6ba6a6f28
Denys Vlasenko
2018-01-30
Subject
gzip: use wider (32-bit, not 16) bi_buf
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Commit Diff GitHub →
archival/gzip.c+22 -11
| @@ -355,7 +355,7 @@ struct globals { | |
| /* Output buffer. bits are inserted starting at the bottom (least significant | |
| * bits). | |
| */ | |
| - | unsigned short bi_buf; |
| + | unsigned bi_buf; /* was unsigned short */ |
| #undef BUF_SIZE | |
| #define BUF_SIZE (int)(8 * sizeof(G1.bi_buf)) | |
| @@ -530,17 +530,25 @@ static void send_bits(int value, int length) | |
| Assert(length > 0 && length <= 15, "invalid length"); | |
| G1.bits_sent += length; | |
| #endif | |
| + | BUILD_BUG_ON(BUF_SIZE != 32 && BUF_SIZE != 16); |
| new_buf = G1.bi_buf | (value << G1.bi_valid); | |
| + | /* NB: the above may sometimes do "<< 32" shift (undefined) |
| + | * if check below is changed to "length > remain" instead of >= */ |
| remain = BUF_SIZE - G1.bi_valid; | |
| - | /* If not enough room in bi_buf */ |
| - | if (length > remain) { |
| + | |
| + | /* If bi_buf is full */ |
| + | if (length >= remain) { |
| /* ...use (valid) bits from bi_buf and | |
| - | * (16 - bi_valid) bits from value, |
| - | * leaving (width - (16-bi_valid)) unused bits in value. |
| + | * (BUF_SIZE - bi_valid) bits from value, |
| + | * leaving (width - (BUF_SIZE-bi_valid)) unused bits in value. |
| */ | |
| - | put_16bit(new_buf); |
| - | new_buf = (ush) value >> remain; |
| + | if (BUF_SIZE == 32) { |
| + | put_32bit(new_buf); /* maybe unroll to 2*put_16bit()? */ |
| + | } else { /* 16 */ |
| + | put_16bit(new_buf); |
| + | } |
| + | new_buf = (unsigned) value >> remain; |
| length -= BUF_SIZE; | |
| } | |
| G1.bi_buf = new_buf; | |
| @@ -571,10 +579,13 @@ static unsigned bi_reverse(unsigned code, int len) | |
| */ | |
| static void bi_windup(void) | |
| { | |
| - | if (G1.bi_valid > 8) { |
| - | put_16bit(G1.bi_buf); |
| - | } else if (G1.bi_valid > 0) { |
| - | put_8bit(G1.bi_buf); |
| + | unsigned bits = G1.bi_buf; |
| + | int cnt = G1.bi_valid; |
| + | |
| + | while (cnt > 0) { |
| + | put_8bit(bits); |
| + | bits >>= 8; |
| + | cnt -= 8; |
| } | |
| G1.bi_buf = 0; | |
| G1.bi_valid = 0; | |