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gzip cleanup part #10

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This commit is contained in:
Denis Vlasenko 2007-01-07 19:40:50 +00:00
parent 89af56b3e5
commit 56c83eaaf5
1 changed files with 344 additions and 356 deletions
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700
archival/gzip.c
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@ -201,7 +201,8 @@ typedef unsigned IPos;
array = xzalloc((size_t)(((size)+1L)/2) * 2*sizeof(type)); \
}
#define FREE(array) { \
#define FREE(array) \
{ \
free(array); \
array = NULL; \
}
@ -272,21 +273,6 @@ enum {
};
/* ===========================================================================
*/
static void fill_window(void);
static int longest_match(IPos cur_match);
#ifdef DEBUG
static void check_match(IPos start, IPos match, int length);
#endif
/* from trees.c */
static int ct_tally(int dist, int lc);
static ulg flush_block(char *buf, ulg stored_len, int eof);
/* global buffers */
/* To save memory for 16 bit systems, some arrays are overlaid between
@ -585,6 +571,65 @@ static void copy_block(char *buf, unsigned len, int header)
}
/* ===========================================================================
* Fill the window when the lookahead becomes insufficient.
* Updates strstart and lookahead, and sets eofile if end of input file.
* IN assertion: lookahead < MIN_LOOKAHEAD && strstart + lookahead > 0
* OUT assertions: at least one byte has been read, or eofile is set;
* file reads are performed for at least two bytes (required for the
* translate_eol option).
*/
static void fill_window(void)
{
unsigned n, m;
unsigned more = WINDOW_SIZE - lookahead - strstart;
/* Amount of free space at the end of the window. */
/* If the window is almost full and there is insufficient lookahead,
* move the upper half to the lower one to make room in the upper half.
*/
if (more == (unsigned) -1) {
/* Very unlikely, but possible on 16 bit machine if strstart == 0
* and lookahead == 1 (input done one byte at time)
*/
more--;
} else if (strstart >= WSIZE + MAX_DIST) {
/* By the IN assertion, the window is not empty so we can't confuse
* more == 0 with more == 64K on a 16 bit machine.
*/
Assert(WINDOW_SIZE == 2 * WSIZE, "no sliding with BIG_MEM");
memcpy(window, window + WSIZE, WSIZE);
match_start -= WSIZE;
strstart -= WSIZE; /* we now have strstart >= MAX_DIST: */
block_start -= WSIZE;
for (n = 0; n < HASH_SIZE; n++) {
m = head[n];
head[n] = (Pos) (m >= WSIZE ? m - WSIZE : 0);
}
for (n = 0; n < WSIZE; n++) {
m = prev[n];
prev[n] = (Pos) (m >= WSIZE ? m - WSIZE : 0);
/* If n is not on any hash chain, prev[n] is garbage but
* its value will never be used.
*/
}
more += WSIZE;
}
/* At this point, more >= 2 */
if (!eofile) {
n = file_read(window + strstart + lookahead, more);
if (n == 0 || n == (unsigned) -1) {
eofile = 1;
} else {
lookahead += n;
}
}
}
/* ===========================================================================
* Update a hash value with the given input byte
* IN assertion: all calls to to UPDATE_HASH are made with consecutive
@ -746,202 +791,6 @@ static void check_match(IPos start, IPos match, int length)
#endif
/* ===========================================================================
* Fill the window when the lookahead becomes insufficient.
* Updates strstart and lookahead, and sets eofile if end of input file.
* IN assertion: lookahead < MIN_LOOKAHEAD && strstart + lookahead > 0
* OUT assertions: at least one byte has been read, or eofile is set;
* file reads are performed for at least two bytes (required for the
* translate_eol option).
*/
static void fill_window(void)
{
unsigned n, m;
unsigned more = WINDOW_SIZE - lookahead - strstart;
/* Amount of free space at the end of the window. */
/* If the window is almost full and there is insufficient lookahead,
* move the upper half to the lower one to make room in the upper half.
*/
if (more == (unsigned) -1) {
/* Very unlikely, but possible on 16 bit machine if strstart == 0
* and lookahead == 1 (input done one byte at time)
*/
more--;
} else if (strstart >= WSIZE + MAX_DIST) {
/* By the IN assertion, the window is not empty so we can't confuse
* more == 0 with more == 64K on a 16 bit machine.
