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decompress_bunzip2: relieve register pressure in hot function read_bunzip

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function                                             old     new   delta
unpack_bz2_stream                                    318     329     +11
read_bunzip                                          268     262      -6

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
This commit is contained in:
Denys Vlasenko 2010-10-29 19:01:58 +02:00
parent bf3bec51fc
commit 1014a9adbf
2 changed files with 15 additions and 7 deletions
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20
archival/libunarchive/decompress_bunzip2.c
View File

@ -488,18 +488,21 @@ static int get_next_block(bunzip_data *bd)
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
are ignored, data is written to out_fd and return is RETVAL_OK or error.
NB: read_bunzip returns < 0 on error, or the number of *unfilled* bytes
in outbuf. IOW: on EOF returns len ("all bytes are not filled"), not 0.
(Why? This allows to get rid of one local variable)
*/
int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
{
const uint32_t *dbuf;
int pos, current, previous, out_count;
int pos, current, previous;
uint32_t CRC;
/* If we already have error/end indicator, return it */
if (bd->writeCount < 0)
return bd->writeCount;
out_count = 0;
dbuf = bd->dbuf;
/* Register-cached state (hopefully): */
@ -520,7 +523,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
for (;;) {
/* If the output buffer is full, save cached state and return */
if (out_count >= len) {
if (--len < 0) {
/* Unlikely branch.
* Use of "goto" instead of keeping code here
* helps compiler to realize this. */
@ -528,7 +531,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
}
/* Write next byte into output buffer, updating CRC */
outbuf[out_count++] = current;
*outbuf++ = current;
CRC = (CRC << 8) ^ bd->crc32Table[(CRC >> 24) ^ current];
/* Loop now if we're outputting multiple copies of this byte */
@ -587,7 +590,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
int r = get_next_block(bd);
if (r) { /* error/end */
bd->writeCount = r;
return (r != RETVAL_LAST_BLOCK) ? r : out_count;
return (r != RETVAL_LAST_BLOCK) ? r : len;
}
}
@ -604,7 +607,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
bd->writeCopies++;
return out_count;
return 0;
}
/* Allocate the structure, read file header. If in_fd==-1, inbuf must contain
@ -698,7 +701,10 @@ unpack_bz2_stream(int src_fd, int dst_fd)
if (i == 0) {
while (1) { /* "Produce some output bytes" loop */
i = read_bunzip(bd, outbuf, IOBUF_SIZE);
if (i <= 0)
if (i < 0) /* error? */
break;
i = IOBUF_SIZE - i; /* number of bytes produced */
if (i == 0) /* EOF? */
break;
if (i != full_write(dst_fd, outbuf, i)) {
bb_error_msg("short write");

2
include/unarchive.h
View File

@ -194,6 +194,8 @@ extern const llist_t *find_list_entry2(const llist_t *list, const char *filename
/* A bit of bunzip2 internals are exposed for compressed help support: */
typedef struct bunzip_data bunzip_data;
int start_bunzip(bunzip_data **bdp, int in_fd, const void *inbuf, int len) FAST_FUNC;
/* NB: read_bunzip returns < 0 on error, or the number of *unfilled* bytes
* in outbuf. IOW: on EOF returns len ("all bytes are not filled"), not 0: */
int read_bunzip(bunzip_data *bd, char *outbuf, int len) FAST_FUNC;
void dealloc_bunzip(bunzip_data *bd) FAST_FUNC;