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Member "rufus-3.13/src/bled/decompress_bunzip2.c" (20 Nov 2020, 27547 Bytes) of package /linux/misc/rufus-3.13.tar.gz:


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    1 /* vi: set sw=4 ts=4: */
    2 /* Small bzip2 deflate implementation, by Rob Landley (rob@landley.net).
    3 
    4    Based on bzip2 decompression code by Julian R Seward (jseward@acm.org),
    5    which also acknowledges contributions by Mike Burrows, David Wheeler,
    6    Peter Fenwick, Alistair Moffat, Radford Neal, Ian H. Witten,
    7    Robert Sedgewick, and Jon L. Bentley.
    8 
    9    Licensed under GPLv2 or later, see file LICENSE in this source tree.
   10 */
   11 
   12 /*
   13     Size and speed optimizations by Manuel Novoa III  (mjn3@codepoet.org).
   14 
   15     More efficient reading of Huffman codes, a streamlined read_bunzip()
   16     function, and various other tweaks.  In (limited) tests, approximately
   17     20% faster than bzcat on x86 and about 10% faster on arm.
   18 
   19     Note that about 2/3 of the time is spent in read_bunzip() reversing
   20     the Burrows-Wheeler transformation.  Much of that time is delay
   21     resulting from cache misses.
   22 
   23     (2010 update by vda: profiled "bzcat <84mbyte.bz2 >/dev/null"
   24     on x86-64 CPU with L2 > 1M: get_next_block is hotter than read_bunzip:
   25     %time seconds   calls function
   26     71.01   12.69     444 get_next_block
   27     28.65    5.12   93065 read_bunzip
   28     00.22    0.04 7736490 get_bits
   29     00.11    0.02      47 dealloc_bunzip
   30     00.00    0.00   93018 full_write
   31     ...)
   32 
   33 
   34     I would ask that anyone benefiting from this work, especially those
   35     using it in commercial products, consider making a donation to my local
   36     non-profit hospice organization (www.hospiceacadiana.com) in the name of
   37     the woman I loved, Toni W. Hagan, who passed away Feb. 12, 2003.
   38 
   39     Manuel
   40  */
   41 
   42 #include "libbb.h"
   43 #include "bb_archive.h"
   44 
   45 #if 0
   46 # define dbg(...) bb_error_msg(__VA_ARGS__)
   47 #else
   48 # define dbg(...) ((void)0)
   49 #endif
   50 
   51 /* Constants for Huffman coding */
   52 #define MAX_GROUPS          6
   53 #define GROUP_SIZE          50      /* 64 would have been more efficient */
   54 #define MAX_HUFCODE_BITS    20      /* Longest Huffman code allowed */
   55 #define MAX_SYMBOLS         258     /* 256 literals + RUNA + RUNB */
   56 #define SYMBOL_RUNA         0
   57 #define SYMBOL_RUNB         1
   58 
   59 /* Status return values */
   60 #define RETVAL_OK                       0
   61 #define RETVAL_LAST_BLOCK               (dbg("%d", __LINE__), -1)
   62 #define RETVAL_NOT_BZIP_DATA            (dbg("%d", __LINE__), -2)
   63 #define RETVAL_UNEXPECTED_INPUT_EOF     (dbg("%d", __LINE__), -3)
   64 #define RETVAL_SHORT_WRITE              (dbg("%d", __LINE__), -4)
   65 #define RETVAL_DATA_ERROR               (dbg("%d", __LINE__), -5)
   66 #define RETVAL_OUT_OF_MEMORY            (dbg("%d", __LINE__), -6)
   67 #define RETVAL_OBSOLETE_INPUT           (dbg("%d", __LINE__), -7)
   68 
   69 /* Other housekeeping constants */
   70 #define IOBUF_SIZE          BB_BUFSIZE
   71 
   72 /* This is what we know about each Huffman coding group */
   73 struct group_data {
   74     /* We have an extra slot at the end of limit[] for a sentinel value. */
   75     int limit[MAX_HUFCODE_BITS+1], base[MAX_HUFCODE_BITS], permute[MAX_SYMBOLS];
   76     int minLen, maxLen;
   77 };
   78 
   79 /* Structure holding all the housekeeping data, including IO buffers and
   80  * memory that persists between calls to bunzip
   81  * Found the most used member:
   82  *  cat this_file.c | sed -e 's/"/ /g' -e "s/'/ /g" | xargs -n1 \
   83  *  | grep 'bd->' | sed 's/^.*bd->/bd->/' | sort | $PAGER
   84  * and moved it (inbufBitCount) to offset 0.
