denuvo-ref/precomp-cpp
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Use a histogram in brute mode

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- Prevent false positives that slow down brute mode by using a histogram that filters data too redundant for a deflate stream
This commit is contained in:
Christian Schneider 2017-08-21 06:54:43 +02:00
parent 6a6dea54a3
commit d4b0a8e58a
1 changed files with 17 additions and 1 deletions
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18
precomp.cpp
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@ -2743,13 +2743,29 @@ int inf(FILE *source, FILE *dest, int windowbits, int& compressed_stream_size) {
}
int histogram[256];
bool check_inf_result(int cb_pos, int windowbits, bool use_brute_parameters = false) {
// first check BTYPE bits, skip 11 ("reserved (error)")
int btype = (in_buf[cb_pos] & 0x07) >> 1;
if (btype == 3) return false;
// skip BTYPE = 00 ("uncompressed") only in brute mode, because these can be useful for recursion
// and often occur in combination with static/dynamic BTYPE blocks
if ((use_brute_parameters) && (btype == 0)) return false;
if (use_brute_parameters) {
if (btype == 0) return false;
// use a histogram to see if the first 64 bytes are too redundant for a deflate stream,
// if a byte is present 8 or more times, it's most likely not a deflate stream
// and could slow down the process (e.g. repeated patterns of "0xEBE1F1" or "0xEBEBEBFF"
// did this before)
for (int i = 0; i < 256; i++)
histogram[i] = 0;
for (int i = 0; i < 64; i++) {
histogram[in_buf[cb_pos + i]]++;
if (histogram[in_buf[cb_pos + i]] == 8) return false;
}
}
int ret;
unsigned have = 0;