fix: PI format for rust Circuit display

crates/circuit/src/circuit_drawer.rs

@@ -60,7 +60,7 @@ pub fn draw_circuit(
             if approx::abs_diff_eq!(*f, 0.) {
                 String::new()
             } else {
-                format!("global phase: {}\n", f)
+                format!("global phase: {}\n", format_float_pi(*f))
             }
         }
         Param::ParameterExpression(expr) => {
@@ -763,7 +763,7 @@ impl TextDrawer {
                         .params_view()
                         .iter()
                         .map(|param| match param {
-                            Param::Float(f) => f.to_string(),
+                            Param::Float(f) => format_float_pi(*f),
                             Param::ParameterExpression(expr) => expr.to_string(),
                             _ => format!("{:?}", param),
                         })
@@ -1202,6 +1202,42 @@ impl TextDrawer {
     }
 }
 
+fn format_float_pi(f: f64) -> String {
+    const DELTA: f64 = 1e-9; // This is the minimal treshold to accept a number as pi 
+    const DENOMINATOR: i64 = 16; // This is the max denominator used to find ratio. 16 is used here but greater or smaller values could be added for either precison or speed
+
+    if approx::abs_diff_eq!(f, 0.0, epsilon = DELTA) {
+        return "0".to_string();
+    }
+
+    let frac: f64 = f / std::f64::consts::PI;
+
+    for q in 1..DENOMINATOR {
+        let p: i64 = (frac * q as f64).round() as i64;
+
+        if p == 0 {
+            continue;
+        }
+
+        if approx::abs_diff_eq!(p as f64 / q as f64, frac, epsilon = DELTA) {
+            let sign = match p {
+                x if x < 0 => "-",
+                _ => "",
+            };
+            let numerator = p.unsigned_abs();
+
+            return match (numerator, q) {
+                (1, 1) => format!("{}π", sign),
+                (n, 1) => format!("{}{}π", sign, n),
+                (1, d) => format!("{}π/{}", sign, d),
+                (n, d) => format!("{}{}π/{}", sign, n, d),
+            };
+        }
+    }
+
+    f.to_string() // case no denominator found
+}
+
 #[cfg(test)]
 mod tests {
     use ndarray::Array2;
@@ -1902,4 +1938,24 @@ q_1: ┤ Ry(🎩) ├┤1          ├┤ 💶🔉(🎩) ├┤1           ├
 ";
         assert_eq!(result, expected.trim_start_matches("\n"));
     }
+
+    #[test]
+    fn test_pi_float_format() {
+        use std::f64::consts::PI;
+
+        assert_eq!(format_float_pi(0.0), "0");
+        assert_eq!(format_float_pi(PI), "π");
+        assert_eq!(format_float_pi(2.0 * PI), "2π");
+        assert_eq!(format_float_pi(1.0 * PI), "π");
+        assert_eq!(format_float_pi(PI / 3.0), "π/3");
+        assert_eq!(format_float_pi(2.0 * PI / 3.0), "2π/3");
+        assert_eq!(format_float_pi(-PI), "-π");
+        assert_eq!(format_float_pi(-PI / 4.0), "-π/4");
+        assert_eq!(format_float_pi(5.0), "5");
+        assert_eq!(format_float_pi(PI / 15.0), "π/15");
+
+        let x = PI / 17.0;
+        assert_eq!(format_float_pi(PI / 17.0), x.to_string());
+        assert_eq!(format_float_pi(3.14159), "3.14159");
+    }
 }