dranke/upkr
1
0
Fork 0
mirror of https://github.com/exoticorn/upkr.git synced 2026-01-20 11:36:42 +01:00
Code Issues Projects Releases Wiki Activity

c unpacker now works

Browse Source
This commit is contained in:
Dennis Ranke
2022-09-09 00:47:33 +02:00
parent f817dc9254
commit 4903ac3786
2 changed files with 9 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
c_unpacker/readme.txt Normal file
View File

@@ -0,0 +1,4 @@
a very simple unpacker in c, as a reference for people wanting to implement their own unpacker.
absolutely not production ready, it makes no effort to ensure the output buffer can actually
hold the uncompressed data.
!!! Never run on untrusted input !!!

12
c_unpacker/unpack.c
View File

@@ -34,9 +34,9 @@ int upkr_decode_bit(int context_index) {
if(bit) { if(bit) {
upkr_state = prob * (upkr_state >> 8) + (upkr_state & 255); upkr_state = prob * (upkr_state >> 8) + (upkr_state & 255);
upkr_probs[context_index] = prob + ((255 - prob + 8) >> 4); upkr_probs[context_index] = prob + ((256 - prob + 8) >> 4);
} else { } else {
upkr_state = (255 - prob) * (upkr_state >> 8) + (upkr_state & 255) - prob; upkr_state = (256 - prob) * (upkr_state >> 8) + (upkr_state & 255) - prob;
upkr_probs[context_index] = prob - ((prob + 8) >> 4); upkr_probs[context_index] = prob - ((prob + 8) >> 4);
} }
@@ -75,20 +75,18 @@ int upkr_unpack(void* destination, void* compressed_data) {
} }
} }
int length = upkr_decode_length(257 + 64); int length = upkr_decode_length(257 + 64);
while(length-- > 1) { while(length--) {
*write_ptr = write_ptr[-offset]; *write_ptr = write_ptr[-offset];
++write_ptr; ++write_ptr;
} }
prev_was_match = 1; prev_was_match = 1;
} else { } else {
int context_index = 1; u8 context_index = 1;
int byte = 0;
for(int i = 0; i < 8; ++i) { for(int i = 0; i < 8; ++i) {
int bit = upkr_decode_bit(context_index); int bit = upkr_decode_bit(context_index);
context_index = (context_index << 1) + bit; context_index = (context_index << 1) + bit;
byte |= bit << i;
} }
*write_ptr++ = byte; *write_ptr++ = context_index;
prev_was_match = 0; prev_was_match = 0;
} }
} }