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use std::cmp::min;
use crate::{BitWriter, Compressor, CompressorConfig, Decompressor};
use crate::data_types::NumberLike;
use crate::errors::QCompressResult;
const AUTO_DELTA_LIMIT: usize = 1000;
pub fn auto_compress<T: NumberLike>(nums: &[T], compression_level: usize) -> Vec<u8> {
let compressor = Compressor::from_config(auto_compressor_config(nums, compression_level));
compressor.simple_compress(nums)
}
pub fn auto_decompress<T: NumberLike>(bytes: &[u8]) -> QCompressResult<Vec<T>> {
let decompressor = Decompressor::<T>::default();
decompressor.simple_decompress(bytes)
}
pub fn auto_compressor_config<T: NumberLike>(nums: &[T], compression_level: usize) -> CompressorConfig {
let delta_encoding_order = auto_delta_encoding_order(nums, compression_level);
CompressorConfig {
compression_level,
delta_encoding_order,
}
}
fn auto_delta_encoding_order<T: NumberLike>(
nums: &[T],
compression_level: usize,
) -> usize {
let head_nums = if nums.len() < AUTO_DELTA_LIMIT {
nums
} else {
&nums[0..AUTO_DELTA_LIMIT]
};
let mut best_order = usize::MAX;
let mut best_size = usize::MAX;
for delta_encoding_order in 0..8 {
let config = CompressorConfig {
delta_encoding_order,
compression_level: min(compression_level, 6),
};
let compressor = Compressor::<T>::from_config(config);
let mut writer = BitWriter::default();
compressor.chunk(head_nums, &mut writer).unwrap();
let size = writer.byte_size();
if size < best_size {
best_order = delta_encoding_order;
best_size = size;
} else {
break;
}
}
best_order
}
#[cfg(test)]
mod tests {
use crate::auto::auto_delta_encoding_order;
#[test]
fn test_auto_delta_encoding_order() {
let mut no_trend = Vec::new();
let mut linear_trend = Vec::new();
let mut quadratic_trend = Vec::new();
let mut m = 1;
for i in 0_i32..100_i32 {
no_trend.push(m);
m *= 77;
m %= 100;
linear_trend.push(i);
quadratic_trend.push(i * i);
}
assert_eq!(auto_delta_encoding_order(&no_trend, 3), 0);
assert_eq!(auto_delta_encoding_order(&linear_trend, 3), 1);
assert_eq!(auto_delta_encoding_order(&quadratic_trend, 3), 2);
}
}