   85  */
   86 struct bunzip_data {
   87     /* I/O tracking data (file handles, buffers, positions, etc.) */
   88     unsigned inbufBitCount, inbufBits;
   89     int in_fd, out_fd, inbufCount, inbufPos /*, outbufPos*/;
   90     uint8_t *inbuf /*,*outbuf*/;
   91 
   92     /* State for interrupting output loop */
   93     int writeCopies, writePos, writeRunCountdown, writeCount;
   94     int writeCurrent; /* actually a uint8_t */
   95 
   96     /* The CRC values stored in the block header and calculated from the data */
   97     uint32_t headerCRC, totalCRC, writeCRC;
   98 
   99     /* Intermediate buffer and its size (in bytes) */
  100     uint32_t *dbuf;
  101     unsigned dbufSize;
  102 
  103     /* For I/O error handling */
  104     jmp_buf jmpbuf;
  105 
  106     /* Big things go last (register-relative addressing can be larger for big offsets) */
  107     uint32_t crc32Table[256];
  108     uint8_t selectors[32768];  /* nSelectors=15 bits */
  109     struct group_data groups[MAX_GROUPS];  /* Huffman coding tables */
  110 };
  111 /* typedef struct bunzip_data bunzip_data; -- done in .h file */
  112 
  113 
  114 /* Return the next nnn bits of input.  All reads from the compressed input
  115    are done through this function.  All reads are big endian */
  116 static unsigned get_bits(bunzip_data *bd, int bits_wanted)
  117 {
  118     unsigned bits = 0;
  119     /* Cache bd->inbufBitCount in a CPU register (hopefully): */
  120     int bit_count = bd->inbufBitCount;
  121 
  122     /* If we need to get more data from the byte buffer, do so.  (Loop getting
  123        one byte at a time to enforce endianness and avoid unaligned access.) */
  124     while (bit_count < bits_wanted) {
  125 
  126         /* If we need to read more data from file into byte buffer, do so */
  127         if (bd->inbufPos == bd->inbufCount) {
  128             /* if "no input fd" case: in_fd == -1, read fails, we jump */
  129             bd->inbufCount = safe_read(bd->in_fd, bd->inbuf, IOBUF_SIZE);
  130             if (bd->inbufCount <= 0)
  131                 longjmp(bd->jmpbuf, RETVAL_UNEXPECTED_INPUT_EOF);
  132             bd->inbufPos = 0;
  133         }
  134 
  135         /* Avoid 32-bit overflow (dump bit buffer to top of output) */
  136         if (bit_count >= 24) {
  137             bits = bd->inbufBits & ((1 << bit_count) - 1);
  138             bits_wanted -= bit_count;
  139             bits <<= bits_wanted;
  140             bit_count = 0;
  141         }
  142 
  143         /* Grab next 8 bits of input from buffer. */
  144         bd->inbufBits = (bd->inbufBits << 8) | bd->inbuf[bd->inbufPos++];
  145         bit_count += 8;
  146     }
  147 
  148     /* Calculate result */
  149     bit_count -= bits_wanted;
  150     bd->inbufBitCount = bit_count;
  151     bits |= (bd->inbufBits >> bit_count) & ((1 << bits_wanted) - 1);
  152 
  153     return bits;
  154 }
  155 
  156 /* Unpacks the next block and sets up for the inverse Burrows-Wheeler step. */
  157 static int get_next_block(bunzip_data *bd)
  158 {
  159     struct group_data *hufGroup;
  160     int dbufCount, dbufSize, groupCount, *base, *limit, selector,
  161         i, j, t, runPos, symCount, symTotal, nSelectors, byteCount[256];
  162     int runCnt;
  163     uint8_t uc, symToByte[256], mtfSymbol[256], *selectors;
  164     uint32_t *dbuf;
  165     unsigned origPtr;
  166 
  167     dbuf = bd->dbuf;
  168     dbufSize = bd->dbufSize;
  169     selectors = bd->selectors;
  170 
  171 /* In bbox, we are ok with aborting through setjmp which is set up in start_bunzip */
  172 #if 0
  173     /* Reset longjmp I/O error handling */
  174     i = setjmp(bd->jmpbuf);
  175     if (i) return i;
  176 #endif
  177 
  178     /* Read in header signature and CRC, then validate signature.