*/
Assert(WINDOW_SIZE == 2 * WSIZE, "no sliding with BIG_MEM");
memcpy(window, window + WSIZE, WSIZE);
match_start -= WSIZE;
strstart -= WSIZE; /* we now have strstart >= MAX_DIST: */
block_start -= WSIZE;
for (n = 0; n < HASH_SIZE; n++) {
m = head[n];
head[n] = (Pos) (m >= WSIZE ? m - WSIZE : 0);
}
for (n = 0; n < WSIZE; n++) {
m = prev[n];
prev[n] = (Pos) (m >= WSIZE ? m - WSIZE : 0);
/* If n is not on any hash chain, prev[n] is garbage but
* its value will never be used.
*/
}
more += WSIZE;
}
/* At this point, more >= 2 */
if (!eofile) {
n = file_read(window + strstart + lookahead, more);
if (n == 0 || n == (unsigned) -1) {
eofile = 1;
} else {
lookahead += n;
}
}
}
/* ===========================================================================
* Same as above, but achieves better compression. We use a lazy
* evaluation for matches: a match is finally adopted only if there is
* no better match at the next window position.
*
* Processes a new input file and return its compressed length. Sets
* the compressed length, crc, deflate flags and internal file
* attributes.
*/
/* Flush the current block, with given end-of-file flag.
* IN assertion: strstart is set to the end of the current match. */
#define FLUSH_BLOCK(eof) \
flush_block( \
block_start >= 0L \
? (char*)&window[(unsigned)block_start] \
: (char*)NULL, \
(long)strstart - block_start, \
(eof) \
)
/* Insert string s in the dictionary and set match_head to the previous head
* of the hash chain (the most recent string with same hash key). Return
* the previous length of the hash chain.
* IN assertion: all calls to to INSERT_STRING are made with consecutive
* input characters and the first MIN_MATCH bytes of s are valid
* (except for the last MIN_MATCH-1 bytes of the input file). */
#define INSERT_STRING(s, match_head) \
{ \
UPDATE_HASH(ins_h, window[(s) + MIN_MATCH-1]); \
prev[(s) & WMASK] = match_head = head[ins_h]; \
head[ins_h] = (s); \
}
static ulg deflate(void)
{
IPos hash_head; /* head of hash chain */
IPos prev_match; /* previous match */
int flush; /* set if current block must be flushed */
int match_available = 0; /* set if previous match exists */
unsigned match_length = MIN_MATCH - 1; /* length of best match */
/* Process the input block. */
while (lookahead != 0) {
/* Insert the string window[strstart .. strstart+2] in the
* dictionary, and set hash_head to the head of the hash chain:
*/
INSERT_STRING(strstart, hash_head);
/* Find the longest match, discarding those <= prev_length.
*/
prev_length = match_length, prev_match = match_start;
match_length = MIN_MATCH - 1;
if (hash_head != 0 && prev_length < max_lazy_match
&& strstart - hash_head <= MAX_DIST
) {
/* To simplify the code, we prevent matches with the string
* of window index 0 (in particular we have to avoid a match
* of the string with itself at the start of the input file).
*/
match_length = longest_match(hash_head);
/* longest_match() sets match_start */
if (match_length > lookahead)
match_length = lookahead;
/* Ignore a length 3 match if it is too distant: */
if (match_length == MIN_MATCH && strstart - match_start > TOO_FAR) {
/* If prev_match is also MIN_MATCH, match_start is garbage
* but we will ignore the current match anyway.
*/
match_length--;
}
}
/* If there was a match at the previous step and the current
* match is not better, output the previous match:
*/
if (prev_length >= MIN_MATCH && match_length <= prev_length) {
check_match(strstart - 1, prev_match, prev_length);
flush = ct_tally(strstart - 1 - prev_match, prev_length - MIN_MATCH);
/* Insert in hash table all strings up to the end of the match.
* strstart-1 and strstart are already inserted.
*/
lookahead -= prev_length - 1;
prev_length -= 2;
do {
strstart++;
INSERT_STRING(strstart, hash_head);
/* strstart never exceeds WSIZE-MAX_MATCH, so there are
* always MIN_MATCH bytes ahead. If lookahead < MIN_MATCH
* these bytes are garbage, but it does not matter since the
* next lookahead bytes will always be emitted as literals.
