65 lines
1.5 KiB
Rust
65 lines
1.5 KiB
Rust
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use std::iter::FromIterator;
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use crate::descriptor::Error;
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const INPUT_CHARSET: &str = "0123456789()[],'/*abcdefgh@:$%{}IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~ijklmnopqrstuvwxyzABCDEFGH`#\"\\ ";
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const CHECKSUM_CHARSET: &str = "qpzry9x8gf2tvdw0s3jn54khce6mua7l";
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fn poly_mod(mut c: u64, val: u64) -> u64 {
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let c0 = c >> 35;
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c = ((c & 0x7ffffffff) << 5) ^ val;
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if c0 & 1 > 0 {
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c ^= 0xf5dee51989
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};
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if c0 & 2 > 0 {
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c ^= 0xa9fdca3312
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};
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if c0 & 4 > 0 {
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c ^= 0x1bab10e32d
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};
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if c0 & 8 > 0 {
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c ^= 0x3706b1677a
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};
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if c0 & 16 > 0 {
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c ^= 0x644d626ffd
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};
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c
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}
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pub fn get_checksum(desc: &str) -> Result<String, Error> {
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let mut c = 1;
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let mut cls = 0;
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let mut clscount = 0;
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for ch in desc.chars() {
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let pos = INPUT_CHARSET
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.find(ch)
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.ok_or(Error::InvalidDescriptorCharacter(ch))? as u64;
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c = poly_mod(c, pos & 31);
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cls = cls * 3 + (pos >> 5);
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clscount += 1;
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if clscount == 3 {
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c = poly_mod(c, cls);
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cls = 0;
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clscount = 0;
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}
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}
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if clscount > 0 {
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c = poly_mod(c, cls);
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}
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(0..8).for_each(|_| c = poly_mod(c, 0));
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c ^= 1;
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let mut chars = Vec::with_capacity(8);
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for j in 0..8 {
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chars.push(
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CHECKSUM_CHARSET
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.chars()
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.nth(((c >> (5 * (7 - j))) & 31) as usize)
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.unwrap(),
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);
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}
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Ok(String::from_iter(chars))
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}
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