure, read file header.  If in_fd==-1, inbuf must contain
+   a complete bunzip file (len bytes long).  If in_fd!=-1, inbuf and len are
+   ignored, and data is read from file handle into temporary buffer. */
+extern int start_bunzip(bunzip_data **bdp, int in_fd, char *inbuf, int len)
 {
         bunzip_data *bd;
         unsigned int i,j,c;
+        const unsigned int BZh0=(((unsigned int)'B')<<24)+(((unsigned int)'Z')<<16)
+                                                        +(((unsigned int)'h')<<8)+(unsigned int)'0';
 
         /* Figure out how much data to allocate */
         i=sizeof(bunzip_data);
-        if(!len) i+=IOBUF_SIZE;
+        if(in_fd!=-1) i+=IOBUF_SIZE;
         /* Allocate bunzip_data.  Most fields initialize to zero. */
         if(!(bd=*bdp=malloc(i))) return RETVAL_OUT_OF_MEMORY;
         memset(bd,0,sizeof(bunzip_data));
-        if(len) {
+        /* Setup input buffer */
+        if(-1==(bd->in_fd=in_fd)) {
                 bd->inbuf=inbuf;
                 bd->inbufCount=len;
-                bd->in_fd=-1;
-        } else {
-                bd->inbuf=(char *)(bd+1);
-                bd->in_fd=src_fd;
-        }
+        } else bd->inbuf=(unsigned char *)(bd+1);
         /* Init the CRC32 table (big endian) */
         for(i=0;i<256;i++) {
                 c=i<<24;
@@ -498,55 +537,60 @@ extern int start_bunzip(bunzip_data **bdp, int src_fd, char *inbuf, int len)
         /* Setup for I/O error handling via longjmp */
         i=setjmp(bd->jmpbuf);
         if(i) return i;
-        /* 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
+
+        /* Ensure that file starts with "BZh['1'-'9']." */
+        i = get_bits(bd,32);
+        if (((unsigned int)(i-BZh0-1)) >= 9) return RETVAL_NOT_BZIP_DATA;
+
+        /* Fourth 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');
+        bd->dbufSize=100000*(i-BZh0);
+
         if(!(bd->dbuf=malloc(bd->dbufSize * sizeof(int))))
                 return RETVAL_OUT_OF_MEMORY;
         return RETVAL_OK;
 }
 
-extern char *uncompressStream(int src_fd, int dst_fd)
+/* Example usage: decompress src_fd to dst_fd.  (Stops at end of bzip data,
+   not end of file.) */
+extern int uncompressStream(int src_fd, int dst_fd)
 {
+        char *outbuf;
         bunzip_data *bd;
         int i;
 
+        if(!(outbuf=malloc(IOBUF_SIZE))) return RETVAL_OUT_OF_MEMORY;
         if(!(i=start_bunzip(&bd,src_fd,0,0))) {
-                i=write_bunzip_data(bd,dst_fd,0,0);
-                if(i==RETVAL_LAST_BLOCK && bd->headerCRC==bd->totalCRC) i=RETVAL_OK;
+                for(;;) {
+                        if((i=read_bunzip(bd,outbuf,IOBUF_SIZE)) <= 0) break;
+                        if(i!=write(dst_fd,outbuf,i)) {
+                                i=RETVAL_UNEXPECTED_OUTPUT_EOF;
+                                break;
+                        }
+                }
         }
-        flush_bunzip_outbuf(bd,dst_fd);
+        /* Check CRC and release memory */
+        if(i==RETVAL_LAST_BLOCK && bd->headerCRC==bd->totalCRC) i=RETVAL_OK;
         if(bd->dbuf) free(bd->dbuf);
         free(bd);
-        return bunzip_errors[-i];
+        free(outbuf);
+        return i;
 }
 
-/* This new version is not yet properly integrated with tar */
-extern ssize_t read_bz2(int fd, void *buf, size_t count)
-{
-#warning FIXME
-        return(0);
-}
+#ifdef TESTING
 
-extern void BZ2_bzReadOpen(int fd, void *unused, int nUnused)
-{
-#warning FIXME
-        return;
-}
-extern void BZ2_bzReadClose(void)
-{
-#warning FIXME
-}
+static char * const bunzip_errors[]={NULL,"Bad file checksum","Not bzip data",
+                "Unexpected input EOF","Unexpected output EOF","Data error",
+                 "Out of memory","Obsolete (pre 0.9.5) bzip format not supported."};
 
-#if 0
 /* Dumb little test thing, decompress stdin to stdout */
 int main(int argc, char *argv[])
 {
-        char *c=uncompressStream(0,1);
-        fprintf(stderr,"\n%s\n", c ? c : "Completed OK");
+        int i=uncompressStream(0,1);
+        char c;
+
+        if(i) fprintf(stderr,"%s\n", bunzip_errors[-i]);
+    else if(read(0,&c,1)) fprintf(stderr,"Trailing garbage ignored\n");
+        return -i;
 }
 #endif