1014a9adb
Denys Vlasenko
2010-10-29
Subject
decompress_bunzip2: relieve register pressure in hot function read_bunzip
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archival/libunarchive/decompress_bunzip2.c+13 -7
| @@ -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"); | |
include/unarchive.h+2 -0
| @@ -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; | |