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/* inftree9.c -- generate Huffman trees for efficient decoding |
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* Copyright (C) 1995-2026 Mark Adler |
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* For conditions of distribution and use, see copyright notice in zlib.h |
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*/ |
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#include "zutil.h" |
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#include "inftree9.h" |
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#define MAXBITS 15 |
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const char inflate9_copyright[] = |
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" inflate9 1.3.2 Copyright 1995-2026 Mark Adler "; |
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/* |
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If you use the zlib library in a product, an acknowledgment is welcome |
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in the documentation of your product. If for some reason you cannot |
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include such an acknowledgment, I would appreciate that you keep this |
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copyright string in the executable of your product. |
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*/ |
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/* |
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Build a set of tables to decode the provided canonical Huffman code. |
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The code lengths are lens[0..codes-1]. The result starts at *table, |
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whose indices are 0..2^bits-1. work is a writable array of at least |
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lens shorts, which is used as a work area. type is the type of code |
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to be generated, CODES, LENS, or DISTS. On return, zero is success, |
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-1 is an invalid code, and +1 means that ENOUGH isn't enough. table |
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on return points to the next available entry's address. bits is the |
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requested root table index bits, and on return it is the actual root |
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table index bits. It will differ if the request is greater than the |
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longest code or if it is less than the shortest code. |
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*/ |
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int inflate_table9(codetype type, unsigned short FAR *lens, unsigned codes, |
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code FAR * FAR *table, unsigned FAR *bits, |
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unsigned short FAR *work) { |
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unsigned len; /* a code's length in bits */ |
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unsigned sym; /* index of code symbols */ |
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unsigned min, max; /* minimum and maximum code lengths */ |
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unsigned root; /* number of index bits for root table */ |
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unsigned curr; /* number of index bits for current table */ |
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unsigned drop; /* code bits to drop for sub-table */ |
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int left; /* number of prefix codes available */ |
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unsigned used; /* code entries in table used */ |
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unsigned huff; /* Huffman code */ |
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unsigned incr; /* for incrementing code, index */ |
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unsigned fill; /* index for replicating entries */ |
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unsigned low; /* low bits for current root entry */ |
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unsigned mask; /* mask for low root bits */ |
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code this; /* table entry for duplication */ |
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code FAR *next; /* next available space in table */ |
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const unsigned short FAR *base; /* base value table to use */ |
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const unsigned short FAR *extra; /* extra bits table to use */ |
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int end; /* use base and extra for symbol > end */ |
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unsigned short count[MAXBITS+1]; /* number of codes of each length */ |
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unsigned short offs[MAXBITS+1]; /* offsets in table for each length */ |
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static const unsigned short lbase[31] = { /* Length codes 257..285 base */ |
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3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 15, 17, |
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19, 23, 27, 31, 35, 43, 51, 59, 67, 83, 99, 115, |
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131, 163, 195, 227, 3, 0, 0}; |
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static const unsigned short lext[31] = { /* Length codes 257..285 extra */ |
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128, 128, 128, 128, 128, 128, 128, 128, 129, 129, 129, 129, |
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130, 130, 130, 130, 131, 131, 131, 131, 132, 132, 132, 132, |
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133, 133, 133, 133, 144, 199, 75}; |
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static const unsigned short dbase[32] = { /* Distance codes 0..31 base */ |
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1, 2, 3, 4, 5, 7, 9, 13, 17, 25, 33, 49, |
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65, 97, 129, 193, 257, 385, 513, 769, 1025, 1537, 2049, 3073, |
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4097, 6145, 8193, 12289, 16385, 24577, 32769, 49153}; |
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static const unsigned short dext[32] = { /* Distance codes 0..31 extra */ |
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128, 128, 128, 128, 129, 129, 130, 130, 131, 131, 132, 132, |
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133, 133, 134, 134, 135, 135, 136, 136, 137, 137, 138, 138, |
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139, 139, 140, 140, 141, 141, 142, 142}; |
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/* |
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Process a set of code lengths to create a canonical Huffman code. The |
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code lengths are lens[0..codes-1]. Each length corresponds to the |
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symbols 0..codes-1. The Huffman code is generated by first sorting the |
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symbols by length from short to long, and retaining the symbol order |
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for codes with equal lengths. Then the code starts with all zero bits |
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for the first code of the shortest length, and the codes are integer |
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increments for the same length, and zeros are appended as the length |
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increases. For the deflate format, these bits are stored backwards |
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from their more natural integer increment ordering, and so when the |
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decoding tables are built in the large loop below, the integer codes |
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are incremented backwards. |
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This routine assumes, but does not check, that all of the entries in |
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lens[] are in the range 0..MAXBITS. The caller must assure this. |
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1..MAXBITS is interpreted as that code length. zero means that that |
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symbol does not occur in this code. |
