47 lines
1.6 KiB
Rust
47 lines
1.6 KiB
Rust
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#![allow(dead_code)]
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/// modular reduction
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///
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/// Implements automatic modular reduction in a field specified by a given relation.
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///
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/// Basically, any binary number can be written as a polynomial. This polynomial can be reduced by
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/// the relation that defines a field. In that field. This is what we call modular reduction.
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///
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/// Author: Christoph J. Scherr <software@cscherr.de>
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/// License: MIT
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/// Source: <https://git.cscherr.de/PlexSheep/plexcryptool/>
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#[test]
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fn test_modred() {
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let rel: u64 = 0x1053;
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let pol0: u64 = 0x100001;
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assert_eq!(modred(pol0, rel, false).unwrap(), 0x21e);
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}
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pub fn modred(mut poly: u64, relation: u64, verbose: bool) -> Result<u64, String> {
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let mut diffrence: u32;
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let mut index: usize = 0;
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if verbose {
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println!("relation:\t0x{:x}\t", relation);
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println!("polynomial:\t0x{:x}\t", poly);
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println!("=======================================================================");
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}
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while relation.leading_zeros() - poly.leading_zeros() != 0 {
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diffrence = relation.leading_zeros() - poly.leading_zeros();
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poly = poly ^ (relation << diffrence);
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if verbose {
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println!("{index}:\tpoly: 0x{:x}\t", poly);
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//println!("{index}:\tpoly: 0b{:b}\t", poly);
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}
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index += 1;
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}
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// one more time!
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diffrence = relation.leading_zeros() - poly.leading_zeros();
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poly = poly ^ (relation << diffrence);
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if verbose {
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println!("{index}:\tpoly: 0x{:x}\t", poly);
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//println!("{index}:\tpoly: 0b{:b}\t", poly);
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}
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return Ok(poly);
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}
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