  179        (last block signature means CRC is for whole file, return now) */
  180     i = get_bits(bd, 24);
  181     j = get_bits(bd, 24);
  182     bd->headerCRC = get_bits(bd, 32);
  183     if ((i == 0x177245) && (j == 0x385090)) return RETVAL_LAST_BLOCK;
  184     if ((i != 0x314159) || (j != 0x265359)) return RETVAL_NOT_BZIP_DATA;
  185 
  186     /* We can add support for blockRandomised if anybody complains.  There was
  187        some code for this in busybox 1.0.0-pre3, but nobody ever noticed that
  188        it didn't actually work. */
  189     if (get_bits(bd, 1)) return RETVAL_OBSOLETE_INPUT;
  190     origPtr = get_bits(bd, 24);
  191     if ((int)origPtr > dbufSize) return RETVAL_DATA_ERROR;
  192 
  193     /* mapping table: if some byte values are never used (encoding things
  194        like ascii text), the compression code removes the gaps to have fewer
  195        symbols to deal with, and writes a sparse bitfield indicating which
  196        values were present.  We make a translation table to convert the symbols
  197        back to the corresponding bytes. */
  198     symTotal = 0;
  199     i = 0;
  200     t = get_bits(bd, 16);
  201     do {
  202         if (t & (1 << 15)) {
  203             unsigned inner_map = get_bits(bd, 16);
  204             do {
  205                 if (inner_map & (1 << 15))
  206                     symToByte[symTotal++] = i;
  207                 inner_map <<= 1;
  208                 i++;
  209             } while (i & 15);
  210             i -= 16;
  211         }
  212         t <<= 1;
  213         i += 16;
  214     } while (i < 256);
  215 
  216     /* How many different Huffman coding groups does this block use? */
  217     groupCount = get_bits(bd, 3);
  218     if (groupCount < 2 || groupCount > MAX_GROUPS)
  219         return RETVAL_DATA_ERROR;
  220 
  221     /* nSelectors: Every GROUP_SIZE many symbols we select a new Huffman coding
  222        group.  Read in the group selector list, which is stored as MTF encoded
  223        bit runs.  (MTF=Move To Front, as each value is used it's moved to the
  224        start of the list.) */
  225     for (i = 0; i < groupCount; i++)
  226         mtfSymbol[i] = i;
  227     nSelectors = get_bits(bd, 15);
  228     if (!nSelectors)
  229         return RETVAL_DATA_ERROR;
  230     for (i = 0; i < nSelectors; i++) {
  231         uint8_t tmp_byte;
  232         /* Get next value */
  233         int n = 0;
  234         while (get_bits(bd, 1)) {
  235             if (n >= groupCount) return RETVAL_DATA_ERROR;
  236             n++;
  237         }
  238         /* Decode MTF to get the next selector */
  239         tmp_byte = mtfSymbol[n];
  240         while (--n >= 0)
  241             mtfSymbol[n + 1] = mtfSymbol[n];
  242         mtfSymbol[0] = selectors[i] = tmp_byte;
  243     }
  244 
  245     /* Read the Huffman coding tables for each group, which code for symTotal
  246        literal symbols, plus two run symbols (RUNA, RUNB) */
  247     symCount = symTotal + 2;
  248     for (j = 0; j < groupCount; j++) {
  249         uint8_t length[MAX_SYMBOLS];
  250         /* 8 bits is ALMOST enough for temp[], see below */
  251         unsigned temp[MAX_HUFCODE_BITS+1];
  252         int minLen, maxLen, pp, len_m1;
  253 
  254         /* Read Huffman code lengths for each symbol.  They're stored in
  255            a way similar to mtf; record a starting value for the first symbol,
  256            and an offset from the previous value for every symbol after that.
  257            (Subtracting 1 before the loop and then adding it back at the end is
  258            an optimization that makes the test inside the loop simpler: symbol
  259            length 0 becomes negative, so an unsigned inequality catches it.) */
  260         len_m1 = get_bits(bd, 5) - 1;
  261         for (i = 0; i < symCount; i++) {
  262             for (;;) {
  263                 int two_bits;
  264                 if ((unsigned)len_m1 > (MAX_HUFCODE_BITS-1))
  265                     return RETVAL_DATA_ERROR;
  266 
  267                 /* If first bit is 0, stop.  Else second bit indicates whether
  268                    to increment or decrement the value.  Optimization: grab 2
  269                    bits and unget the second if the first was 0. */
  270                 two_bits = get_bits(bd, 2);
  271                 if (two_bits < 2) {
  272                     bd->inbufBitCount++;
  273                     break;
  274                 }
  275 
  276                 /* Add one if second bit 1, else subtract 1.  Avoids if/else */
  277                 len_m1 += (((two_bits+1) & 2) - 1);
  278             }
  279 
  280             /* Correct for the initial -1, to get the final symbol length */
  281             length[i] = len_m1 + 1;
  282         }
  283 
  284         /* Find largest and smallest lengths in this group */
  285         minLen = maxLen = length[0];
  286         for (i = 1; i < symCount; i++) {
  287             if (length[i] > maxLen) maxLen = length[i];
  288             else if (length[i] < minLen) minLen = length[i];
  289         }
  290 
  291         /* Calculate permute[], base[], and limit[] tables from length[].
  292          *
  293          * permute[] is the lookup table for converting Huffman coded symbols
  294          * into decoded symbols.  base[] is the amount to subtract from the
  295          * value of a Huffman symbol of a given length when using permute[].
