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36ef0a677

Denys Vlasenko
Denys Vlasenko
2010-10-29
FAILED Duration: 276s

Subject

decompress_bunzip2: code shrink

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Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

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Commit Diff GitHub →

archival/libunarchive/decompress_bunzip2.c +67 -44
archival/libunarchive/decompress_bunzip2.c+67 -44
@@ -16,7 +16,7 @@
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
+ Note that about 2/3 of the time is spent in read_bunzip() reversing
the Burrows-Wheeler transformation. Much of that time is delay
resulting from cache misses.
@@ -70,23 +70,25 @@ struct bunzip_data {
/* I/O tracking data (file handles, buffers, positions, etc.) */
unsigned inbufBitCount, inbufBits;
int in_fd, out_fd, inbufCount, inbufPos /*, outbufPos*/;
- unsigned char *inbuf /*,*outbuf*/;
+ uint8_t *inbuf /*,*outbuf*/;
/* State for interrupting output loop */
- int writeCopies, writePos, writeRunCountdown, writeCount, writeCurrent;
+ int writeCopies, writePos, writeRunCountdown, writeCount;
+ int writeCurrent; /* actually a uint8_t */
/* The CRC values stored in the block header and calculated from the data */
uint32_t headerCRC, totalCRC, writeCRC;
/* Intermediate buffer and its size (in bytes) */
- unsigned *dbuf, dbufSize;
+ uint32_t *dbuf;
+ unsigned dbufSize;
/* For I/O error handling */
jmp_buf jmpbuf;
/* Big things go last (register-relative addressing can be larger for big offsets) */
uint32_t crc32Table[256];
- unsigned char selectors[32768]; /* nSelectors=15 bits */
+ uint8_t selectors[32768]; /* nSelectors=15 bits */
struct group_data groups[MAX_GROUPS]; /* Huffman coding tables */
};
/* typedef struct bunzip_data bunzip_data; -- done in .h file */
@@ -94,14 +96,15 @@ struct bunzip_data {
/* 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 get_bits(bunzip_data *bd, int bits_wanted)
{
unsigned bits = 0;
+ /* Cache bd->inbufBitCount in a CPU register (hopefully): */
+ int bit_count = bd->inbufBitCount;
/* 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 ((int)(bd->inbufBitCount) < bits_wanted) {
+ while (bit_count < bits_wanted) {
/* If we need to read more data from file into byte buffer, do so */
if (bd->inbufPos == bd->inbufCount) {
@@ -113,33 +116,35 @@ static unsigned get_bits(bunzip_data *bd, int bits_wanted)
}
/* Avoid 32-bit overflow (dump bit buffer to top of output) */
- if (bd->inbufBitCount >= 24) {
- bits = bd->inbufBits & ((1 << bd->inbufBitCount) - 1);
- bits_wanted -= bd->inbufBitCount;
+ if (bit_count >= 24) {
+ bits = bd->inbufBits & ((1 << bit_count) - 1);
+ bits_wanted -= bit_count;
bits <<= bits_wanted;
- bd->inbufBitCount = 0;
+ bit_count = 0;
}
/* Grab next 8 bits of input from buffer. */
bd->inbufBits = (bd->inbufBits << 8) | bd->inbuf[bd->inbufPos++];
- bd->inbufBitCount += 8;
+ bit_count += 8;
}
/* Calculate result */
- bd->inbufBitCount -= bits_wanted;
- bits |= (bd->inbufBits >> bd->inbufBitCount) & ((1 << bits_wanted) - 1);
+ bit_count -= bits_wanted;
+ bd->inbufBitCount = bit_count;
+ bits |= (bd->inbufBits >> bit_count) & ((1 << bits_wanted) - 1);
return bits;
}
-/* Unpacks the next block and sets up for the inverse burrows-wheeler step. */