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The codes are sorted by computing a count of codes for each length, |
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creating from that a table of starting indices for each length in the |
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sorted table, and then entering the symbols in order in the sorted |
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table. The sorted table is work[], with that space being provided by |
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the caller. |
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The length counts are used for other purposes as well, i.e. finding |
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the minimum and maximum length codes, determining if there are any |
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codes at all, checking for a valid set of lengths, and looking ahead |
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at length counts to determine sub-table sizes when building the |
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decoding tables. |
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*/ |
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/* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ |
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for (len = 0; len <= MAXBITS; len++) |
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count[len] = 0; |
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for (sym = 0; sym < codes; sym++) |
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count[lens[sym]]++; |
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/* bound code lengths, force root to be within code lengths */ |
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root = *bits; |
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for (max = MAXBITS; max >= 1; max--) |
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if (count[max] != 0) break; |
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if (root > max) root = max; |
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if (max == 0) return -1; /* no codes! */ |
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for (min = 1; min <= MAXBITS; min++) |
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if (count[min] != 0) break; |
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if (root < min) root = min; |
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/* check for an over-subscribed or incomplete set of lengths */ |
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left = 1; |
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for (len = 1; len <= MAXBITS; len++) { |
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left <<= 1; |
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left -= count[len]; |
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if (left < 0) return -1; /* over-subscribed */ |
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} |
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if (left > 0 && (type == CODES || max != 1)) |
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return -1; /* incomplete set */ |
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/* generate offsets into symbol table for each length for sorting */ |
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offs[1] = 0; |
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for (len = 1; len < MAXBITS; len++) |
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offs[len + 1] = offs[len] + count[len]; |
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/* sort symbols by length, by symbol order within each length */ |
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for (sym = 0; sym < codes; sym++) |
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if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; |
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/* |
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Create and fill in decoding tables. In this loop, the table being |
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filled is at next and has curr index bits. The code being used is huff |
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with length len. That code is converted to an index by dropping drop |
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bits off of the bottom. For codes where len is less than drop + curr, |
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those top drop + curr - len bits are incremented through all values to |
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fill the table with replicated entries. |
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root is the number of index bits for the root table. When len exceeds |
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root, sub-tables are created pointed to by the root entry with an index |
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of the low root bits of huff. This is saved in low to check for when a |
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new sub-table should be started. drop is zero when the root table is |
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being filled, and drop is root when sub-tables are being filled. |
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When a new sub-table is needed, it is necessary to look ahead in the |
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code lengths to determine what size sub-table is needed. The length |
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counts are used for this, and so count[] is decremented as codes are |
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entered in the tables. |
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used keeps track of how many table entries have been allocated from the |
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provided *table space. It is checked for LENS and DIST tables against |
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the constants ENOUGH_LENS and ENOUGH_DISTS to guard against changes in |
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the initial root table size constants. See the comments in inftree9.h |
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for more information. |
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sym increments through all symbols, and the loop terminates when |
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all codes of length max, i.e. all codes, have been processed. This |
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routine permits incomplete codes, so another loop after this one fills |
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in the rest of the decoding tables with invalid code markers. |
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*/ |
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/* set up for code type */ |
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switch (type) { |
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case CODES: |
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base = extra = work; /* dummy value--not used */ |
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end = 19; |
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break; |
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case LENS: |
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base = lbase; |
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base -= 257; |
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extra = lext; |
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extra -= 257; |
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end = 256; |
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break; |
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default: /* DISTS */ |
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base = dbase; |
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extra = dext; |
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end = -1; |
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} |
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/* initialize state for loop */ |
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huff = 0; /* starting code */ |
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sym = 0; /* starting code symbol */ |
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len = min; /* starting code length */ |
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next = *table; /* current table to fill in */ |
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curr = root; /* current table index bits */ |
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drop = 0; /* current bits to drop from code for index */ |
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low = (unsigned)(-1); /* trigger new sub-table when len > root */ |