  296          *
  297          * limit[] indicates the largest numerical value a symbol with a given
  298          * number of bits can have.  This is how the Huffman codes can vary in
  299          * length: each code with a value>limit[length] needs another bit.
  300          */
  301         hufGroup = bd->groups + j;
  302         hufGroup->minLen = minLen;
  303         hufGroup->maxLen = maxLen;
  304 
  305         /* Note that minLen can't be smaller than 1, so we adjust the base
  306            and limit array pointers so we're not always wasting the first
  307            entry.  We do this again when using them (during symbol decoding). */
  308         base = hufGroup->base - 1;
  309         limit = hufGroup->limit - 1;
  310 
  311         /* Calculate permute[].  Concurently, initialize temp[] and limit[]. */
  312         pp = 0;
  313         for (i = minLen; i <= maxLen; i++) {
  314             int k;
  315             temp[i] = limit[i] = 0;
  316             for (k = 0; k < symCount; k++)
  317                 if (length[k] == i)
  318                     hufGroup->permute[pp++] = k;
  319         }
  320 
  321         /* Count symbols coded for at each bit length */
  322         /* NB: in pathological cases, temp[8] can end ip being 256.
  323          * That's why uint8_t is too small for temp[]. */
  324         for (i = 0; i < symCount; i++) temp[length[i]]++;
  325 
  326         /* Calculate limit[] (the largest symbol-coding value at each bit
  327          * length, which is (previous limit<<1)+symbols at this level), and
  328          * base[] (number of symbols to ignore at each bit length, which is
  329          * limit minus the cumulative count of symbols coded for already). */
  330         pp = t = 0;
  331         for (i = minLen; i < maxLen;) {
  332             unsigned temp_i = temp[i];
  333 
  334             pp += temp_i;
  335 
  336             /* We read the largest possible symbol size and then unget bits
  337                after determining how many we need, and those extra bits could
  338                be set to anything.  (They're noise from future symbols.)  At
  339                each level we're really only interested in the first few bits,
  340                so here we set all the trailing to-be-ignored bits to 1 so they
  341                don't affect the value>limit[length] comparison. */
  342             limit[i] = (pp << (maxLen - i)) - 1;
  343             pp <<= 1;
  344             t += temp_i;
  345             base[++i] = pp - t;
  346         }
  347         limit[maxLen] = pp + temp[maxLen] - 1;
  348         limit[maxLen+1] = INT_MAX; /* Sentinel value for reading next sym. */
  349         base[minLen] = 0;
  350     }
  351 
  352     /* We've finished reading and digesting the block header.  Now read this
  353        block's Huffman coded symbols from the file and undo the Huffman coding
  354        and run length encoding, saving the result into dbuf[dbufCount++] = uc */
  355 
  356     /* Initialize symbol occurrence counters and symbol Move To Front table */
  357     /*memset(byteCount, 0, sizeof(byteCount)); - smaller, but slower */
  358     for (i = 0; i < 256; i++) {
  359         byteCount[i] = 0;
  360         mtfSymbol[i] = (uint8_t)i;
  361     }
  362 
  363     /* Loop through compressed symbols. */
  364 
  365     runPos = dbufCount = selector = 0;
  366     for (;;) {
  367         int nextSym;
  368 
  369         /* Fetch next Huffman coding group from list. */
  370         symCount = GROUP_SIZE - 1;
  371         if (selector >= nSelectors) return RETVAL_DATA_ERROR;
  372         hufGroup = bd->groups + selectors[selector++];
  373         base = hufGroup->base - 1;
  374         limit = hufGroup->limit - 1;
  375 
  376  continue_this_group:
  377         /* Read next Huffman-coded symbol. */
  378 
  379         /* Note: It is far cheaper to read maxLen bits and back up than it is
  380            to read minLen bits and then add additional bit at a time, testing
  381            as we go.  Because there is a trailing last block (with file CRC),
  382            there is no danger of the overread causing an unexpected EOF for a
  383            valid compressed file.
  384          */
  385         if (1) {
  386             /* As a further optimization, we do the read inline
  387                (falling back to a call to get_bits if the buffer runs dry).