*/
} while (--prev_length != 0);
match_available = 0;
match_length = MIN_MATCH - 1;
strstart++;
if (flush) {
FLUSH_BLOCK(0);
block_start = strstart;
}
} else if (match_available) {
/* If there was no match at the previous position, output a
* single literal. If there was a match but the current match
* is longer, truncate the previous match to a single literal.
*/
Tracevv((stderr, "%c", window[strstart - 1]));
if (ct_tally(0, window[strstart - 1])) {
FLUSH_BLOCK(0);
block_start = strstart;
}
strstart++;
lookahead--;
} else {
/* There is no previous match to compare with, wait for
* the next step to decide.
*/
match_available = 1;
strstart++;
lookahead--;
}
Assert(strstart <= isize && lookahead <= isize, "a bit too far");
/* Make sure that we always have enough lookahead, except
* at the end of the input file. We need MAX_MATCH bytes
* for the next match, plus MIN_MATCH bytes to insert the
* string following the next match.
*/
while (lookahead < MIN_LOOKAHEAD && !eofile)
fill_window();
}
if (match_available)
ct_tally(0, window[strstart - 1]);
return FLUSH_BLOCK(1); /* eof */
}
/* trees.c -- output deflated data using Huffman coding
* Copyright (C) 1992-1993 Jean-loup Gailly
* This is free software; you can redistribute it and/or modify it under the
@ -991,10 +840,6 @@ static ulg deflate(void)
* file. Returns the total compressed length for the file so far.
*/
/* ===========================================================================
* Constants
*/
#define MAX_BITS 15
/* All codes must not exceed MAX_BITS bits */
@ -1087,9 +932,7 @@ static const extra_bits_t extra_blbits[BL_CODES] = {
/* repeat a zero length 11-138 times (7 bits of repeat count) */
/* ===========================================================================
* Local data
*/
*/
/* Data structure describing a single value and its code string. */
typedef struct ct_data {
union {
@ -1231,8 +1074,6 @@ static int *file_method; /* pointer to DEFLATE or STORE */
/* ===========================================================================
*/
static void init_block(void);
static void gen_bitlen(tree_desc * desc);
static void gen_codes(ct_data * tree, int max_code);
static void build_tree(tree_desc * desc);
static void scan_tree(ct_data * tree, int max_code);
@ -1240,7 +1081,6 @@ static void send_tree(ct_data * tree, int max_code);
static int build_bl_tree(void);
static void send_all_trees(int lcodes, int dcodes, int blcodes);
static void compress_block(ct_data * ltree, ct_data * dtree);
static void set_file_type(void);
#ifndef DEBUG
@ -1259,9 +1099,31 @@ static void set_file_type(void);
/* Mapping from a distance to a distance code. dist is the distance - 1 and
* must not have side effects. dist_code[256] and dist_code[257] are never
* used.
* The arguments must not have side effects.
*/
/* the arguments must not have side effects */
/* ===========================================================================
* Initialize a new block.
*/
static void init_block(void)
{
int n; /* iterates over tree elements */
/* Initialize the trees. */
for (n = 0; n < L_CODES; n++)
dyn_ltree[n].Freq = 0;
for (n = 0; n < D_CODES; n++)
dyn_dtree[n].Freq = 0;
for (n = 0; n < BL_CODES; n++)
bl_tree[n].Freq = 0;
dyn_ltree[END_BLOCK].Freq = 1;
opt_len = static_len = 0L;
last_lit = last_dist = last_flags = 0;
flags = 0;
flag_bit = 1;
}
/* ===========================================================================
@ -1289,7 +1151,7 @@ static void ct_init(ush * attr, int *methodp)
for (code = 0; code < LENGTH_CODES - 1; code++) {
base_length[code] = length;
for (n = 0; n < (1 << extra_lbits[code]); n++) {
length_code[length++] = (uch) code;
length_code[length++] = code;
}
}
Assert(length == 256, "ct_init: length != 256");
@ -1297,7 +1159,7 @@ static void ct_init(ush * attr, int *methodp)
* in two different ways: code 284 + 5 bits or code 285, so we
* overwrite length_code[255] to use the best encoding:
*/
length_code[length - 1] = (uch) code;
length_code[length - 1] = code;
/* Initialize the mapping dist (0..32K) -> dist code (0..29) */
dist = 0;
@ -1355,29 +1217,6 @@ static void ct_init(ush * attr, int *methodp)
}
/* ===========================================================================
* Initialize a new block.
