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Speed up base32::decode()

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From 1.03% to 0.19% of the runtime of 'nix-instantiate "<nixpkgs>" -A
texlive.combined.scheme-full --dry-run'.
This commit is contained in:
Eelco Dolstra 2019-12-10 19:50:02 +01:00
parent bbe97dff8b
commit f64b58b45e
1 changed files with 17 additions and 9 deletions
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26
nix-rust/src/util/base32.rs
View file

@ -1,5 +1,4 @@
use crate::error::Error;
use std::collections::HashMap;
pub fn encoded_len(input_len: usize) -> usize {
if input_len == 0 {
@ -9,14 +8,20 @@ pub fn encoded_len(input_len: usize) -> usize {
}
}
pub fn decoded_len(input_len: usize) -> usize {
input_len * 5 / 8
}
static BASE32_CHARS: &'static [u8; 32] = &b"0123456789abcdfghijklmnpqrsvwxyz";
lazy_static! {
static ref BASE32_CHARS_REVERSE: HashMap<char, u8> = BASE32_CHARS
.iter()
.enumerate()
.map(|(n, c)| (*c as char, n as u8))
.collect();
static ref BASE32_CHARS_REVERSE: Box<[u8; 256]> = {
let mut xs = [0xffu8; 256];
for (n, c) in BASE32_CHARS.iter().enumerate() {
xs[*c as usize] = n as u8;
}
Box::new(xs)
};
}
pub fn encode(input: &[u8]) -> String {
@ -44,14 +49,17 @@ pub fn encode(input: &[u8]) -> String {
}
pub fn decode(input: &str) -> Result<Vec<u8>, crate::Error> {
let mut res = Vec::new();
let mut res = Vec::with_capacity(decoded_len(input.len()));
let mut nr_bits_left: usize = 0;
let mut bits_left: u16 = 0;
for c in input.chars().rev() {
let x = BASE32_CHARS_REVERSE.get(&c).ok_or(Error::BadBase32)?;
bits_left |= (*x as u16) << nr_bits_left;
let b = BASE32_CHARS_REVERSE[c as usize];
if b == 0xff {
return Err(Error::BadBase32);
}
bits_left |= (b as u16) << nr_bits_left;
nr_bits_left += 5;
if nr_bits_left >= 8 {
res.push((bits_left & 0xff) as u8);