forked from lix-project/lix
Speed up base32::decode()
From 1.03% to 0.19% of the runtime of 'nix-instantiate "<nixpkgs>" -A texlive.combined.scheme-full --dry-run'.
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@ -1,5 +1,4 @@
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use crate::error::Error;
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use std::collections::HashMap;
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pub fn encoded_len(input_len: usize) -> usize {
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if input_len == 0 {
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@ -9,14 +8,20 @@ pub fn encoded_len(input_len: usize) -> usize {
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}
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}
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pub fn decoded_len(input_len: usize) -> usize {
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input_len * 5 / 8
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}
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static BASE32_CHARS: &'static [u8; 32] = &b"0123456789abcdfghijklmnpqrsvwxyz";
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lazy_static! {
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static ref BASE32_CHARS_REVERSE: HashMap<char, u8> = BASE32_CHARS
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.iter()
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.enumerate()
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.map(|(n, c)| (*c as char, n as u8))
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.collect();
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static ref BASE32_CHARS_REVERSE: Box<[u8; 256]> = {
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let mut xs = [0xffu8; 256];
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for (n, c) in BASE32_CHARS.iter().enumerate() {
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xs[*c as usize] = n as u8;
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}
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Box::new(xs)
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};
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}
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pub fn encode(input: &[u8]) -> String {
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@ -44,14 +49,17 @@ pub fn encode(input: &[u8]) -> String {
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}
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pub fn decode(input: &str) -> Result<Vec<u8>, crate::Error> {
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let mut res = Vec::new();
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let mut res = Vec::with_capacity(decoded_len(input.len()));
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let mut nr_bits_left: usize = 0;
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let mut bits_left: u16 = 0;
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for c in input.chars().rev() {
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let x = BASE32_CHARS_REVERSE.get(&c).ok_or(Error::BadBase32)?;
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bits_left |= (*x as u16) << nr_bits_left;
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let b = BASE32_CHARS_REVERSE[c as usize];
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if b == 0xff {
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return Err(Error::BadBase32);
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}
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bits_left |= (b as u16) << nr_bits_left;
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nr_bits_left += 5;
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if nr_bits_left >= 8 {
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res.push((bits_left & 0xff) as u8);
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