remove extra bounds check in stream

this is done by
 - making the buffer cloneable
 - allow getting a clone of the buffer with a shorter length
 - use the shorter buffer when reading a sub-stream

that way the bounds checks in the buffer are enough to bounds check sub-streams

src/buffer.rs

@@ -4,6 +4,7 @@ use std::fmt::Debug;
 use std::marker::PhantomData;
 use std::mem::size_of;
 use std::ops::BitOrAssign;
+use std::rc::Rc;
 
 use num_traits::{Float, PrimInt};
 
@@ -37,7 +38,7 @@ pub struct BitBuffer<E>
 where
     E: Endianness,
 {
-    bytes: Vec<u8>,
+    bytes: Rc<Vec<u8>>,
     bit_len: usize,
     byte_len: usize,
     endianness: PhantomData<E>,
@@ -63,7 +64,7 @@ where
     pub fn new(bytes: Vec<u8>, _endianness: E) -> Self {
         let byte_len = bytes.len();
         BitBuffer {
-            bytes,
+            bytes: Rc::new(bytes),
             byte_len,
             bit_len: byte_len * 8,
             endianness: PhantomData,
@@ -439,13 +440,54 @@ where
             Ok(T::from_f64_unchecked(f64::from_bits(int)))
         }
     }
+
+    /// Get a clone of the buffer with a shorter length
+    ///
+    /// # Errors
+    ///
+    /// - [`ReadError::NotEnoughData`]: if the requested length is higher than the buffer length
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use bitstream_reader::{BitBuffer, LittleEndian, Result};
+    /// #
+    /// # fn main() -> Result<()> {
+    /// # let bytes = vec![
+    /// #     0b1011_0101, 0b0110_1010, 0b1010_1100, 0b1001_1001,
+    /// #     0b1001_1001, 0b1001_1001, 0b1001_1001, 0b1110_0111
+    /// # ];
+    /// # let buffer = BitBuffer::new(bytes, LittleEndian);
+    /// let sub = buffer.get_sub_buffer(16)?;
+    /// let result: u8 = sub.read_int(0, 6)?;
+    /// #
+    /// #     Ok(())
+    /// # }
+    /// ```
+    ///
+    /// [`ReadError::NotEnoughData`]: enum.ReadError.html#variant.NotEnoughData
+    pub fn get_sub_buffer(&self, bit_len: usize) -> Result<Self> {
+        if bit_len > self.bit_len {
+            return Err(ReadError::NotEnoughData {
+                requested: bit_len,
+                bits_left: self.bit_len,
+            });
+        }
+
+        Ok(BitBuffer {
+            bytes: Rc::clone(&self.bytes),
+            byte_len: bit_len / 8,
+            bit_len,
+            endianness: PhantomData,
+        })
+    }
 }
 
 impl<E: Endianness> From<Vec<u8>> for BitBuffer<E> {
     fn from(bytes: Vec<u8>) -> Self {
         let byte_len = bytes.len();
         BitBuffer {
-            bytes,
+            bytes: Rc::new(bytes),
             byte_len,
             bit_len: byte_len * 8,
             endianness: PhantomData,
@@ -453,6 +495,17 @@ impl<E: Endianness> From<Vec<u8>> for BitBuffer<E> {
     }
 }
 
+impl<E: Endianness> Clone for BitBuffer<E> {
+    fn clone(&self) -> Self {
+        BitBuffer {
+            bytes: Rc::clone(&self.bytes),
+            byte_len: self.byte_len,
+            bit_len: self.bit_len,
+            endianness: PhantomData,
+        }
+    }
+}
+
 impl<E: Endianness> Debug for BitBuffer<E> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(

src/stream.rs

@@ -1,6 +1,5 @@
 use std::mem::size_of;
 use std::ops::BitOrAssign;
-use std::rc::Rc;
 
 use num_traits::{Float, PrimInt};
 
@@ -31,7 +30,7 @@ pub struct BitStream<E>
 where
     E: Endianness,
 {
-    buffer: Rc<BitBuffer<E>>,
+    buffer: BitBuffer<E>,
     start_pos: usize,
     pos: usize,
     bit_len: usize,
@@ -62,18 +61,7 @@ where
             start_pos: 0,
             pos: 0,
             bit_len: buffer.bit_len(),
-            buffer: Rc::new(buffer),
-        }
-    }
-
-    fn verify_bits_left(&self, count: usize) -> Result<()> {
-        if self.bits_left() < count {
-            Err(ReadError::NotEnoughData {
-                bits_left: self.bits_left(),
-                requested: count,
-            })
-        } else {
-            Ok(())
+            buffer,
         }
     }
 
@@ -105,7 +93,6 @@ where
     ///
     /// [`ReadError::NotEnoughData`]: enum.ReadError.html#variant.NotEnoughData
     pub fn read_bool(&mut self) -> Result<bool> {
-        self.verify_bits_left(1)?;
         let result = self.buffer.read_bool(self.pos);
         if result.is_ok() {
             self.pos += 1;
@@ -146,7 +133,6 @@ where
     where
         T: PrimInt + BitOrAssign + IsSigned + UncheckedPrimitiveInt,
     {
-        self.verify_bits_left(count)?;
         let result = self.buffer.read_int(self.pos, count);
         if result.is_ok() {
             self.pos += count;
@@ -185,7 +171,6 @@ where
         T: Float + UncheckedPrimitiveFloat,
     {
         let count = size_of::<T>() * 8;
-        self.verify_bits_left(count)?;
         let result = self.buffer.read_float(self.pos);
         if result.is_ok() {
             self.pos += count;
@@ -221,7 +206,6 @@ where
     /// [`ReadError::NotEnoughData`]: enum.ReadError.html#variant.NotEnoughData
     pub fn read_bytes(&mut self, byte_count: usize) -> Result<Vec<u8>> {
         let count = byte_count * 8;
-        self.verify_bits_left(count)?;
         let result = self.buffer.read_bytes(self.pos, byte_count);
         if result.is_ok() {
             self.pos += count;
@@ -305,6 +289,7 @@ where
     /// assert_eq!(bits.bit_len(), 3);
     /// assert_eq!(stream.read_int::<u8>(3)?, 0b110);
     /// assert_eq!(bits.read_int::<u8>(3)?, 0b101);
+    /// assert_eq!(true, bits.read_int::<u8>(1).is_err());
     /// #
     /// #     Ok(())
     /// # }
@@ -312,9 +297,8 @@ where
     ///
     /// [`ReadError::NotEnoughData`]: enum.ReadError.html#variant.NotEnoughData
     pub fn read_bits(&mut self, count: usize) -> Result<Self> {
-        self.verify_bits_left(count)?;
         let result = BitStream {
-            buffer: Rc::clone(&self.buffer),
+            buffer: self.buffer.get_sub_buffer(self.pos + count)?,
             start_pos: self.pos,
             pos: self.pos,
             bit_len: count,
@@ -351,7 +335,6 @@ where
     ///
     /// [`ReadError::NotEnoughData`]: enum.ReadError.html#variant.NotEnoughData
     pub fn skip(&mut self, count: usize) -> Result<()> {
-        self.verify_bits_left(count)?;
         self.pos += count;
         Ok(())
     }
@@ -523,7 +506,7 @@ where
 impl<E: Endianness> Clone for BitStream<E> {
     fn clone(&self) -> Self {
         BitStream {
-            buffer: Rc::clone(&self.buffer),
+            buffer: self.buffer.clone(),
             start_pos: self.pos,
             pos: self.pos,
             bit_len: self.bit_len,