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use encode::Encode;
use stream::Write;
use {Bit, DataPoint};
pub const END_MARKER: u64 = 0b1111_0000_0000_0000_0000_0000_0000_0000_0000;
pub const END_MARKER_LEN: u32 = 36;
#[derive(Debug)]
pub struct StdEncoder<T: Write> {
time: u64, delta: u64, value_bits: u64, leading_zeroes: u32,
trailing_zeroes: u32,
first: bool, w: T,
}
impl<T> StdEncoder<T>
where
T: Write,
{
pub fn new(start: u64, w: T) -> Self {
let mut e = StdEncoder {
time: start,
delta: 0,
value_bits: 0,
leading_zeroes: 64, trailing_zeroes: 64, first: true,
w,
};
e.w.write_bits(start, 64);
e
}
fn write_first(&mut self, time: u64, value_bits: u64) {
self.delta = time - self.time;
self.time = time;
self.value_bits = value_bits;
self.w.write_bit(Bit::Zero);
self.w.write_bits(self.delta, 14);
self.w.write_bits(self.value_bits, 64);
self.first = true
}
fn write_next_timestamp(&mut self, time: u64) {
let delta = time - self.time; let dod = delta.wrapping_sub(self.delta) as i32; #[cfg_attr(feature = "cargo-clippy", allow(clippy::match_overlapping_arm))]
match dod {
0 => {
self.w.write_bit(Bit::Zero);
}
-63..=64 => {
self.w.write_bits(0b10, 2);
self.w.write_bits(dod as u64, 7);
}
-255..=256 => {
self.w.write_bits(0b110, 3);
self.w.write_bits(dod as u64, 9);
}
-2047..=2048 => {
self.w.write_bits(0b1110, 4);
self.w.write_bits(dod as u64, 12);
}
_ => {
self.w.write_bits(0b1111, 4);
self.w.write_bits(dod as u64, 32);
}
}
self.delta = delta;
self.time = time;
}
fn write_next_value(&mut self, value_bits: u64) {
let xor = value_bits ^ self.value_bits;
self.value_bits = value_bits;
if xor == 0 {
self.w.write_bit(Bit::Zero);
} else {
self.w.write_bit(Bit::One);
let leading_zeroes = xor.leading_zeros();
let trailing_zeroes = xor.trailing_zeros();
if leading_zeroes >= self.leading_zeroes && trailing_zeroes >= self.trailing_zeroes {
self.w.write_bit(Bit::Zero);
self.w.write_bits(
xor.wrapping_shr(self.trailing_zeroes),
64 - self.leading_zeroes - self.trailing_zeroes,
);
} else {
self.w.write_bit(Bit::One);
self.w.write_bits(u64::from(leading_zeroes), 6);
let significant_digits = 64 - leading_zeroes - trailing_zeroes;
self.w.write_bits(u64::from(significant_digits - 1), 6);
self.w
.write_bits(xor.wrapping_shr(trailing_zeroes), significant_digits);
self.leading_zeroes = leading_zeroes;
self.trailing_zeroes = trailing_zeroes;
}
}
}
}
impl<T> Encode for StdEncoder<T>
where
T: Write,
{
fn encode(&mut self, dp: DataPoint) {
let value_bits = dp.value.to_bits();
if self.first {
self.write_first(dp.time, value_bits);
self.first = false;
return;
}
self.write_next_timestamp(dp.time);
self.write_next_value(value_bits)
}
fn close(mut self) -> Box<[u8]> {
self.w.write_bits(END_MARKER, 36);
self.w.close()
}
}
#[cfg(test)]
mod tests {
use super::StdEncoder;
use encode::Encode;
use stream::BufferedWriter;
use DataPoint;
#[test]
fn create_new_encoder() {
let w = BufferedWriter::new();
let start_time = 1482268055; let e = StdEncoder::new(start_time, w);
let bytes = e.close();
let expected_bytes: [u8; 13] = [0, 0, 0, 0, 88, 89, 157, 151, 240, 0, 0, 0, 0];
assert_eq!(bytes[..], expected_bytes[..]);
}
#[test]
fn encode_datapoint() {
let w = BufferedWriter::new();
let start_time = 1482268055; let mut e = StdEncoder::new(start_time, w);
let d1 = DataPoint::new(1482268055 + 10, 1.24);
e.encode(d1);
let bytes = e.close();
let expected_bytes: [u8; 23] = [
0, 0, 0, 0, 88, 89, 157, 151, 0, 20, 127, 231, 174, 20, 122, 225, 71, 175, 224, 0, 0,
0, 0,
];
assert_eq!(bytes[..], expected_bytes[..]);
}
#[test]
fn encode_multiple_datapoints() {
let w = BufferedWriter::new();
let start_time = 1482268055; let mut e = StdEncoder::new(start_time, w);
let d1 = DataPoint::new(1482268055 + 10, 1.24);
e.encode(d1);
let d2 = DataPoint::new(1482268055 + 20, 1.98);
let d3 = DataPoint::new(1482268055 + 32, 2.37);
let d4 = DataPoint::new(1482268055 + 44, -7.41);
let d5 = DataPoint::new(1482268055 + 52, 103.50);
e.encode(d2);
e.encode(d3);
e.encode(d4);
e.encode(d5);
let bytes = e.close();
let expected_bytes: [u8; 61] = [
0, 0, 0, 0, 88, 89, 157, 151, 0, 20, 127, 231, 174, 20, 122, 225, 71, 174, 204, 207,
30, 71, 145, 228, 121, 30, 96, 88, 61, 255, 253, 91, 214, 245, 189, 111, 91, 3, 232, 1,
245, 97, 88, 86, 21, 133, 55, 202, 1, 17, 15, 92, 40, 245, 194, 151, 128, 0, 0, 0, 0,
];
assert_eq!(bytes[..], expected_bytes[..]);
}
}