/* Small bzip2 deflate implementation, by Rob Landley (rob@landley.net). Based on 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. This code is licensed under the LGPLv2: 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 https://www.hospiceacadiana.com/ Manuel */ /* Made it fit for running in Linux Kernel by Alain Knaff (alain@knaff.lu)*/ #ifdef STATIC#define PREBOOT#else#include <linux/decompress/bunzip2.h>#endif /* STATIC */ #include <linux/decompress/mm.h>#include <linux/crc32poly.h> #ifndef INT_MAX#define INT_MAX 0x7fffffff#endif /* 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 /* Status return values */#define RETVAL_OK 0#define RETVAL_LAST_BLOCK (-1)#define RETVAL_NOT_BZIP_DATA (-2)#define RETVAL_UNEXPECTED_INPUT_EOF (-3)#define RETVAL_UNEXPECTED_OUTPUT_EOF (-4)#define RETVAL_DATA_ERROR (-5)#define RETVAL_OUT_OF_MEMORY (-6)#define RETVAL_OBSOLETE_INPUT (-7) /* Other housekeeping constants */#define BZIP2_IOBUF_SIZE 4096 /* 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 sentinel value. */ int limit[MAX_HUFCODE_BITS+1]; int base[MAX_HUFCODE_BITS]; int permute[MAX_SYMBOLS]; int minLen, maxLen;}; /* Structure holding all the housekeeping data, including IO buffers and memory that persists between calls to bunzip */struct bunzip_data { /* State for interrupting output loop */ int writeCopies, writePos, writeRunCountdown, writeCount, writeCurrent; /* I/O tracking data (file handles, buffers, positions, etc.) */ long (*fill)(void*, unsigned long); long inbufCount, inbufPos /*, outbufPos*/; unsigned char *inbuf /*,*outbuf*/; unsigned int inbufBitCount, inbufBits; /* The CRC values stored in the block header and calculated from the data */ unsigned int crc32Table[256], headerCRC, totalCRC, writeCRC; /* Intermediate buffer and its size (in bytes) */ unsigned int *dbuf, dbufSize; /* 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 */ int io_error; /* non-zero if we have IO error */ int byteCount[256]; unsigned char symToByte[256], mtfSymbol[256];}; /* 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 INIT 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 (bd->io_error) return 0; bd->inbufCount = bd->fill(bd->inbuf, BZIP2_IOBUF_SIZE); if (bd->inbufCount <= 0) { bd->io_error = RETVAL_UNEXPECTED_INPUT_EOF; return 0; } bd->inbufPos = 0; } /* Avoid 32-bit overflow (dump bit buffer to top of output) */ if (bd->inbufBitCount >= 24) { bits = bd->inbufBits & ((1ULL << 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) & ((1ULL << bits_wanted) - 1); return bits;} /* Unpacks the next block and sets up for the inverse burrows-wheeler step. */ static int INIT get_next_block(struct bunzip_data *bd){ struct group_data *hufGroup = NULL; int *base = NULL; int *limit = NULL; int dbufCount, nextSym, dbufSize, groupCount, selector, i, j, k, t, runPos, symCount, symTotal, nSelectors, *byteCount; unsigned char uc, *symToByte, *mtfSymbol, *selectors; unsigned int *dbuf, origPtr; dbuf = bd->dbuf; dbufSize = bd->dbufSize; selectors = bd->selectors; byteCount = bd->byteCount; symToByte = bd->symToByte; mtfSymbol = bd->mtfSymbol; /* 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. */ if (get_bits(bd, 1)) return RETVAL_OBSOLETE_INPUT; origPtr = get_bits(bd, 24); if (origPtr >= 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. */ t = get_bits(bd, 16); symTotal = 0; for (i = 0; i < 16; i++) { if (t&(1 << (15-i))) { k = get_bits(bd, 16); for (j = 0; j < 16; j++) if (k&(1 << (15-j))) symToByte[symTotal++] = (16*i)+j; } } /* How many different Huffman coding groups does this block use? */ groupCount = get_bits(bd, 3); 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. (MTF = Move To Front, as each value is used it's moved to the start of the list.) */ nSelectors = get_bits(bd, 15); if (!nSelectors) return RETVAL_DATA_ERROR; for (i = 0; i < groupCount; i++) mtfSymbol[i] = i; for (i = 0; i < nSelectors; i++) { /* Get next value */ 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]; 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 literal symbols, plus two run symbols (RUNA, RUNB) */ symCount = symTotal+2; for (j = 0; j < groupCount; j++) { unsigned char length[MAX_SYMBOLS]; unsigned short temp[MAX_HUFCODE_BITS+1]; int minLen, maxLen, pp; /* 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 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); } /* 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]; for (i = 1; i < symCount; i++) { if (length[i] > maxLen) maxLen = length[i]; else if (length[i] < minLen) minLen = length[i]; } /* Calculate permute[], base[], and limit[] tables from * length[]. * * permute[] is the lookup table for converting * Huffman coded symbols into decoded symbols. 