*/
static void init_block(void)
{
int n; /* iterates over tree elements */
/* Initialize the trees. */
for (n = 0; n < L_CODES; n++)
dyn_ltree[n].Freq = 0;
for (n = 0; n < D_CODES; n++)
dyn_dtree[n].Freq = 0;
for (n = 0; n < BL_CODES; n++)
bl_tree[n].Freq = 0;
dyn_ltree[END_BLOCK].Freq = 1;
opt_len = static_len = 0L;
last_lit = last_dist = last_flags = 0;
flags = 0;
flag_bit = 1;
}
/* ===========================================================================
* Restore the heap property by moving down the tree starting at node k,
* exchanging a node with the smallest of its two sons if necessary, stopping
@ -1470,7 +1309,7 @@ static void gen_bitlen(tree_desc * desc)
opt_len += (ulg) f *(bits + xbits);
if (stree)
static_len += (ulg) f *(stree[n].Len + xbits);
static_len += (ulg) f * (stree[n].Len + xbits);
}
if (overflow == 0)
return;
@ -1513,6 +1352,7 @@ static void gen_bitlen(tree_desc * desc)
}
}
/* ===========================================================================
* Generate the codes for a given tree and bit counts (which need not be
* optimal).
@ -1556,6 +1396,7 @@ static void gen_codes(ct_data * tree, int max_code)
}
}
/* ===========================================================================
* Construct one Huffman tree and assigns the code bit strings and lengths.
* Update the total bit length for the current block.
@ -1662,6 +1503,7 @@ static void build_tree(tree_desc * desc)
gen_codes((ct_data *) tree, max_code);
}
/* ===========================================================================
* Scan a literal or distance tree to determine the frequencies of the codes
* in the bit length tree. Updates opt_len to take into account the repeat
@ -1715,6 +1557,7 @@ static void scan_tree(ct_data * tree, int max_code)
}
}
/* ===========================================================================
* Send a literal or distance tree in compressed form, using the codes in
* bl_tree.
@ -1772,6 +1615,7 @@ static void send_tree(ct_data * tree, int max_code)
}
}
/* ===========================================================================
* Construct the Huffman tree for the bit lengths and return the index in
* bl_order of the last bit length code to send.
@ -1805,6 +1649,7 @@ static int build_bl_tree(void)
return max_blindex;
}
/* ===========================================================================
* Send the header for a block using dynamic Huffman trees: the counts, the
* lengths of the bit length codes, the literal tree and the distance tree.
@ -1834,100 +1679,32 @@ static void send_all_trees(int lcodes, int dcodes, int blcodes)
Tracev((stderr, "\ndist tree: sent %ld", bits_sent));
}
/* ===========================================================================
* Determine the best encoding for the current block: dynamic trees, static
* trees or store, and output the encoded block to the zip file. This function
* returns the total compressed length for the file so far.
* Set the file type to ASCII or BINARY, using a crude approximation:
* binary if more than 20% of the bytes are <= 6 or >= 128, ascii otherwise.
* IN assertion: the fields freq of dyn_ltree are set and the total of all
* frequencies does not exceed 64K (to fit in an int on 16 bit machines).
*/
static ulg flush_block(char *buf, ulg stored_len, int eof)
static void set_file_type(void)
{
ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
int max_blindex; /* index of last bit length code of non zero freq */
int n = 0;
unsigned ascii_freq = 0;
unsigned bin_freq = 0;
flag_buf[last_flags] = flags; /* Save the flags for the last 8 items */
/* Check if the file is ascii or binary */
if (*file_type == (ush) UNKNOWN)
set_file_type();
/* Construct the literal and distance trees */
build_tree((tree_desc *) (&l_desc));
Tracev((stderr, "\nlit data: dyn %ld, stat %ld", opt_len, static_len));
build_tree((tree_desc *) (&d_desc));
Tracev((stderr, "\ndist data: dyn %ld, stat %ld", opt_len, static_len));
/* At this point, opt_len and static_len are the total bit lengths of
* the compressed block data, excluding the tree representations.
