emo/busybox
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

decompress_bunzip2: keep bd->writeCRC in CPU reg in the hot loop

Browse Source 
-5 bytes on 64-bit, +7 bytes on 32-bit.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
This commit is contained in:
Denys Vlasenko 2010-10-29 18:16:29 +02:00
parent f29a1c5656
commit bf3bec51fc
1 changed files with 28 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
archival/libunarchive/decompress_bunzip2.c
View File

@ -492,15 +492,20 @@ static int get_next_block(bunzip_data *bd)
int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
{
const uint32_t *dbuf;
int pos, current, previous, gotcount;
int pos, current, previous, out_count;
uint32_t CRC;
/* If last read was short due to end of file, return last block now */
if (bd->writeCount < 0) return bd->writeCount;
/* If we already have error/end indicator, return it */
if (bd->writeCount < 0)
return bd->writeCount;
gotcount = 0;
out_count = 0;
dbuf = bd->dbuf;
/* Register-cached state (hopefully): */
pos = bd->writePos;
current = bd->writeCurrent;
CRC = bd->writeCRC; /* small loss on x86-32 (not enough regs), win on x86-64 */
/* We will always have pending decoded data to write into the output
buffer unless this is the very first call (in which case we haven't
@ -514,8 +519,8 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
/* Loop outputting bytes */
for (;;) {
/* If the output buffer is full, snapshot state and return */
if (gotcount >= len) {
/* If the output buffer is full, save cached state and return */
if (out_count >= len) {
/* Unlikely branch.
* Use of "goto" instead of keeping code here
* helps compiler to realize this. */
@ -523,17 +528,16 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
}
/* Write next byte into output buffer, updating CRC */
outbuf[gotcount++] = current;
bd->writeCRC = (bd->writeCRC << 8)
^ bd->crc32Table[(bd->writeCRC >> 24) ^ current];
outbuf[out_count++] = current;
CRC = (CRC << 8) ^ bd->crc32Table[(CRC >> 24) ^ current];
/* Loop now if we're outputting multiple copies of this byte */
if (bd->writeCopies) {
/* Unlikely branch */
/*--bd->writeCopies;*/
/*continue;*/
/* Same, but (ab)using other existing --writeCopies operation.
* Luckily, this also compiles into just one branch insn: */
/* Same, but (ab)using other existing --writeCopies operation
* (and this if() compiles into just test+branch pair): */
goto dec_writeCopies;
}
decode_next_byte:
@ -549,7 +553,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
/* After 3 consecutive copies of the same byte, the 4th
* is a repeat count. We count down from 4 instead
* of counting up because testing for non-zero is faster */
if (--bd->writeRunCountdown) {
if (--bd->writeRunCountdown != 0) {
if (current != previous)
bd->writeRunCountdown = 4;
} else {
@ -568,11 +572,11 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
} /* for(;;) */
/* Decompression of this input block completed successfully */
bd->writeCRC = ~bd->writeCRC;
bd->totalCRC = ((bd->totalCRC << 1) | (bd->totalCRC >> 31)) ^ bd->writeCRC;
bd->writeCRC = CRC = ~CRC;
bd->totalCRC = ((bd->totalCRC << 1) | (bd->totalCRC >> 31)) ^ CRC;
/* If this block had a CRC error, force file level CRC error. */
if (bd->writeCRC != bd->headerCRC) {
/* If this block had a CRC error, force file level CRC error */
if (CRC != bd->headerCRC) {
bd->totalCRC = bd->headerCRC + 1;
return RETVAL_LAST_BLOCK;
}
@ -581,23 +585,26 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
/* Refill the intermediate buffer by Huffman-decoding next block of input */
{
int r = get_next_block(bd);
if (r) {
if (r) { /* error/end */
bd->writeCount = r;
return (r != RETVAL_LAST_BLOCK) ? r : gotcount;
return (r != RETVAL_LAST_BLOCK) ? r : out_count;
}
}
bd->writeCRC = ~0;
CRC = ~0;
pos = bd->writePos;
current = bd->writeCurrent;
goto decode_next_byte;
outbuf_full:
/* Output buffer is full, snapshot state and return */
/* Output buffer is full, save cached state and return */
bd->writePos = pos;
bd->writeCurrent = current;
bd->writeCRC = CRC;
bd->writeCopies++;
return gotcount;
return out_count;
}
/* Allocate the structure, read file header. If in_fd==-1, inbuf must contain