bf3bec51f
Denys Vlasenko
2010-10-29
Subject
decompress_bunzip2: keep bd->writeCRC in CPU reg in the hot loop
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archival/libunarchive/decompress_bunzip2.c+28 -21
| @@ -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 | |