44 lines
1.2 KiB
Rust
44 lines
1.2 KiB
Rust
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use statrs::distribution::{Normal, ContinuousCDF};
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use crate::Onod;
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impl Onod {
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/// Entropy randomness test
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/// Calculates the Shannon entropy of a byte slice and outputs a p-value.
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pub fn shannon(samples: &[u8]) -> f64 {
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let len = samples.len() as f64;
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if len == 0.0 {
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return 0.0;
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}
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// Count occurrences of each byte
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let mut counts = [0usize; 256];
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for &byte in samples {
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counts[byte as usize] += 1;
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}
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// Calculate Shannon entropy
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let entropy: f64 = counts.iter()
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.filter(|&&count| count > 0)
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.map(|&count| {
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let p = count as f64 / len;
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-p * p.log2()
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})
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.sum();
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// Expected entropy for a uniform distribution
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let expected_entropy = 8.0;
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// Calculate Z statistic
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let std_dev = (0.833_f64).sqrt();
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let z_score = (entropy - expected_entropy) * len.sqrt() / std_dev;
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// Calculate p-value from Z score
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let normal_dist = Normal::new(0.0, 1.0).expect("Failed to create Normal distribution");
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let p_value = 2.0 * (1.0 - normal_dist.cdf(z_score.abs())); // Two-tailed test
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p_value
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}
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}
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