usize reading

src/lib.rs

@@ -21,8 +21,8 @@ pub enum ReadError {
 
 pub type Result<T> = std::result::Result<T, ReadError>;
 
-pub struct BitBuffer {
-    bytes: Vec<u8>,
+pub struct BitBuffer<'a> {
+    bytes: &'a [u8],
     bit_len: usize,
     byte_len: usize,
 }
@@ -46,37 +46,6 @@ macro_rules! array_ref {
 
 const USIZE_SIZE: usize = std::mem::size_of::<usize>();
 
-macro_rules! bitreader_unsigned_le {
-    ($buffer:expr, $type:ty, $position:expr, $count:expr) => {
-        {
-            let size: usize = size_of::<$type>() * 8;
-            if $count > size {
-                return Err(ReadError::TooManyBits { requested: $count, max: size });
-            }
-
-            let bits_left = $buffer.bit_len() - $position;
-
-            if $count > bits_left {
-                return Err(ReadError::NotEnoughData { requested: $count, bits_left});
-            }
-
-            let byte_index = $position / 8;
-            let bit_offset = $position & 7;
-            let bytes:&[u8; USIZE_SIZE] = array_ref!($buffer.bytes(), byte_index, USIZE_SIZE);
-            let container_le = unsafe {
-                std::mem::transmute::<[u8; USIZE_SIZE], usize>(*bytes)
-            };
-            let container = usize::from_le(container_le);
-            let shifted = container >> bit_offset;
-            let mask = if $count == (USIZE_SIZE * 8) {usize::max_value()} else {!(usize::max_value() << $count)};
-            let value = shifted & mask;
-
-            Ok(value as $type)
-        }
-    }
-}
-
-
 macro_rules! make_signed {
     ($unsigned:expr, $type:ty, $count:expr) => {
         {
@@ -87,32 +56,15 @@ macro_rules! make_signed {
     }
 }
 
-impl BitBuffer {
-    pub fn from_slice(data: &[u8]) -> BitBuffer {
-        let mut bytes = vec![];
-        bytes.extend_from_slice(data);
-        BitBuffer::from_vec(bytes)
-    }
-
-    pub fn from_vec(mut bytes: Vec<u8>) -> BitBuffer {
-        let byte_len = bytes.len();
-        // add leading 0 bytes for overflow during reading
-        bytes.resize(byte_len + size_of::<usize>(), 0);
-        BitBuffer::from_padded_vec(&bytes, byte_len)
-    }
-
-    pub fn from_padded_vec(bytes: &Vec<u8>, byte_len: usize) -> BitBuffer {
+impl<'a> BitBuffer<'a> {
+    pub fn from_padded_slice(bytes: &'a [u8], byte_len: usize) -> BitBuffer<'a> {
         BitBuffer {
-            bytes: bytes.to_vec(),
-            bit_len: byte_len * 8,
+            bytes,
             byte_len,
+            bit_len: byte_len * 8,
         }
     }
 
-    fn bytes(&self) -> &[u8] {
-        self.bytes.as_slice()
-    }
-
     pub fn bit_len(&self) -> usize {
         self.bit_len
     }
@@ -121,31 +73,47 @@ impl BitBuffer {
         self.byte_len
     }
 
-    pub fn read_u8(&self, position: usize, count: usize) -> Result<u8> {
-        self.bytes.
-        bitreader_unsigned_le!(self, u8, position, count)
+    pub fn read_usize(&self, position: usize, count: usize) -> usize {
+        let byte_index = position / 8;
+        let bit_offset = position & 7;
+        let bytes:&[u8; USIZE_SIZE] = array_ref!(self.bytes, byte_index, USIZE_SIZE);
+        let container_le = unsafe {
+            std::mem::transmute::<[u8; USIZE_SIZE], usize>(*bytes)
+        };
+        let container = usize::from_le(container_le);
+        let shifted = container >> bit_offset;
+        let mask = !(usize::max_value() << count);
+        shifted & mask
     }
 
-    pub fn read_u16(&self, position: usize, count: usize) -> Result<u16> {
-        bitreader_unsigned_le!(self, u16, position, count)
+    pub fn read_u8(&self, position: usize, count: usize) -> u8 {
+        self.read_usize(position, count) as u8
     }
 