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. 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; 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; /* Calculate permute[]. Concurrently, 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 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 *minus the cumulative count of symbols coded for *already). */ pp = t = 0; for (i = minLen; i < maxLen; i++) { pp += temp[i]; /* 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]); } limit[maxLen+1] = INT_MAX; /* Sentinel value for * reading next sym. */ limit[maxLen] = pp+temp[maxLen]-1; base[minLen] = 0; } /* 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 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. */ if (!(symCount--)) { symCount = GROUP_SIZE-1; if (selector >= nSelectors) return RETVAL_DATA_ERROR; hufGroup = bd->groups+selectors[selector++]; base = hufGroup->base-1; limit = hufGroup->limit-1; } /* 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 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]; /* 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) { runPos = 1; t = 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. */ t += (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+t >= dbufSize) return RETVAL_DATA_ERROR; uc = symToByte[mtfSymbol[0]]; byteCount[uc] += t; while (t--) dbuf[dbufCount++] = uc; } /* Is this the terminating symbol? */ if (nextSym > symTotal) break; /* 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]; /* 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); mtfSymbol[0] = uc; uc = symToByte[uc]; /* We have our literal byte. Save it into dbuf. */ byteCount[uc]++; dbuf[dbufCount++] = (unsigned int)uc; } /* 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 */ /* Turn byteCount into cumulative occurrence counts of 0 to n-1. */ j = 0; for (i = 0; i < 256; i++) { k = j+byteCount[i]; byteCount[i] = j; j = k; } /* Figure out what order dbuf would be in if we sorted it. */ for (i = 0; i < dbufCount; i++) { uc = (unsigned char)(dbuf[i] & 0xff); dbuf[byteCount[uc]] |= (i << 8); byteCount[uc]++; } /* Decode first byte by hand to initialize "previous" byte.Lines 1–500 of 757. Load more
/* Small bzip2 deflate implementation, by Rob Landley (rob@landley.net). Based on 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. This code is licensed under the LGPLv2: 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 https://www.hospiceacadiana.com/ Manuel */ /* Made it fit for running in Linux Kernel by Alain Knaff (alain@knaff.lu) */ #ifdef STATIC #define PREBOOT #else #include <linux/decompress/bunzip2.h> #endif /* STATIC */ #include <linux/decompress/mm.h> #include <linux/crc32poly.h> #ifndef INT_MAX #define INT_MAX 0x7fffffff #endif /* 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 /* Status return values */ #define RETVAL_OK 0 #define RETVAL_LAST_BLOCK (-1) #define RETVAL_NOT_BZIP_DATA (-2) #define RETVAL_UNEXPECTED_INPUT_EOF (-3) #define RETVAL_UNEXPECTED_OUTPUT_EOF (-4) #define RETVAL_DATA_ERROR (-5) #define RETVAL_OUT_OF_MEMORY (-6) #define RETVAL_OBSOLETE_INPUT (-7) /* Other housekeeping constants */ #define BZIP2_IOBUF_SIZE 4096 /* 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 sentinel value. */ int limit[MAX_HUFCODE_BITS+1]; int base[MAX_HUFCODE_BITS]; int permute[MAX_SYMBOLS]; int minLen, maxLen; }; /* Structure holding all the housekeeping data, including IO buffers and memory that persists between calls to bunzip */ struct bunzip_data { /* State for interrupting output loop */ int writeCopies, writePos, writeRunCountdown, writeCount, writeCurrent; /* I/O tracking data (file handles, buffers, positions, etc.) */ long (*fill)(void*, unsigned long); long inbufCount, inbufPos /*, outbufPos*/; unsigned char *inbuf /*,*outbuf*/; unsigned int inbufBitCount, inbufBits; /* The CRC values stored in the block header and calculated from the data */ unsigned int crc32Table[256], headerCRC, totalCRC, writeCRC; /* Intermediate buffer and its size (in bytes) */ unsigned int *dbuf, dbufSize; /* 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 */ int io_error; /* non-zero if we have IO error */ int byteCount[256]; unsigned char symToByte[256], mtfSymbol[256]; }; /* 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 INIT 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 (bd->io_error) return 0; bd->inbufCount = bd->fill(bd->inbuf, BZIP2_IOBUF_SIZE); if (bd->inbufCount <= 0) { bd->io_error = RETVAL_UNEXPECTED_INPUT_EOF; return 