  388              */
  389             int new_cnt;
  390             while ((new_cnt = bd->inbufBitCount - hufGroup->maxLen) < 0) {
  391                 /* bd->inbufBitCount < hufGroup->maxLen */
  392                 if (bd->inbufPos == bd->inbufCount) {
  393                     nextSym = get_bits(bd, hufGroup->maxLen);
  394                     goto got_huff_bits;
  395                 }
  396                 bd->inbufBits = (bd->inbufBits << 8) | bd->inbuf[bd->inbufPos++];
  397                 bd->inbufBitCount += 8;
  398             };
  399             bd->inbufBitCount = new_cnt; /* "bd->inbufBitCount -= hufGroup->maxLen;" */
  400             nextSym = (bd->inbufBits >> new_cnt) & ((1 << hufGroup->maxLen) - 1);
  401  got_huff_bits: ;
  402         } else { /* unoptimized equivalent */
  403             nextSym = get_bits(bd, hufGroup->maxLen);
  404         }
  405         /* Figure how many bits are in next symbol and unget extras */
  406         i = hufGroup->minLen;
  407         while (nextSym > limit[i]) ++i;
  408         j = hufGroup->maxLen - i;
  409         if (j < 0)
  410             return RETVAL_DATA_ERROR;
  411         bd->inbufBitCount += j;
  412 
  413         /* Huffman decode value to get nextSym (with bounds checking) */
  414         nextSym = (nextSym >> j) - base[i];
  415         if ((unsigned)nextSym >= MAX_SYMBOLS)
  416             return RETVAL_DATA_ERROR;
  417         nextSym = hufGroup->permute[nextSym];
  418 
  419         /* We have now decoded the symbol, which indicates either a new literal
  420            byte, or a repeated run of the most recent literal byte.  First,
  421            check if nextSym indicates a repeated run, and if so loop collecting
  422            how many times to repeat the last literal. */
  423         if ((unsigned)nextSym <= SYMBOL_RUNB) { /* RUNA or RUNB */
  424 
  425             /* If this is the start of a new run, zero out counter */
  426             if (runPos == 0) {
  427                 runPos = 1;
  428                 runCnt = 0;
  429             }
  430 
  431             /* Neat trick that saves 1 symbol: instead of or-ing 0 or 1 at
  432                each bit position, add 1 or 2 instead.  For example,
  433                1011 is 1<<0 + 1<<1 + 2<<2.  1010 is 2<<0 + 2<<1 + 1<<2.
  434                You can make any bit pattern that way using 1 less symbol than
  435                the basic or 0/1 method (except all bits 0, which would use no
  436                symbols, but a run of length 0 doesn't mean anything in this
  437                context).  Thus space is saved. */
  438             runCnt += (runPos << nextSym); /* +runPos if RUNA; +2*runPos if RUNB */
  439             if (runPos < dbufSize) runPos <<= 1;
  440             goto end_of_huffman_loop;
  441         }
  442 
  443         /* When we hit the first non-run symbol after a run, we now know
  444            how many times to repeat the last literal, so append that many
  445            copies to our buffer of decoded symbols (dbuf) now.  (The last
  446            literal used is the one at the head of the mtfSymbol array.) */
  447         if (runPos != 0) {
  448             uint8_t tmp_byte;
  449             if (dbufCount + runCnt > dbufSize) {
  450                 dbg("dbufCount:%d+runCnt:%d %d > dbufSize:%d RETVAL_DATA_ERROR",
  451                         dbufCount, runCnt, dbufCount + runCnt, dbufSize);
  452                 return RETVAL_DATA_ERROR;
  453             }
  454             tmp_byte = symToByte[mtfSymbol[0]];
  455             byteCount[tmp_byte] += runCnt;
  456             while (--runCnt >= 0) dbuf[dbufCount++] = (uint32_t)tmp_byte;
  457             runPos = 0;
  458         }
  459 
  460         /* Is this the terminating symbol? */
  461         if (nextSym > symTotal) break;
  462 
  463         /* At this point, nextSym indicates a new literal character.  Subtract
  464            one to get the position in the MTF array at which this literal is
  465            currently to be found.  (Note that the result can't be -1 or 0,
  466            because 0 and 1 are RUNA and RUNB.  But another instance of the
  467            first symbol in the mtf array, position 0, would have been handled
  468            as part of a run above.  Therefore 1 unused mtf position minus
  469            2 non-literal nextSym values equals -1.) */
  470         if (dbufCount >= dbufSize) return RETVAL_DATA_ERROR;
  471         i = nextSym - 1;
  472         uc = mtfSymbol[i];
  473 
  474         /* Adjust the MTF array.  Since we typically expect to move only a
  475          * small number of symbols, and are bound by 256 in any case, using
  476          * memmove here would typically be bigger and slower due to function
  477          * call overhead and other assorted setup costs. */
  478         do {
  479             mtfSymbol[i] = mtfSymbol[i-1];
  480         } while (--i);
  481         mtfSymbol[0] = uc;
  482         uc = symToByte[uc];
  483 
  484         /* We have our literal byte.  Save it into dbuf. */
  485         byteCount[uc]++;
  486         dbuf[dbufCount++] = (uint32_t)uc;
  487 
  488         /* Skip group initialization if we're not done with this group.  Done
  489          * this way to avoid compiler warning. */
  490  end_of_huffman_loop:
  491         if (--symCount >= 0) goto continue_this_group;
  492     }
  493 
  494     /* At this point, we've read all the Huffman-coded symbols (and repeated
  495        runs) for this block from the input stream, and decoded them into the
  496        intermediate buffer.  There are dbufCount many decoded bytes in dbuf[].
