init

src/uniformity/chi_byte.rs

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+use std::collections::HashMap;
+use statrs::distribution::{ChiSquared, ContinuousCDF};
+
+use crate::Onod;
+
+impl Onod {
+
+    /// ChiByte randomness test
+    /// Evaluates the uniformity of byte values across the data and returns a p-value.
+    pub fn chi_byte(samples: &[u8]) -> f64 {
+
+        if samples.is_empty() {
+            return 0.0; // Default to perfect randomness for empty data
+        }
+
+        // Count occurrences of each byte value (0-255)
+        let mut counts = HashMap::new();
+        for &byte in samples {
+            *counts.entry(byte).or_insert(0) += 1;
+        }
+
+        // Calculate expected count assuming uniform distribution
+        let expected_count = samples.len() as f64 / 256.0;
+
+        // Calculate chi-squared statistic
+        let mut chi_squared_stat = 0.0;
+        for i in 0..256 {
+            let observed = *counts.get(&(i as u8)).unwrap_or(&0) as f64;
+            let diff = observed - expected_count;
+            chi_squared_stat += (diff * diff) / expected_count;
+        }
+
+        // Use chi-squared distribution to calculate p-value
+        let degrees_of_freedom = 256.0 - 1.0; // 256 possible byte values - 1
+        let chi_squared_dist = ChiSquared::new(degrees_of_freedom).expect("Failed to create ChiSquared distribution");
+        let p_value = 1.0 - chi_squared_dist.cdf(chi_squared_stat);
+
+        p_value
+    }
+
+}