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refactor(nix-compat/nixbase32): clean up encode

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Change-Id: I63da5bd47cd9033e1cc13fbe4b4864514a5343cb
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9865
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
This commit is contained in:
edef 2023-10-27 17:06:29 +00:00
parent 2fce356ce0
commit 3a77e55d2c
1 changed files with 14 additions and 15 deletions
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29
tvix/nix-compat/src/nixbase32.rs
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@ -29,24 +29,23 @@ pub fn encode(input: &[u8]) -> String {
let output_len = encode_len(input.len());
let mut output = String::with_capacity(output_len);
if output_len > 0 {
for n in (0..=output_len - 1).rev() {
let b = n * 5; // bit offset within the entire input
let i = b / 8; // input byte index
let j = b % 8; // bit offset within that input byte
for n in (0..output_len).rev() {
let b = n * 5; // bit offset within the entire input
let i = b / 8; // input byte index
let j = b % 8; // bit offset within that input byte
let mut c = input[i] >> j;
if i + 1 < input.len() {
// we want to right shift, and discard shifted out bits (unchecked)
// To do this without panicing, we need to do the shifting in u16
// and convert back to u8 afterwards.
c |= ((input[i + 1] as u16) << (8 - j as u16)) as u8
// 5-bit words aren't aligned to bytes
// we can only read byte-aligned units
// read 16 bits then shift and mask to 5
let c = {
let mut word = input[i] as u16;
if let Some(&msb) = input.get(i + 1) {
word |= (msb as u16) << 8;
}
(word >> j) & 0x1f
};
output
.write_char(ALPHABET[(c & 0x1f) as usize] as char)
.unwrap();
}
output.write_char(ALPHABET[c as usize] as char).unwrap();
}
output