  497        Now undo the Burrows-Wheeler transform on dbuf.
  498        See http://dogma.net/markn/articles/bwt/bwt.htm
  499      */
  500 
  501     /* Turn byteCount into cumulative occurrence counts of 0 to n-1. */
  502     j = 0;
  503     for (i = 0; i < 256; i++) {
  504         int tmp_count = j + byteCount[i];
  505         byteCount[i] = j;
  506         j = tmp_count;
  507     }
  508 
  509     /* Figure out what order dbuf would be in if we sorted it. */
  510     for (i = 0; i < dbufCount; i++) {
  511         uint8_t tmp_byte = (uint8_t)dbuf[i];
  512         int tmp_count = byteCount[tmp_byte];
  513         dbuf[tmp_count] |= (i << 8);
  514         byteCount[tmp_byte] = tmp_count + 1;
  515     }
  516 
  517     /* Decode first byte by hand to initialize "previous" byte.  Note that it
  518        doesn't get output, and if the first three characters are identical
  519        it doesn't qualify as a run (hence writeRunCountdown=5). */
  520     if (dbufCount) {
  521         uint32_t tmp;
  522         if ((int)origPtr >= dbufCount) return RETVAL_DATA_ERROR;
  523         tmp = dbuf[origPtr];
  524         bd->writeCurrent = (uint8_t)tmp;
  525         bd->writePos = (tmp >> 8);
  526         bd->writeRunCountdown = 5;
  527     }
  528     bd->writeCount = dbufCount;
  529 
  530     return RETVAL_OK;
  531 }
  532 
  533 /* Undo Burrows-Wheeler transform on intermediate buffer to produce output.
  534    If start_bunzip was initialized with out_fd=-1, then up to len bytes of
  535    data are written to outbuf.  Return value is number of bytes written or
  536    error (all errors are negative numbers).  If out_fd!=-1, outbuf and len
  537    are ignored, data is written to out_fd and return is RETVAL_OK or error.
  538 
  539    NB: read_bunzip returns < 0 on error, or the number of *unfilled* bytes
  540    in outbuf. IOW: on EOF returns len ("all bytes are not filled"), not 0.
  541    (Why? This allows to get rid of one local variable)
  542 */
  543 int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
  544 {
  545     const uint32_t *dbuf;
  546     int pos, current, previous;
  547     uint32_t CRC;
  548 
  549     /* If we already have error/end indicator, return it */
  550     if (bd->writeCount < 0)
  551         return bd->writeCount;
  552 
  553     dbuf = bd->dbuf;
  554 
  555     /* Register-cached state (hopefully): */
  556     pos = bd->writePos;
  557     current = bd->writeCurrent;
  558     CRC = bd->writeCRC; /* small loss on x86-32 (not enough regs), win on x86-64 */
  559 
  560     /* We will always have pending decoded data to write into the output
  561        buffer unless this is the very first call (in which case we haven't
  562        Huffman-decoded a block into the intermediate buffer yet). */
  563     if (bd->writeCopies) {
  564 
  565  dec_writeCopies:
  566         /* Inside the loop, writeCopies means extra copies (beyond 1) */
  567         --bd->writeCopies;
  568 
  569         /* Loop outputting bytes */
  570         for (;;) {
  571 
  572             /* If the output buffer is full, save cached state and return */
  573             if (--len < 0) {
  574                 /* Unlikely branch.
