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|
use byteorder::{ByteOrder, LittleEndian, WriteBytesExt};
use std::io;
use std::ops::Deref;
pub(crate) struct BitPacker {
mini_buffer: u64,
mini_buffer_written: usize,
}
impl BitPacker {
pub fn new() -> BitPacker {
BitPacker {
mini_buffer: 0u64,
mini_buffer_written: 0,
}
}
pub fn write<TWrite: io::Write>(
&mut self,
val: u64,
num_bits: u8,
output: &mut TWrite,
) -> io::Result<()> {
let val_u64 = val as u64;
let num_bits = num_bits as usize;
if self.mini_buffer_written + num_bits > 64 {
self.mini_buffer |= val_u64.wrapping_shl(self.mini_buffer_written as u32);
output.write_u64::<LittleEndian>(self.mini_buffer)?;
self.mini_buffer = val_u64.wrapping_shr((64 - self.mini_buffer_written) as u32);
self.mini_buffer_written = self.mini_buffer_written + num_bits - 64;
} else {
self.mini_buffer |= val_u64 << self.mini_buffer_written;
self.mini_buffer_written += num_bits;
if self.mini_buffer_written == 64 {
output.write_u64::<LittleEndian>(self.mini_buffer)?;
self.mini_buffer_written = 0;
self.mini_buffer = 0u64;
}
}
Ok(())
}
pub fn flush<TWrite: io::Write>(&mut self, output: &mut TWrite) -> io::Result<()> {
if self.mini_buffer_written > 0 {
let num_bytes = (self.mini_buffer_written + 7) / 8;
let mut arr: [u8; 8] = [0u8; 8];
LittleEndian::write_u64(&mut arr, self.mini_buffer);
output.write_all(&arr[..num_bytes])?;
self.mini_buffer_written = 0;
}
Ok(())
}
pub fn close<TWrite: io::Write>(&mut self, output: &mut TWrite) -> io::Result<()> {
self.flush(output)?;
// Padding the write file to simplify reads.
output.write_all(&[0u8; 7])?;
Ok(())
}
}
#[derive(Clone)]
pub struct BitUnpacker<Data>
where
Data: Deref<Target = [u8]>,
{
num_bits: u64,
mask: u64,
data: Data,
}
impl<Data> BitUnpacker<Data>
where
Data: Deref<Target = [u8]>,
{
pub fn new(data: Data, num_bits: u8) -> BitUnpacker<Data> {
let mask: u64 = if num_bits == 64 {
!0u64
} else {
(1u64 << num_bits) - 1u64
};
BitUnpacker {
num_bits: u64::from(num_bits),
mask,
data,
}
}
pub fn get(&self, idx: u64) -> u64 {
if self.num_bits == 0 {
return 0u64;
}
let data: &[u8] = &*self.data;
let num_bits = self.num_bits;
let mask = self.mask;
let addr_in_bits = idx * num_bits;
let addr = addr_in_bits >> 3;
let bit_shift = addr_in_bits & 7;
debug_assert!(
addr + 8 <= data.len() as u64,
"The fast field field should have been padded with 7 bytes."
);
let val_unshifted_unmasked: u64 = LittleEndian::read_u64(&data[(addr as usize)..]);
let val_shifted = (val_unshifted_unmasked >> bit_shift) as u64;
val_shifted & mask
}
}
#[cfg(test)]
mod test {
use super::{BitPacker, BitUnpacker};
fn create_fastfield_bitpacker(len: usize, num_bits: u8) -> (BitUnpacker<Vec<u8>>, Vec<u64>) {
let mut data = Vec::new();
let mut bitpacker = BitPacker::new();
let max_val: u64 = (1u64 << num_bits as u64) - 1u64;
let vals: Vec<u64> = (0u64..len as u64)
.map(|i| if max_val == 0 { 0 } else { i % max_val })
.collect();
for &val in &vals {
bitpacker.write(val, num_bits, &mut data).unwrap();
}
bitpacker.close(&mut data).unwrap();
assert_eq!(data.len(), ((num_bits as usize) * len + 7) / 8 + 7);
let bitunpacker = BitUnpacker::new(data, num_bits);
(bitunpacker, vals)
}
fn test_bitpacker_util(len: usize, num_bits: u8) {
let (bitunpacker, vals) = create_fastfield_bitpacker(len, num_bits);
for (i, val) in vals.iter().enumerate() {
assert_eq!(bitunpacker.get(i as u64), *val);
}
}
#[test]
fn test_bitpacker() {
test_bitpacker_util(10, 3);
test_bitpacker_util(10, 0);
test_bitpacker_util(10, 1);
test_bitpacker_util(6, 14);
test_bitpacker_util(1000, 14);
}
}
|