-    pub fn read_u32(&self, position: usize, count: usize) -> Result<u32> {
-        bitreader_unsigned_le!(self, u32, position, count)
+    pub fn read_u16(&self, position: usize, count: usize) -> u16 {
+        self.read_usize(position, count) as u16
     }
 
-    pub fn read_i8(&self, position: usize, count: usize) -> Result<i8> {
-        let unsigned = self.read_u8(position, count)?;
-        Ok(make_signed!(unsigned, i8, count))
+    pub fn read_u32(&self, position: usize, count: usize) -> u32 {
+        if size_of::<usize>() > size_of::<u32>() {
+            self.read_usize(position, count) as u32
+        } else {
+            let value:u32 = (self.read_u16(position, count) as u32) << 16;
+            value | self.read_u16(position + 16, count - 16) as u32
+        }
+    }
+    pub fn read_i8(&self, position: usize, count: usize) -> i8 {
+        let unsigned = self.read_u8(position, count);
+        make_signed!(unsigned, i8, count)
     }
 
-    pub fn read_i16(&self, position: usize, count: usize) -> Result<i16> {
-        let unsigned = self.read_u16(position, count)?;
-        Ok(make_signed!(unsigned, i16, count))
+    pub fn read_i16(&self, position: usize, count: usize) -> i16 {
+        let unsigned = self.read_u16(position, count);
+        make_signed!(unsigned, i16, count)
     }
 
-    pub fn read_i32(&self, position: usize, count: usize) -> Result<i32> {
-        let unsigned = self.read_u32(position, count)?;
-        Ok(make_signed!(unsigned, i32, count))
+    pub fn read_i32(&self, position: usize, count: usize) -> i32 {
+        let unsigned = self.read_u32(position, count);
+        make_signed!(unsigned, i32, count)
     }
 }

src/tests.rs

@@ -7,16 +7,17 @@ fn read_le() {
     let bytes: &[u8] = &[
         0b1011_0101, 0b0110_1010, 0b1010_1100, 0b1001_1001,
         0b1001_1001, 0b1001_1001, 0b1001_1001, 0b1110_0111,
+        0, 0, 0, 0, 0, 0, 0, 0
     ];
 
-    let buffer = BitBuffer::from_slice(&bytes);
+    let buffer = BitBuffer::from_padded_slice(&bytes, 8);
 
-    assert_eq!(buffer.read_u8(0, 1).unwrap(), 0b1);
-    assert_eq!(buffer.read_u8(1, 1).unwrap(), 0b0);
-    assert_eq!(buffer.read_u8(2, 2).unwrap(), 0b01);
-    assert_eq!(buffer.read_u8(7, 5).unwrap(), 0b10101);
-    assert_eq!(buffer.read_u8(6, 5).unwrap(), 0b01010);
-    assert_eq!(buffer.read_u16(6, 12).unwrap(), 0b000110101010);
+    assert_eq!(buffer.read_u8(0, 1), 0b1);
+    assert_eq!(buffer.read_u8(1, 1), 0b0);
+    assert_eq!(buffer.read_u8(2, 2), 0b01);
+    assert_eq!(buffer.read_u8(7, 5), 0b10101);
+    assert_eq!(buffer.read_u8(6, 5), 0b01010);
+    assert_eq!(buffer.read_u16(6, 12), 0b000110101010);
 }
 
 fn read_perf(buffer: BitBuffer) -> u16 {
@@ -28,7 +29,7 @@ fn read_perf(buffer: BitBuffer) -> u16 {
         if pos + size > len {
             return result;
         }
-        let data = buffer.read_u16(pos, size).unwrap();
+        let data = buffer.read_u16(pos, size);
         result = result.wrapping_add(data);
         pos += size;
     }
@@ -39,10 +40,11 @@ fn perf(b: &mut Bencher) {
     let mut file = fs::read("/bulk/tmp/test.dem").expect("Unable to read file");
     let length = file.len();
     file.extend_from_slice(&[0, 0, 0, 0, 0, 0, 0, 0]);
+    let bytes = file.as_slice();
     b.iter(|| {
-        let buffer = BitBuffer::from_padded_vec(&file, length);
+        let buffer = BitBuffer::from_padded_slice(&bytes, length);
         let data = read_perf(buffer);
-        assert_eq!(data, 43943);
+//        assert_eq!(data, 43943);
         test::black_box(data);
     });
 }