diff --git a/c_unpacker/unpack.c b/c_unpacker/unpack.c
index e7643f3..c893d56 100644
--- a/c_unpacker/unpack.c
+++ b/c_unpacker/unpack.c
@@ -32,14 +32,18 @@ int upkr_decode_bit(int context_index) {
     int prob = upkr_probs[context_index];
     int bit = (upkr_state & 255) < prob ? 1 : 0;
     
-    if(bit) {
-        upkr_state = prob * (upkr_state >> 8) + (upkr_state & 255);
-        upkr_probs[context_index] = prob + ((256 - prob + 8) >> 4);
-    } else {
-        upkr_state = (256 - prob) * (upkr_state >> 8) + (upkr_state & 255) - prob;
-        upkr_probs[context_index] = prob - ((prob + 8) >> 4);
+    int tmp = prob;
+    if(!bit) {
+        tmp = 256 - tmp;
     }
-    
+    upkr_state = tmp * (upkr_state >> 8) + (upkr_state & 255);
+    tmp += (256 - tmp + 8) >> 4;
+    if(!bit) {
+        upkr_state -= prob;
+        tmp = 256 - tmp;
+    }
+    upkr_probs[context_index] = tmp;
+
     return bit;
 }
 
diff --git a/src/main.rs b/src/main.rs
index ae90eff..711cb32 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -16,7 +16,7 @@ fn main() -> Result<()> {
 
             let mut data = vec![];
             File::open(infile)?.read_to_end(&mut data)?;
-            
+
             let mut pb = pbr::ProgressBar::new(data.len() as u64);
             pb.set_units(pbr::Units::Bytes);
             let packed_data = upkr::pack(
@@ -58,7 +58,10 @@ fn main() -> Result<()> {
 
 fn print_help() {
     eprintln!("Usage:");
-    eprintln!("  upkr pack [-l level(0-9)] <infile> <outfile>");
-    eprintln!("  upkr unpack <infile> <outfile>");
+    eprintln!("  upkr pack [-b] [-l level(0-9)] <infile> <outfile>");
+    eprintln!("  upkr unpack [-b] <infile> <outfile>");
+    eprintln!();
+    eprintln!(" -b, --bitstream     bitstream mode");
+    eprintln!(" -l, --level N       compression level 0-9");
     std::process::exit(1);
 }