core: add bit writer module

2 files changed, 203 insertions, 0 deletions

diff --git a/nihav-core/src/io/bitwriter.rs b/nihav-core/src/io/bitwriter.rs
new file mode 100644
index 0000000..4447567
--- /dev/null
+++ b/nihav-core/src/io/bitwriter.rs
@@ -0,0 +1,202 @@
+//! Bitstream writer functionality.
+//!
+//! Bitstream writer works on `Vec<u8>` and allows to write bits in different modes.
+//!
+//! # Examples
+//!
+//! Writing 17-bit value:
+//! ```
+//! use nihav_core::io::bitwriter::{BitWriter,BitWriterMode};
+//!
+//! # fn foo() -> Vec<u8> {
+//! let mut bw = BitWriter::new(Vec::new(), BitWriterMode::BE);
+//! bw.write(42, 17);
+//! # bw.end()
+//! # }
+//! ```
+
+/// Bitstream writing modes.
+#[derive(Debug,Clone,Copy,PartialEq)]
+pub enum BitWriterMode {
+    /// The stream is big endian MSB first.
+    BE,
+    /// The stream is little endian LSB first.
+    LE,
+    /// The stream is packed into 16-bit little-endian words MSB first.
+    LE16MSB,
+    /// The stream is packed into 32-bit little-endian words MSB first.
+    LE32MSB,
+}
+
+impl BitWriterMode {
+    fn is_be(self) -> bool { self != BitWriterMode::LE }
+}
+
+/// Bitstream writer.
+pub struct BitWriter {
+    dst:    Vec<u8>,
+    bitbuf: u32,
+    bits:   u8,
+    start:  usize,
+    mode:   BitWriterMode,
+}
+
+impl BitWriter {
+    /// Creates a new instance of `BitWriter` that will append data to the input vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use nihav_core::io::bitwriter::{BitWriter,BitWriterMode};
+    ///
+    /// let mut bw = BitWriter::new(Vec::with_capacity(100), BitWriterMode::BE);
+    /// ```
+    pub fn new(dst: Vec<u8>, mode: BitWriterMode) -> Self {
+        let start = dst.len();
+        Self {
+            dst,
+            mode,
+            start,
+            bitbuf: 0,
+            bits:   0,
+        }
+    }
+    /// Writes single zero bit to the output.
+    pub fn write0(&mut self) { self.write_bit(false); }
+    /// Writes single set bit to the output.
+    pub fn write1(&mut self) { self.write_bit(true); }
+    /// Writes single bit.
+    pub fn write_bit(&mut self, bit: bool) {
+        if self.mode.is_be() {
+            self.bitbuf |= (bit as u32) << (31 - self.bits);
+        } else {
+            self.bitbuf |= (bit as u32) << self.bits;
+        }
+        self.bits += 1;
+        self.flush();
+    }
+    /// Writes `bits` bits of `val` value to the output.
+    #[allow(clippy::collapsible_if)]
+    pub fn write(&mut self, val: u32, bits: u8) {
+        if bits == 0 {
+            return;
+        }
+        if self.mode.is_be() {
+            if self.bits + bits <= 32 {
+                self.bitbuf |= val << (32 - self.bits - bits);
+                self.bits += bits;
+                self.flush();
+            } else {
+                let cbits = 32 - self.bits;
+                let bits2 = bits - cbits;
+                self.write(val >> bits2, cbits);
+                self.write(val & ((1 << bits2) - 1), bits2);
+            }
+        } else {
+            if self.bits + bits <= 32 {
+                self.bitbuf |= val << self.bits;
+                self.bits += bits;
+                self.flush();
+            } else {
+                let cbits = 32 - self.bits;
+                let bits2 = bits - cbits;
+                self.write(val & ((1 << cbits) - 1), cbits);
+                self.write(val >> cbits, bits2);
+            }
+        }
+    }
+    /// Writes `bits` bits of signed `val` value to the output.
+    pub fn write_s(&mut self, val: i32, bits: u8) {
+        self.write((val as u32) & ((1 << bits) - 1), bits);
+    }
+    /// Tells the amount of bits written so far.
+    pub fn tell(&self) -> usize {
+        (self.dst.len() - self.start) * 8 + (self.bits as usize)
+    }
+    fn flush(&mut self) {
+        match self.mode {
+            BitWriterMode::BE => {
+                while self.bits >= 8 {
+                    self.dst.push((self.bitbuf >> 24) as u8);
+                    self.bitbuf <<= 8;
+                    self.bits    -= 8;
+                }
+            },
+            BitWriterMode::LE => {
+                while self.bits >= 8 {
+                    self.dst.push(self.bitbuf as u8);
+                    self.bitbuf >>= 8;
+                    self.bits    -= 8;
+                }
+            },
+            BitWriterMode::LE16MSB => {
+                while self.bits >= 16 {
+                    self.dst.push((self.bitbuf >> 16) as u8);
+                    self.dst.push((self.bitbuf >> 24) as u8);
+                    self.bitbuf <<= 16;
+                    self.bits    -= 16;
+                }
+            },
+            BitWriterMode::LE32MSB => {
+                if self.bits == 32 {
+                    self.dst.push( self.bitbuf        as u8);
+                    self.dst.push((self.bitbuf >>  8) as u8);
+                    self.dst.push((self.bitbuf >> 16) as u8);
+                    self.dst.push((self.bitbuf >> 24) as u8);
+                    self.bitbuf = 0;
+                    self.bits   = 0;
+                }
+            },
+        };
+    }
+    /// Finalises operations and returns the vector containing output data.
+    pub fn end(mut self) -> Vec<u8> {
+        self.flush();
+        if self.bits > 0 {
+            match self.mode {
+                BitWriterMode::BE => {
+                    self.dst.push((self.bitbuf >> 24) as u8);
+                },
+                BitWriterMode::LE => {
+                    self.dst.push(self.bitbuf as u8);
+                },
+                BitWriterMode::LE16MSB => {
+                    self.dst.push((self.bitbuf >> 16) as u8);
+                    self.dst.push((self.bitbuf >> 24) as u8);
+                },
+                BitWriterMode::LE32MSB => {
+                    self.dst.push( self.bitbuf        as u8);
+                    self.dst.push((self.bitbuf >>  8) as u8);
+                    self.dst.push((self.bitbuf >> 16) as u8);
+                    self.dst.push((self.bitbuf >> 24) as u8);
+                },
+            };
+        }
+        self.dst
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn bw_works() {
+        let mut bw = BitWriter::new(Vec::new(), BitWriterMode::BE);
+        bw.write(43, 9);
+        let data = bw.end();
+        assert_eq!(&data, &[21, 128]);
+
+        let mut bw = BitWriter::new(Vec::new(), BitWriterMode::LE);
+        bw.write1();
+        bw.write(43, 9);
+        let data = bw.end();
+        assert_eq!(&data, &[87, 0]);
+
+        let mut bw = BitWriter::new(Vec::new(), BitWriterMode::LE32MSB);
+        bw.write(42, 9);
+        bw.write(42, 9);
+        let data = bw.end();
+        assert_eq!(&data, &[0, 128, 10, 21]);
+    }
+}
diff --git a/nihav-core/src/io/mod.rs b/nihav-core/src/io/mod.rs
index 81ce35e..b7bcafe 100644
--- a/nihav-core/src/io/mod.rs
+++ b/nihav-core/src/io/mod.rs
@@ -1,5 +1,6 @@
 //! Byte- and bitstream reading/writing functionality.
 pub mod bitreader;
+pub mod bitwriter;
 pub mod codebook;
 pub mod intcode;
 pub mod byteio;