decompress_bunzip2: relieve register pressure in hot function read_bunzip
function old new delta
unpack_bz2_stream 318 329 +11
read_bunzip 268 262 -6
Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/archival/libunarchive/decompress_bunzip2.c b/archival/libunarchive/decompress_bunzip2.c
index 8d7746a..00ec47c 100644
--- a/archival/libunarchive/decompress_bunzip2.c
+++ b/archival/libunarchive/decompress_bunzip2.c
@@ -488,18 +488,21 @@
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 @@
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 @@
}
/* 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 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 @@
bd->writeCopies++;
- return out_count;
+ return 0;
}
/* Allocate the structure, read file header. If in_fd==-1, inbuf must contain
@@ -698,7 +701,10 @@
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");