improve bit reading functionality

2 files changed, 24 insertions, 16 deletions

diff --git a/src/io/bitreader.rs b/src/io/bitreader.rs
index 8851926..b3e478e 100644
--- a/src/io/bitreader.rs
+++ b/src/io/bitreader.rs
@@ -196,6 +196,29 @@ impl<'a> BitReader<'a> {
         self.pos = ((nbits / 32) * 4) as usize;
         self.skip(nbits & 0x1F)
     }
+
+    pub fn align(&mut self) {
+        let pos = self.bits & 7;
+        if pos != 0 {
+            self.skip_cache(pos);
+        }
+    }
+}
+
+pub fn reverse_bits(inval: u32, len: u8) -> u32 {
+    if len == 0 { return 0; }
+    const REV_TAB: [u8; 16] = [
+        0b0000, 0b1000, 0b0100, 0b1100, 0b0010, 0b1010, 0b0110, 0b1110,
+        0b0001, 0b1001, 0b0101, 0b1101, 0b0011, 0b1011, 0b0111, 0b1111,
+    ];
+
+    let mut ret = 0;
+    let mut val = inval;
+    for _ in 0..8 {
+        ret = (ret << 4) | (REV_TAB[(val & 0xF) as usize] as u32);
+        val = val >> 4;
+    }
+    ret >> (32 - len)
 }
 
 #[cfg(test)]
diff --git a/src/io/codebook.rs b/src/io/codebook.rs
index 0e03ded..89641f2 100644
--- a/src/io/codebook.rs
+++ b/src/io/codebook.rs
@@ -46,21 +46,6 @@ pub trait CodebookReader<S> {
     fn read_cb(&mut self, cb: &Codebook<S>) -> CodebookResult<S>;
 }
 
-pub fn reverse_bits(inval: u32) -> u32 {
-    const REV_TAB: [u8; 16] = [
-        0b0000, 0b1000, 0b0100, 0b1100, 0b0010, 0b1010, 0b0110, 0b1110,
-        0b0001, 0b1001, 0b0101, 0b1101, 0b0011, 0b1011, 0b0111, 0b1111,
-    ];
-
-    let mut ret = 0;
-    let mut val = inval;
-    for _ in 0..8 {
-        ret = (ret << 4) | (REV_TAB[(val & 0xF) as usize] as u32);
-        val = val >> 4;
-    }
-    ret
-}
-
 const TABLE_FILL_VALUE: u32 = 0x7F;
 const MAX_LUT_BITS: u8 = 10;
 
@@ -376,7 +361,7 @@ mod test {
         assert_eq!(br2.read_cb(&cb).unwrap(), 5);
         assert_eq!(br2.read_cb(&cb).unwrap(), 8);
 
-        assert_eq!(reverse_bits(0b0000_0101_1011_1011_1101_1111_0111_1111),
+        assert_eq!(reverse_bits(0b0000_0101_1011_1011_1101_1111_0111_1111, 32),
                                 0b1111_1110_1111_1011_1101_1101_1010_0000);
 
         const BITS_LE: [u8; 3] = [0b11101111, 0b01110010, 0b01];