*/
/* Build the bit length tree for the above two trees, and get the index
* in bl_order of the last bit length code to send.
*/
max_blindex = build_bl_tree();
/* Determine the best encoding. Compute first the block length in bytes */
opt_lenb = (opt_len + 3 + 7) >> 3;
static_lenb = (static_len + 3 + 7) >> 3;
Trace((stderr,
"\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u dist %u ",
opt_lenb, opt_len, static_lenb, static_len, stored_len,
last_lit, last_dist));
if (static_lenb <= opt_lenb)
opt_lenb = static_lenb;
/* If compression failed and this is the first and last block,
* and if the zip file can be seeked (to rewrite the local header),
* the whole file is transformed into a stored file:
*/
if (stored_len <= opt_lenb && eof && compressed_len == 0L && seekable()) {
/* Since LIT_BUFSIZE <= 2*WSIZE, the input data must be there: */
if (buf == NULL)
bb_error_msg("block vanished");
copy_block(buf, (unsigned) stored_len, 0); /* without header */
compressed_len = stored_len << 3;
*file_method = STORED;
} else if (stored_len + 4 <= opt_lenb && buf != (char *) 0) {
/* 4: two words for the lengths */
/* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
* Otherwise we can't have processed more than WSIZE input bytes since
* the last block flush, because compression would have been
* successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
* transform a block into a stored block.
*/
send_bits((STORED_BLOCK << 1) + eof, 3); /* send block type */
compressed_len = (compressed_len + 3 + 7) & ~7L;
compressed_len += (stored_len + 4) << 3;
copy_block(buf, (unsigned) stored_len, 1); /* with header */
} else if (static_lenb == opt_lenb) {
send_bits((STATIC_TREES << 1) + eof, 3);
compress_block((ct_data *) static_ltree, (ct_data *) static_dtree);
compressed_len += 3 + static_len;
} else {
send_bits((DYN_TREES << 1) + eof, 3);
send_all_trees(l_desc.max_code + 1, d_desc.max_code + 1,
max_blindex + 1);
compress_block((ct_data *) dyn_ltree, (ct_data *) dyn_dtree);
compressed_len += 3 + opt_len;
while (n < 7)
bin_freq += dyn_ltree[n++].Freq;
while (n < 128)
ascii_freq += dyn_ltree[n++].Freq;
while (n < LITERALS)
bin_freq += dyn_ltree[n++].Freq;
*file_type = (bin_freq > (ascii_freq >> 2)) ? BINARY : ASCII;
if (*file_type == BINARY && translate_eol) {
bb_error_msg("-l used on binary file");
}
Assert(compressed_len == bits_sent, "bad compressed size");
init_block();
if (eof) {
bi_windup();
compressed_len += 7; /* align on byte boundary */
}
Tracev((stderr, "\ncomprlen %lu(%lu) ", compressed_len >> 3,
compressed_len - 7 * eof));
return compressed_len >> 3;
}
/* ===========================================================================
* Save the match info and tally the frequency counts. Return true if
* the current block must be flushed.
@ -2034,30 +1811,241 @@ static void compress_block(ct_data * ltree, ct_data * dtree)
SEND_CODE(END_BLOCK, ltree);
}
/* ===========================================================================
* Set the file type to ASCII or BINARY, using a crude approximation:
* binary if more than 20% of the bytes are <= 6 or >= 128, ascii otherwise.
* IN assertion: the fields freq of dyn_ltree are set and the total of all
* frequencies does not exceed 64K (to fit in an int on 16 bit machines).
*/
static void set_file_type(void)
{
int n = 0;
unsigned ascii_freq = 0;
unsigned bin_freq = 0;
while (n < 7)
bin_freq += dyn_ltree[n++].Freq;
while (n < 128)
ascii_freq += dyn_ltree[n++].Freq;
while (n < LITERALS)
bin_freq += dyn_ltree[n++].Freq;
*file_type = (bin_freq > (ascii_freq >> 2)) ? BINARY : ASCII;
if (*file_type == BINARY && translate_eol) {
bb_error_msg("-l used on binary file");
/* ===========================================================================
* Determine the best encoding for the current block: dynamic trees, static
* trees or store, and output the encoded block to the zip file. This function
* returns the total compressed length for the file so far.
