diff options
Diffstat (limited to 'dep/src/zlib/inftrees.c')
| -rw-r--r-- | dep/src/zlib/inftrees.c | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/dep/src/zlib/inftrees.c b/dep/src/zlib/inftrees.c index 821dabc5caa..8a9c13ff03d 100644 --- a/dep/src/zlib/inftrees.c +++ b/dep/src/zlib/inftrees.c @@ -2,9 +2,12 @@ * Copyright (C) 1995-2005 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h */ + #include "zutil.h" #include "inftrees.h" + #define MAXBITS 15 + const char inflate_copyright[] = " inflate 1.2.3 Copyright 1995-2005 Mark Adler "; /* @@ -13,6 +16,7 @@ const char inflate_copyright[] = include such an acknowledgment, I would appreciate that you keep this copyright string in the executable of your product. */ + /* Build a set of tables to decode the provided canonical Huffman code. The code lengths are lens[0..codes-1]. The result starts at *table, @@ -67,6 +71,7 @@ unsigned short FAR *work; 16, 16, 16, 16, 17, 17, 18, 18, 19, 19, 20, 20, 21, 21, 22, 22, 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 28, 28, 29, 29, 64, 64}; + /* Process a set of code lengths to create a canonical Huffman code. The code lengths are lens[0..codes-1]. Each length corresponds to the @@ -79,26 +84,31 @@ unsigned short FAR *work; from their more natural integer increment ordering, and so when the decoding tables are built in the large loop below, the integer codes are incremented backwards. + This routine assumes, but does not check, that all of the entries in lens[] are in the range 0..MAXBITS. The caller must assure this. 1..MAXBITS is interpreted as that code length. zero means that that symbol does not occur in this code. + The codes are sorted by computing a count of codes for each length, creating from that a table of starting indices for each length in the sorted table, and then entering the symbols in order in the sorted table. The sorted table is work[], with that space being provided by the caller. + The length counts are used for other purposes as well, i.e. finding the minimum and maximum length codes, determining if there are any codes at all, checking for a valid set of lengths, and looking ahead at length counts to determine sub-table sizes when building the decoding tables. */ + /* accumulate lengths for codes (assumes lens[] all in 0..MAXBITS) */ for (len = 0; len <= MAXBITS; len++) count[len] = 0; for (sym = 0; sym < codes; sym++) count[lens[sym]]++; + /* bound code lengths, force root to be within code lengths */ root = *bits; for (max = MAXBITS; max >= 1; max--) @@ -116,6 +126,7 @@ unsigned short FAR *work; for (min = 1; min <= MAXBITS; min++) if (count[min] != 0) break; if (root < min) root = min; + /* check for an over-subscribed or incomplete set of lengths */ left = 1; for (len = 1; len <= MAXBITS; len++) { @@ -125,13 +136,16 @@ unsigned short FAR *work; } if (left > 0 && (type == CODES || max != 1)) return -1; /* incomplete set */ + /* generate offsets into symbol table for each length for sorting */ offs[1] = 0; for (len = 1; len < MAXBITS; len++) offs[len + 1] = offs[len] + count[len]; + /* sort symbols by length, by symbol order within each length */ for (sym = 0; sym < codes; sym++) if (lens[sym] != 0) work[offs[lens[sym]]++] = (unsigned short)sym; + /* Create and fill in decoding tables. In this loop, the table being filled is at next and has curr index bits. The code being used is huff @@ -139,26 +153,31 @@ unsigned short FAR *work; bits off of the bottom. For codes where len is less than drop + curr, those top drop + curr - len bits are incremented through all values to fill the table with replicated entries. + root is the number of index bits for the root table. When len exceeds root, sub-tables are created pointed to by the root entry with an index of the low root bits of huff. This is saved in low to check for when a new sub-table should be started. drop is zero when the root table is being filled, and drop is root when sub-tables are being filled. + When a new sub-table is needed, it is necessary to look ahead in the code lengths to determine what size sub-table is needed. The length counts are used for this, and so count[] is decremented as codes are entered in the tables. + used keeps track of how many table entries have been allocated from the provided *table space. It is checked when a LENS table is being made against the space in *table, ENOUGH, minus the maximum space needed by the worst case distance code, MAXD. This should never happen, but the sufficiency of ENOUGH has not been proven exhaustively, hence the check. This assumes that when type == LENS, bits == 9. + sym increments through all symbols, and the loop terminates when all codes of length max, i.e. all codes, have been processed. This routine permits incomplete codes, so another loop after this one fills in the rest of the decoding tables with invalid code markers. */ + /* set up for code type */ switch (type) { case CODES: @@ -177,6 +196,7 @@ unsigned short FAR *work; extra = dext; end = -1; } + /* initialize state for loop */ huff = 0; /* starting code */ sym = 0; /* starting code symbol */ @@ -187,9 +207,11 @@ unsigned short FAR *work; low = (unsigned)(-1); /* trigger new sub-table when len > root */ used = 1U << root; /* use root table entries */ mask = used - 1; /* mask for comparing low */ + /* check available table space */ if (type == LENS && used >= ENOUGH - MAXD) return 1; + /* process all codes and make table entries */ for (;;) { /* create table entry */ @@ -206,6 +228,7 @@ unsigned short FAR *work; this.op = (unsigned char)(32 + 64); /* end of block */ this.val = 0; } + /* replicate for those indices with low len bits equal to huff */ incr = 1U << (len - drop); fill = 1U << curr; @@ -214,6 +237,7 @@ unsigned short FAR *work; fill -= incr; next[(huff >> drop) + fill] = this; } while (fill != 0); + /* backwards increment the len-bit code huff */ incr = 1U << (len - 1); while (huff & incr) @@ -224,19 +248,23 @@ unsigned short FAR *work; } else huff = 0; + /* go to next symbol, update count, len */ sym++; if (--(count[len]) == 0) { if (len == max) break; len = lens[work[sym]]; } + /* create new sub-table if needed */ if (len > root && (huff & mask) != low) { /* if first time, transition to sub-tables */ if (drop == 0) drop = root; + /* increment past last table */ next += min; /* here min is 1 << curr */ + /* determine length of next table */ curr = len - drop; left = (int)(1 << curr); @@ -246,10 +274,12 @@ unsigned short FAR *work; curr++; left <<= 1; } + /* check for enough space */ used += 1U << curr; if (type == LENS && used >= ENOUGH - MAXD) return 1; + /* point entry in root table to sub-table */ low = huff & mask; (*table)[low].op = (unsigned char)curr; @@ -257,6 +287,7 @@ unsigned short FAR *work; (*table)[low].val = (unsigned short)(next - *table); } } + /* Fill in rest of table for incomplete codes. This loop is similar to the loop above in incrementing huff for table indices. It is assumed that @@ -275,8 +306,10 @@ unsigned short FAR *work; next = *table; this.bits = (unsigned char)len; } + /* put invalid code marker in table */ next[huff >> drop] = this; + /* backwards increment the len-bit code huff */ incr = 1U << (len - 1); while (huff & incr) @@ -288,6 +321,7 @@ unsigned short FAR *work; else huff = 0; } + /* set return parameters */ *table += used; *bits = root; |