0; } bd->inbufPos = 0; } /* Avoid 32-bit overflow (dump bit buffer to top of output) */ if (bd->inbufBitCount >= 24) { bits = bd->inbufBits & ((1ULL << 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) & ((1ULL << bits_wanted) - 1); return bits; } /* Unpacks the next block and sets up for the inverse burrows-wheeler step. */ static int INIT get_next_block(struct bunzip_data *bd) { struct group_data *hufGroup = NULL; int *base = NULL; int *limit = NULL; int dbufCount, nextSym, dbufSize, groupCount, selector, i, j, k, t, runPos, symCount, symTotal, nSelectors, *byteCount; unsigned char uc, *symToByte, *mtfSymbol, *selectors; unsigned int *dbuf, origPtr; dbuf = bd->dbuf; dbufSize = bd->dbufSize; selectors = bd->selectors; byteCount = bd->byteCount; symToByte = bd->symToByte; mtfSymbol = bd->mtfSymbol; /* 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. */ if (get_bits(bd, 1)) return RETVAL_OBSOLETE_INPUT; origPtr = get_bits(bd, 24); if (origPtr >= 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. */ t = get_bits(bd, 16); symTotal = 0; for (i = 0; i < 16; i++) { if (t&(1 << (15-i))) { k = get_bits(bd, 16); for (j = 0; j < 16; j++) if (k&(1 << (15-j))) symToByte[symTotal++] = (16*i)+j; } } /* How many different Huffman coding groups does this block use? */ groupCount = get_bits(bd, 3); 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. (MTF = Move To Front, as each value is used it's moved to the start of the list.) */ nSelectors = get_bits(bd, 15); if (!nSelectors) return RETVAL_DATA_ERROR; for (i = 0; i < groupCount; i++) mtfSymbol[i] = i; for (i = 0; i < nSelectors; i++) { /* Get next value */ 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]; 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 literal symbols, plus two run symbols (RUNA, RUNB) */ symCount = symTotal+2; for (j = 0; j < groupCount; j++) { unsigned char length[MAX_SYMBOLS]; unsigned short temp[MAX_HUFCODE_BITS+1]; int minLen, maxLen, pp; /* 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 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); } /* 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]; for (i = 1; i < symCount; i++) { if (length[i] > maxLen) maxLen = length[i]; else if (length[i] < minLen) minLen = length[i]; } /* Calculate permute[], base[], and limit[] tables from * length[]. * * permute[] is the lookup table for converting * Huffman coded symbols into decoded symbols. 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. 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; 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; /* Calculate permute[]. Concurrently, 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 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 *minus the cumulative count of symbols coded for *already). */ pp = t = 0; for (i = minLen; i < maxLen; i++) { pp += temp[i]; /* 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]); } limit[maxLen+1] = INT_MAX; /* Sentinel value for * reading next sym. */ limit[maxLen] = pp+temp[maxLen]-1; base[minLen] = 0; } /* 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 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. */ if (!(symCount--)) { symCount = GROUP_SIZE-1; if (selector >= nSelectors) return RETVAL_DATA_ERROR; hufGroup = bd->groups+selectors[selector++]; base = hufGroup->base-1; limit = hufGroup->limit-1; } /* 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 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]; /* 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) { runPos = 1; t = 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. */ t += (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+t >= dbufSize) return RETVAL_DATA_ERROR; uc = symToByte[mtfSymbol[0]]; byteCount[uc] += t; while (t--) dbuf[dbufCount++] = uc; } /* Is this the terminating symbol? */ if (nextSym > symTotal) break; /* 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]; /* 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); mtfSymbol[0] = uc; uc = symToByte[uc]; /* We have our literal byte. Save it into dbuf. */ byteCount[uc]++; dbuf[dbufCount++] = (unsigned int)uc; } /* 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 */ /* Turn byteCount into cumulative occurrence counts of 0 to n-1. */ j = 0; for (i = 0; i < 256; i++) { k = j+byteCount[i]; byteCount[i] = j; j = k; } /* Figure out what order dbuf would be in if we sorted it. */ for (i = 0; i < dbufCount; i++) { uc = (unsigned char)(dbuf[i] & 0xff); dbuf[byteCount[uc]] |= (i << 8); byteCount[uc]++; } /* Decode first byte by hand to initialize "previous" byte.