*/
static ulg flush_block(char *buf, ulg stored_len, int eof)
{
ulg opt_lenb, static_lenb; /* opt_len and static_len in bytes */
int max_blindex; /* index of last bit length code of non zero freq */
flag_buf[last_flags] = flags; /* Save the flags for the last 8 items */
/* Check if the file is ascii or binary */
if (*file_type == (ush) UNKNOWN)
set_file_type();
/* Construct the literal and distance trees */
build_tree((tree_desc *) (&l_desc));
Tracev((stderr, "\nlit data: dyn %ld, stat %ld", opt_len, static_len));
build_tree((tree_desc *) (&d_desc));
Tracev((stderr, "\ndist data: dyn %ld, stat %ld", opt_len, static_len));
/* At this point, opt_len and static_len are the total bit lengths of
* the compressed block data, excluding the tree representations.
*/
/* Build the bit length tree for the above two trees, and get the index
* in bl_order of the last bit length code to send.
*/
max_blindex = build_bl_tree();
/* Determine the best encoding. Compute first the block length in bytes */
opt_lenb = (opt_len + 3 + 7) >> 3;
static_lenb = (static_len + 3 + 7) >> 3;
Trace((stderr,
"\nopt %lu(%lu) stat %lu(%lu) stored %lu lit %u dist %u ",
opt_lenb, opt_len, static_lenb, static_len, stored_len,
last_lit, last_dist));
if (static_lenb <= opt_lenb)
opt_lenb = static_lenb;
/* If compression failed and this is the first and last block,
* and if the zip file can be seeked (to rewrite the local header),
* the whole file is transformed into a stored file:
*/
if (stored_len <= opt_lenb && eof && compressed_len == 0L && seekable()) {
/* Since LIT_BUFSIZE <= 2*WSIZE, the input data must be there: */
if (buf == NULL)
bb_error_msg("block vanished");
copy_block(buf, (unsigned) stored_len, 0); /* without header */
compressed_len = stored_len << 3;
*file_method = STORED;
} else if (stored_len + 4 <= opt_lenb && buf != (char *) 0) {
/* 4: two words for the lengths */
/* The test buf != NULL is only necessary if LIT_BUFSIZE > WSIZE.
* Otherwise we can't have processed more than WSIZE input bytes since
* the last block flush, because compression would have been
* successful. If LIT_BUFSIZE <= WSIZE, it is never too late to
* transform a block into a stored block.
*/
send_bits((STORED_BLOCK << 1) + eof, 3); /* send block type */
compressed_len = (compressed_len + 3 + 7) & ~7L;
compressed_len += (stored_len + 4) << 3;
copy_block(buf, (unsigned) stored_len, 1); /* with header */
} else if (static_lenb == opt_lenb) {
send_bits((STATIC_TREES << 1) + eof, 3);
compress_block((ct_data *) static_ltree, (ct_data *) static_dtree);
compressed_len += 3 + static_len;
} else {
send_bits((DYN_TREES << 1) + eof, 3);
send_all_trees(l_desc.max_code + 1, d_desc.max_code + 1,
max_blindex + 1);
compress_block((ct_data *) dyn_ltree, (ct_data *) dyn_dtree);
compressed_len += 3 + opt_len;
}
Assert(compressed_len == bits_sent, "bad compressed size");
init_block();
if (eof) {
bi_windup();
compressed_len += 7; /* align on byte boundary */
}
Tracev((stderr, "\ncomprlen %lu(%lu) ", compressed_len >> 3,
compressed_len - 7 * eof));
return compressed_len >> 3;
}
/* ===========================================================================
* Same as above, but achieves better compression. We use a lazy
* evaluation for matches: a match is finally adopted only if there is
* no better match at the next window position.
*
* Processes a new input file and return its compressed length. Sets
* the compressed length, crc, deflate flags and internal file
* attributes.
*/
/* Flush the current block, with given end-of-file flag.