+/* Unpacks the next block and sets up for the inverse Burrows-Wheeler step. */
static int get_next_block(bunzip_data *bd)
{
struct group_data *hufGroup;
int dbufCount, nextSym, dbufSize, groupCount, *base, *limit, selector,
i, j, k, t, runPos, symCount, symTotal, nSelectors, byteCount[256];
- unsigned char uc, symToByte[256], mtfSymbol[256], *selectors;
- unsigned *dbuf, origPtr;
+ uint8_t uc, symToByte[256], mtfSymbol[256], *selectors;
+ uint32_t *dbuf;
+ unsigned origPtr;
dbuf = bd->dbuf;
dbufSize = bd->dbufSize;
@@ -200,7 +205,8 @@ static int get_next_block(bunzip_data *bd)
/* Decode MTF to get the next selector */
uc = mtfSymbol[j];
- for (;j;j--) mtfSymbol[j] = mtfSymbol[j-1];
+ for (; j; j--)
+ mtfSymbol[j] = mtfSymbol[j-1];
mtfSymbol[0] = selectors[i] = uc;
}
@@ -208,7 +214,7 @@ static int get_next_block(bunzip_data *bd)
literal symbols, plus two run symbols (RUNA, RUNB) */
symCount = symTotal + 2;
for (j = 0; j < groupCount; j++) {
- unsigned char length[MAX_SYMBOLS];
+ uint8_t length[MAX_SYMBOLS];
/* 8 bits is ALMOST enough for temp[], see below */
unsigned temp[MAX_HUFCODE_BITS+1];
int minLen, maxLen, pp;
@@ -315,7 +321,7 @@ static int get_next_block(bunzip_data *bd)
memset(byteCount, 0, sizeof(byteCount)); /* smaller, maybe slower? */
for (i = 0; i < 256; i++) {
//byteCount[i] = 0;
- mtfSymbol[i] = (unsigned char)i;
+ mtfSymbol[i] = (uint8_t)i;
}
/* Loop through compressed symbols. */
@@ -456,7 +462,7 @@ static int get_next_block(bunzip_data *bd)
/* Figure out what order dbuf would be in if we sorted it. */
for (i = 0; i < dbufCount; i++) {
- uc = (unsigned char)(dbuf[i] & 0xff);
+ uc = (uint8_t)dbuf[i];
dbuf[byteCount[uc]] |= (i << 8);
byteCount[uc]++;
}
@@ -465,10 +471,11 @@ static int get_next_block(bunzip_data *bd)
doesn't get output, and if the first three characters are identical
it doesn't qualify as a run (hence writeRunCountdown=5). */
if (dbufCount) {
+ uint32_t tmp;
if ((int)origPtr >= dbufCount) return RETVAL_DATA_ERROR;
- bd->writePos = dbuf[origPtr];
- bd->writeCurrent = (unsigned char)(bd->writePos & 0xff);
- bd->writePos >>= 8;
+ tmp = dbuf[origPtr];
+ bd->writeCurrent = (uint8_t)tmp;
+ bd->writePos = (tmp >> 8);
bd->writeRunCountdown = 5;
}
bd->writeCount = dbufCount;
@@ -476,7 +483,7 @@ static int get_next_block(bunzip_data *bd)
return RETVAL_OK;
}
-/* Undo burrows-wheeler transform on intermediate buffer to produce output.
+/* Undo Burrows-Wheeler transform on intermediate buffer to produce output.
If start_bunzip was initialized with out_fd=-1, then up to len bytes of
data are written to outbuf. Return value is number of bytes written or
error (all errors are negative numbers). If out_fd!=-1, outbuf and len
@@ -484,7 +491,7 @@ static int get_next_block(bunzip_data *bd)
*/
int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
{
- const unsigned *dbuf;
+ const uint32_t *dbuf;
int pos, current, previous, gotcount;
/* If last read was short due to end of file, return last block now */
@@ -500,6 +507,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
Huffman-decoded a block into the intermediate buffer yet). */
if (bd->writeCopies) {
+ dec_writeCopies:
/* Inside the loop, writeCopies means extra copies (beyond 1) */
--bd->writeCopies;
@@ -508,10 +516,10 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