  575                  * Use of "goto" instead of keeping code here
  576                  * helps compiler to realize this. */
  577                 goto outbuf_full;
  578             }
  579 
  580             /* Write next byte into output buffer, updating CRC */
  581             *outbuf++ = current;
  582             CRC = (CRC << 8) ^ bd->crc32Table[(CRC >> 24) ^ current];
  583 
  584             /* Loop now if we're outputting multiple copies of this byte */
  585             if (bd->writeCopies) {
  586                 /* Unlikely branch */
  587                 /*--bd->writeCopies;*/
  588                 /*continue;*/
  589                 /* Same, but (ab)using other existing --writeCopies operation
  590                  * (and this if() compiles into just test+branch pair): */
  591                 goto dec_writeCopies;
  592             }
  593  decode_next_byte:
  594             if (--bd->writeCount < 0)
  595                 break; /* input block is fully consumed, need next one */
  596 
  597             /* Follow sequence vector to undo Burrows-Wheeler transform */
  598             previous = current;
  599             pos = dbuf[pos];
  600             current = (uint8_t)pos;
  601             pos >>= 8;
  602 
  603             /* After 3 consecutive copies of the same byte, the 4th
  604              * is a repeat count.  We count down from 4 instead
  605              * of counting up because testing for non-zero is faster */
  606             if (--bd->writeRunCountdown != 0) {
  607                 if (current != previous)
  608                     bd->writeRunCountdown = 4;
  609             } else {
  610                 /* Unlikely branch */
  611                 /* We have a repeated run, this byte indicates the count */
  612                 bd->writeCopies = current;
  613                 current = previous;
  614                 bd->writeRunCountdown = 5;
  615 
  616                 /* Sometimes there are just 3 bytes (run length 0) */
  617                 if (!bd->writeCopies) goto decode_next_byte;
  618 
  619                 /* Subtract the 1 copy we'd output anyway to get extras */
  620                 --bd->writeCopies;
  621             }
  622         } /* for(;;) */
  623 
  624         /* Decompression of this input block completed successfully */
  625         bd->writeCRC = CRC = ~CRC;
  626         bd->totalCRC = ((bd->totalCRC << 1) | (bd->totalCRC >> 31)) ^ CRC;
  627 
  628         /* If this block had a CRC error, force file level CRC error */
  629         if (CRC != bd->headerCRC) {
  630             bd->totalCRC = bd->headerCRC + 1;
  631             return RETVAL_LAST_BLOCK;
  632         }
  633     }
  634 
  635     /* Refill the intermediate buffer by Huffman-decoding next block of input */
  636     {
  637         int r = get_next_block(bd);
  638         if (r) { /* error/end */
  639             bd->writeCount = r;
  640             return (r != RETVAL_LAST_BLOCK) ? r : len;
  641         }
  642     }
  643 
  644     CRC = ~0;
  645     pos = bd->writePos;
  646     current = bd->writeCurrent;
  647     goto decode_next_byte;
  648 
  649  outbuf_full:
  650     /* Output buffer is full, save cached state and return */
  651     bd->writePos = pos;
  652     bd->writeCurrent = current;
  653     bd->writeCRC = CRC;
  654 
  655     bd->writeCopies++;
  656 
  657     return 0;
  658 }
  659 
  660 /* Allocate the structure, read file header.  If in_fd==-1, inbuf must contain
  661    a complete bunzip file (len bytes long).  If in_fd!=-1, inbuf and len are
  662    ignored, and data is read from file handle into temporary buffer. */
  663 
  664 /* Because bunzip2 is used for help text unpacking, and because bb_show_usage()
  665    should work for NOFORK applets too, we must be extremely careful to not leak
  666    any allocations! */
  667 int FAST_FUNC start_bunzip(bunzip_data **bdp, int in_fd,
  668         const void *inbuf, int len)
  669 {
  670     bunzip_data *bd;
  671     unsigned i;
  672     enum {
  673         BZh0 = ('B' << 24) + ('Z' << 16) + ('h' << 8) + '0',
  674         h0 = ('h' << 8) + '0',
  675     };
  676 
  677     /* Figure out how much data to allocate */
  678     i = sizeof(bunzip_data);
  679     if (in_fd != -1) i += IOBUF_SIZE;
  680 
  681     /* Allocate bunzip_data.  Most fields initialize to zero. */
  682     bd = *bdp = xzalloc(i);
  683     if (bd == NULL)
  684         return -1;
  685 
  686     /* Setup input buffer */
  687     bd->in_fd = in_fd;
  688     if (-1 == in_fd) {
  689         /* in this case, bd->inbuf is read-only */
  690         bd->inbuf = (void*)inbuf; /* cast away const-ness */
  691     } else {
  692         bd->inbuf = (uint8_t*)(bd + 1);
  693         memcpy(bd->inbuf, inbuf, len);
  694     }
  695     bd->inbufCount = len;
  696 
  697     /* Init the CRC32 table (big endian) */
