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unlzma: fix erroneous "while" instead of "if". Closes 4682

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These parts of the code essentially check whether
stepping back by rep0 goes negative or not.

LZMA SDK from lzma1604.7z has the following in the corresponding places:

... = dic[dicPos - rep0 + (dicPos < rep0 ? dicBufSize : 0)]

Clearly, not loop here.

Technically, "while" here works: if condition is false (because pos
underflowed), it iterates once, adds header.dict_size (a.k.a. dicBufSize),
this makes pos positive but smaller than header.dict_size, and loop exits.

Now we'll just check for negative result of subtraction, which is less code:

function                                             old     new   delta
unpack_lzma_stream                                  2659    2641     -18

(I hope 2 Gbyte+ dictionaries won't be in use soon).

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2017-01-09 13:55:11 +01:00
parent 8c1d857d25
commit 3989e5adf4
1 changed files with 8 additions and 5 deletions
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13
archival/libarchive/decompress_unlzma.c
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@ -278,9 +278,10 @@ unpack_lzma_stream(transformer_state_t *xstate)
if (state >= LZMA_NUM_LIT_STATES) {
int match_byte;
uint32_t pos = buffer_pos - rep0;
uint32_t pos;
while (pos >= header.dict_size)
pos = buffer_pos - rep0;
if ((int32_t)pos < 0)
pos += header.dict_size;
match_byte = buffer[pos];
do {
@ -336,9 +337,11 @@ unpack_lzma_stream(transformer_state_t *xstate)
);
if (!rc_is_bit_1(rc, prob2)) {
#if ENABLE_FEATURE_LZMA_FAST
uint32_t pos = buffer_pos - rep0;
uint32_t pos;
state = state < LZMA_NUM_LIT_STATES ? 9 : 11;
while (pos >= header.dict_size)
pos = buffer_pos - rep0;
if ((int32_t)pos < 0)
pos += header.dict_size;
previous_byte = buffer[pos];
goto one_byte1;
@ -432,7 +435,7 @@ unpack_lzma_stream(transformer_state_t *xstate)
IF_NOT_FEATURE_LZMA_FAST(string:)
do {
uint32_t pos = buffer_pos - rep0;
while (pos >= header.dict_size)
if ((int32_t)pos < 0)
pos += header.dict_size;
previous_byte = buffer[pos];
IF_NOT_FEATURE_LZMA_FAST(one_byte2:)