/* If the output buffer is full, snapshot state and return */
if (gotcount >= len) {
- bd->writePos = pos;
- bd->writeCurrent = current;
- bd->writeCopies++;
- return len;
+ /* Unlikely branch.
+ * Use of "goto" instead of keeping code here
+ * helps compiler to realize this. */
+ goto outbuf_full;
}
/* Write next byte into output buffer, updating CRC */
@@ -521,15 +529,21 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
/* Loop now if we're outputting multiple copies of this byte */
if (bd->writeCopies) {
- --bd->writeCopies;
- continue;
+ /* Unlikely branch */
+ /*--bd->writeCopies;*/
+ /*continue;*/
+ /* Same, but (ab)using other existing --writeCopies operation.
+ * Luckily, this also compiles into just one branch insn: */
+ goto dec_writeCopies;
}
decode_next_byte:
- if (!bd->writeCount--) break;
+ if (--bd->writeCount < 0)
+ break; /* input block is fully consumed, need next one */
+
/* Follow sequence vector to undo Burrows-Wheeler transform */
previous = current;
pos = dbuf[pos];
- current = pos & 0xff;
+ current = (uint8_t)pos;
pos >>= 8;
/* After 3 consecutive copies of the same byte, the 4th
@@ -539,7 +553,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
if (current != previous)
bd->writeRunCountdown = 4;
} else {
-
+ /* Unlikely branch */
/* We have a repeated run, this byte indicates the count */
bd->writeCopies = current;
current = previous;
@@ -551,9 +565,9 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
/* Subtract the 1 copy we'd output anyway to get extras */
--bd->writeCopies;
}
- }
+ } /* for(;;) */
- /* Decompression of this block completed successfully */
+ /* Decompression of this input block completed successfully */
bd->writeCRC = ~bd->writeCRC;
bd->totalCRC = ((bd->totalCRC << 1) | (bd->totalCRC >> 31)) ^ bd->writeCRC;
@@ -565,16 +579,25 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
}
/* Refill the intermediate buffer by Huffman-decoding next block of input */
- /* (previous is just a convenient unused temp variable here) */
- previous = get_next_block(bd);
- if (previous) {
- bd->writeCount = previous;
- return (previous != RETVAL_LAST_BLOCK) ? previous : gotcount;
+ {
+ int r = get_next_block(bd);
+ if (r) {
+ bd->writeCount = r;
+ return (r != RETVAL_LAST_BLOCK) ? r : gotcount;
+ }
}
+
bd->writeCRC = ~0;
pos = bd->writePos;
current = bd->writeCurrent;
goto decode_next_byte;
+
+ outbuf_full:
+ /* Output buffer is full, snapshot state and return */
+ bd->writePos = pos;
+ bd->writeCurrent = current;
+ bd->writeCopies++;
+ return gotcount;
}
/* Allocate the structure, read file header. If in_fd==-1, inbuf must contain
@@ -607,7 +630,7 @@ int FAST_FUNC start_bunzip(bunzip_data **bdp, int in_fd,
/* in this case, bd->inbuf is read-only */
bd->inbuf = (void*)inbuf; /* cast away const-ness */
} else {
- bd->inbuf = (unsigned char *)(bd + 1);
+ bd->inbuf = (uint8_t*)(bd + 1);
memcpy(bd->inbuf, inbuf, len);
}
bd->inbufCount = len;
@@ -634,7 +657,7 @@ int FAST_FUNC start_bunzip(bunzip_data **bdp, int in_fd,
bd->dbufSize = 100000 * (i - h0);
/* Cannot use xmalloc - may leak bd in NOFORK case! */
- bd->dbuf = malloc_or_warn(bd->dbufSize * sizeof(int));
+ bd->dbuf = malloc_or_warn(bd->dbufSize * sizeof(bd->dbuf[0]));
if (!bd->dbuf) {
free(bd);
xfunc_die();