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used = 1U << root; /* use root table entries */ |
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mask = used - 1; /* mask for comparing low */ |
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/* check available table space */ |
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if ((type == LENS && used >= ENOUGH_LENS) || |
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(type == DISTS && used >= ENOUGH_DISTS)) |
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return 1; |
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/* process all codes and make table entries */ |
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for (;;) { |
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/* create table entry */ |
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this.bits = (unsigned char)(len - drop); |
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if ((int)(work[sym]) < end) { |
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this.op = (unsigned char)0; |
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this.val = work[sym]; |
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} |
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else if ((int)(work[sym]) > end) { |
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this.op = (unsigned char)(extra[work[sym]]); |
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this.val = base[work[sym]]; |
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} |
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else { |
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this.op = (unsigned char)(32 + 64); /* end of block */ |
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this.val = 0; |
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} |
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/* replicate for those indices with low len bits equal to huff */ |
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incr = 1U << (len - drop); |
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fill = 1U << curr; |
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do { |
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fill -= incr; |
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next[(huff >> drop) + fill] = this; |
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} while (fill != 0); |
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/* backwards increment the len-bit code huff */ |
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incr = 1U << (len - 1); |
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while (huff & incr) |
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incr >>= 1; |
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if (incr != 0) { |
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huff &= incr - 1; |
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huff += incr; |
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} |
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else |
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huff = 0; |
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/* go to next symbol, update count, len */ |
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sym++; |
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if (--(count[len]) == 0) { |
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if (len == max) break; |
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len = lens[work[sym]]; |
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} |
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/* create new sub-table if needed */ |
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if (len > root && (huff & mask) != low) { |
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/* if first time, transition to sub-tables */ |
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if (drop == 0) |
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drop = root; |
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/* increment past last table */ |
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next += 1U << curr; |
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/* determine length of next table */ |
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curr = len - drop; |
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left = (int)(1 << curr); |
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while (curr + drop < max) { |
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left -= count[curr + drop]; |
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if (left <= 0) break; |
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curr++; |
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left <<= 1; |
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} |
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/* check for enough space */ |
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used += 1U << curr; |
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if ((type == LENS && used >= ENOUGH_LENS) || |
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(type == DISTS && used >= ENOUGH_DISTS)) |
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return 1; |
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/* point entry in root table to sub-table */ |
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low = huff & mask; |
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(*table)[low].op = (unsigned char)curr; |
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(*table)[low].bits = (unsigned char)root; |
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(*table)[low].val = (unsigned short)(next - *table); |
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} |
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} |
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/* |
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Fill in rest of table for incomplete codes. This loop is similar to the |
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loop above in incrementing huff for table indices. It is assumed that |
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len is equal to curr + drop, so there is no loop needed to increment |
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through high index bits. When the current sub-table is filled, the loop |
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drops back to the root table to fill in any remaining entries there. |
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*/ |
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this.op = (unsigned char)64; /* invalid code marker */ |
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this.bits = (unsigned char)(len - drop); |
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this.val = (unsigned short)0; |
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while (huff != 0) { |
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/* when done with sub-table, drop back to root table */ |
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if (drop != 0 && (huff & mask) != low) { |
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drop = 0; |
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len = root; |
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next = *table; |
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curr = root; |
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this.bits = (unsigned char)len; |
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} |
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/* put invalid code marker in table */ |
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next[huff >> drop] = this; |
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/* backwards increment the len-bit code huff */ |
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incr = 1U << (len - 1); |
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while (huff & incr) |
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incr >>= 1; |
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if (incr != 0) { |
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huff &= incr - 1; |
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huff += incr; |
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} |
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else |
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huff = 0; |
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} |
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/* set return parameters */ |
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*table += used; |
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*bits = root; |
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return 0; |
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} |
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