  698     crc32_filltable(bd->crc32Table, 1);
  699 
  700     /* Setup for I/O error handling via longjmp */
  701     i = setjmp(bd->jmpbuf);
  702     if (i) return i;
  703 
  704     /* Ensure that file starts with "BZh['1'-'9']." */
  705     /* Update: now caller verifies 1st two bytes, makes .gz/.bz2
  706      * integration easier */
  707     /* was: */
  708     /* i = get_bits(bd, 32); */
  709     /* if ((unsigned)(i - BZh0 - 1) >= 9) return RETVAL_NOT_BZIP_DATA; */
  710     i = get_bits(bd, 16);
  711     if ((unsigned)(i - h0 - 1) >= 9) return RETVAL_NOT_BZIP_DATA;
  712 
  713     /* Fourth byte (ascii '1'-'9') indicates block size in units of 100k of
  714        uncompressed data.  Allocate intermediate buffer for block. */
  715     /* bd->dbufSize = 100000 * (i - BZh0); */
  716     bd->dbufSize = 100000 * (i - h0);
  717 
  718     /* Cannot use xmalloc - may leak bd in NOFORK case! */
  719     bd->dbuf = malloc_or_warn(bd->dbufSize * sizeof(bd->dbuf[0]));
  720     if (!bd->dbuf) {
  721         free(bd);
  722         xfunc_die();
  723     }
  724     return RETVAL_OK;
  725 }
  726 
  727 void FAST_FUNC dealloc_bunzip(bunzip_data *bd)
  728 {
  729     free(bd->dbuf);
  730     free(bd);
  731 }
  732 
  733 
  734 /* Decompress src_fd to dst_fd.  Stops at end of bzip data, not end of file. */
  735 IF_DESKTOP(long long) int FAST_FUNC
  736 unpack_bz2_stream(transformer_state_t *xstate)
  737 {
  738     IF_DESKTOP(long long total_written = 0;)
  739     bunzip_data *bd;
  740     char *outbuf;
  741     int i, nwrote;
  742     unsigned len;
  743 
  744     if (check_signature16(xstate, BZIP2_MAGIC))
  745         return -1;
  746 
  747     outbuf = xmalloc(IOBUF_SIZE);
  748     if (outbuf == NULL)
  749         return -1;
  750     len = 0;
  751     while (1) { /* "Process one BZ... stream" loop */
  752 
  753         i = start_bunzip(&bd, xstate->src_fd, outbuf + 2, len);
  754 
  755         if (i == 0) {
  756             while (1) { /* "Produce some output bytes" loop */
  757                 i = read_bunzip(bd, outbuf, IOBUF_SIZE);
  758                 if (i < 0) /* error? */
  759                     break;
  760                 i = IOBUF_SIZE - i; /* number of bytes produced */
  761                 if (i == 0) /* EOF? */
  762                     break;
  763                 nwrote = (int)transformer_write(xstate, outbuf, i);
  764                 if (nwrote != i) {
  765                     i = (nwrote == -ENOSPC)?(int)xstate->mem_output_size_max:RETVAL_SHORT_WRITE;
  766                     goto release_mem;
  767                 }
  768                 IF_DESKTOP(total_written += i;)
  769             }
  770         }
  771 
  772         if (i != RETVAL_LAST_BLOCK
  773         /* Observed case when i == RETVAL_OK:
  774          * "bzcat z.bz2", where "z.bz2" is a bzipped zero-length file
  775          * (to be exact, z.bz2 is exactly these 14 bytes:
  776          * 42 5a 68 39 17 72 45 38  50 90 00 00 00 00).
  777          */
  778          && i != RETVAL_OK
  779         ) {
  780             bb_error_msg("bunzip error %d", i);
  781             break;
  782         }
  783         if (bd->headerCRC != bd->totalCRC) {
  784             bb_error_msg("CRC error");
  785             break;
  786         }
  787 
  788         /* Successfully unpacked one BZ stream */
  789         i = RETVAL_OK;
  790 
  791         /* Do we have "BZ..." after last processed byte?
  792          * pbzip2 (parallelized bzip2) produces such files.
  793          */
  794         len = bd->inbufCount - bd->inbufPos;
  795         memcpy(outbuf, &bd->inbuf[bd->inbufPos], len);
  796         if (len < 2) {
  797             if (safe_read(xstate->src_fd, outbuf + len, 2 - len) != 2 - len)
  798                 break;
  799             len = 2;
  800         }
  801         if (*(uint16_t*)outbuf != BZIP2_MAGIC) /* "BZ"? */
  802             break;
  803         dealloc_bunzip(bd);
  804         len -= 2;
  805     }
  806 
  807  release_mem:
  808     dealloc_bunzip(bd);
  809     free(outbuf);
  810 
  811     return i ? i : IF_DESKTOP(total_written) + 0;
  812 }
  813 
  814 #ifdef TESTING
  815 
  816 static char *const bunzip_errors[] = {
  817     NULL, "Bad file checksum", "Not bzip data",
  818     "Unexpected input EOF", "Unexpected output EOF", "Data error",
  819     "Out of memory", "Obsolete (pre 0.9.5) bzip format not supported"
  820 };
  821 
  822 /* Dumb little test thing, decompress stdin to stdout */
  823 int main(int argc, char **argv)
  824 {
  825     char c;
  826 
  827     int i = unpack_bz2_stream(0, 1);
  828     if (i < 0)
  829         fprintf(stderr, "%s\n", bunzip_errors[-i]);
  830     else if (read(STDIN_FILENO, &c, 1))
  831         fprintf(stderr, "Trailing garbage ignored\n");
  832     return -i;
  833 }
  834 #endif