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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>
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@ -488,18 +488,21 @@ static int get_next_block(bunzip_data *bd)
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data are written to outbuf. Return value is number of bytes written or
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error (all errors are negative numbers). If out_fd!=-1, outbuf and len
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are ignored, data is written to out_fd and return is RETVAL_OK or error.
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NB: read_bunzip returns < 0 on error, or the number of *unfilled* bytes
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in outbuf. IOW: on EOF returns len ("all bytes are not filled"), not 0.
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(Why? This allows to get rid of one local variable)
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*/
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int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
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{
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const uint32_t *dbuf;
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int pos, current, previous, out_count;
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int pos, current, previous;
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uint32_t CRC;
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/* If we already have error/end indicator, return it */
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if (bd->writeCount < 0)
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return bd->writeCount;
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out_count = 0;
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dbuf = bd->dbuf;
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/* Register-cached state (hopefully): */
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@ -520,7 +523,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
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for (;;) {
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/* If the output buffer is full, save cached state and return */
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if (out_count >= len) {
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if (--len < 0) {
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/* Unlikely branch.
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* Use of "goto" instead of keeping code here
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* helps compiler to realize this. */
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@ -528,7 +531,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
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}
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/* Write next byte into output buffer, updating CRC */
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outbuf[out_count++] = current;
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*outbuf++ = current;
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CRC = (CRC << 8) ^ bd->crc32Table[(CRC >> 24) ^ current];
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/* Loop now if we're outputting multiple copies of this byte */
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@ -587,7 +590,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
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int r = get_next_block(bd);
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if (r) { /* error/end */
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bd->writeCount = r;
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return (r != RETVAL_LAST_BLOCK) ? r : out_count;
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return (r != RETVAL_LAST_BLOCK) ? r : len;
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}
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}
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@ -604,7 +607,7 @@ int FAST_FUNC read_bunzip(bunzip_data *bd, char *outbuf, int len)
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bd->writeCopies++;
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return out_count;
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return 0;
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}
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/* Allocate the structure, read file header. If in_fd==-1, inbuf must contain
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@ -698,7 +701,10 @@ unpack_bz2_stream(int src_fd, int dst_fd)
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if (i == 0) {
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while (1) { /* "Produce some output bytes" loop */
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i = read_bunzip(bd, outbuf, IOBUF_SIZE);
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if (i <= 0)
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if (i < 0) /* error? */
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break;
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i = IOBUF_SIZE - i; /* number of bytes produced */
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if (i == 0) /* EOF? */
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break;
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if (i != full_write(dst_fd, outbuf, i)) {
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bb_error_msg("short write");
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@ -194,6 +194,8 @@ extern const llist_t *find_list_entry2(const llist_t *list, const char *filename
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/* A bit of bunzip2 internals are exposed for compressed help support: */
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typedef struct bunzip_data bunzip_data;
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int start_bunzip(bunzip_data **bdp, int in_fd, const void *inbuf, int len) FAST_FUNC;
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/* NB: read_bunzip returns < 0 on error, or the number of *unfilled* bytes
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* in outbuf. IOW: on EOF returns len ("all bytes are not filled"), not 0: */
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int read_bunzip(bunzip_data *bd, char *outbuf, int len) FAST_FUNC;
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void dealloc_bunzip(bunzip_data *bd) FAST_FUNC;
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