* IN assertion: strstart is set to the end of the current match. */
#define FLUSH_BLOCK(eof) \
flush_block( \
block_start >= 0L \
? (char*)&window[(unsigned)block_start] \
: (char*)NULL, \
(long)strstart - block_start, \
(eof) \
)
/* Insert string s in the dictionary and set match_head to the previous head
* of the hash chain (the most recent string with same hash key). Return
* the previous length of the hash chain.
* IN assertion: all calls to to INSERT_STRING are made with consecutive
* input characters and the first MIN_MATCH bytes of s are valid
* (except for the last MIN_MATCH-1 bytes of the input file). */
#define INSERT_STRING(s, match_head) \
{ \
UPDATE_HASH(ins_h, window[(s) + MIN_MATCH-1]); \
prev[(s) & WMASK] = match_head = head[ins_h]; \
head[ins_h] = (s); \
}
static ulg deflate(void)
{
IPos hash_head; /* head of hash chain */
IPos prev_match; /* previous match */
int flush; /* set if current block must be flushed */
int match_available = 0; /* set if previous match exists */
unsigned match_length = MIN_MATCH - 1; /* length of best match */
/* Process the input block. */
while (lookahead != 0) {
/* Insert the string window[strstart .. strstart+2] in the
* dictionary, and set hash_head to the head of the hash chain:
*/
INSERT_STRING(strstart, hash_head);
/* Find the longest match, discarding those <= prev_length.
*/
prev_length = match_length, prev_match = match_start;
match_length = MIN_MATCH - 1;
if (hash_head != 0 && prev_length < max_lazy_match
&& strstart - hash_head <= MAX_DIST
) {
/* To simplify the code, we prevent matches with the string
* of window index 0 (in particular we have to avoid a match
* of the string with itself at the start of the input file).
*/
match_length = longest_match(hash_head);
/* longest_match() sets match_start */
if (match_length > lookahead)
match_length = lookahead;
/* Ignore a length 3 match if it is too distant: */
if (match_length == MIN_MATCH && strstart - match_start > TOO_FAR) {
/* If prev_match is also MIN_MATCH, match_start is garbage
* but we will ignore the current match anyway.
*/
match_length--;
}
}
/* If there was a match at the previous step and the current
* match is not better, output the previous match:
*/
if (prev_length >= MIN_MATCH && match_length <= prev_length) {
check_match(strstart - 1, prev_match, prev_length);
flush = ct_tally(strstart - 1 - prev_match, prev_length - MIN_MATCH);
/* Insert in hash table all strings up to the end of the match.
* strstart-1 and strstart are already inserted.
*/
lookahead -= prev_length - 1;
prev_length -= 2;
do {
strstart++;
INSERT_STRING(strstart, hash_head);
/* strstart never exceeds WSIZE-MAX_MATCH, so there are
* always MIN_MATCH bytes ahead. If lookahead < MIN_MATCH
* these bytes are garbage, but it does not matter since the
* next lookahead bytes will always be emitted as literals.
*/
} while (--prev_length != 0);
match_available = 0;
match_length = MIN_MATCH - 1;
strstart++;
if (flush) {
FLUSH_BLOCK(0);
block_start = strstart;
}
} else if (match_available) {
/* If there was no match at the previous position, output a
* single literal. If there was a match but the current match
* is longer, truncate the previous match to a single literal.
*/
Tracevv((stderr, "%c", window[strstart - 1]));
if (ct_tally(0, window[strstart - 1])) {
FLUSH_BLOCK(0);
block_start = strstart;
}
strstart++;
lookahead--;
} else {
/* There is no previous match to compare with, wait for
* the next step to decide.
*/
match_available = 1;
strstart++;
lookahead--;
}
Assert(strstart <= isize && lookahead <= isize, "a bit too far");
/* Make sure that we always have enough lookahead, except
* at the end of the input file. We need MAX_MATCH bytes
* for the next match, plus MIN_MATCH bytes to insert the
* string following the next match.
*/
while (lookahead < MIN_LOOKAHEAD && !eofile)
fill_window();
}
if (match_available)
ct_tally(0, window[strstart - 1]);
return FLUSH_BLOCK(1); /* eof */
}
/* ===========================================================================
* Deflate in to out.
* IN assertions: the input and output buffers are cleared.