Merge 3dc39fe into b5de583

Author: idavis

library/std/src/Std/OpenQASM/Angle.qs

@@ -85,6 +85,13 @@ function DoubleAsAngle(value : Double, size : Int) : Angle {
         value = value + tau;
     }
 
+    // Handle the edge case where modulo returns tau due to floating-point precision
+    // we've seen this when the user rotates by f64::EPSILON / 2.0 causing the value
+    // to be still equal to tau after the modulo operation.
+    if value >= tau {
+        value = 0.;
+    }
+
     Std.Diagnostics.Fact(value >= 0., "Value must be >= 0.");
     Std.Diagnostics.Fact(value < tau, "Value must be < tau.");
     Std.Diagnostics.Fact(size > 0, "Size must be > 0");

source/compiler/qsc_qasm/src/stdlib/angle.rs

@@ -52,6 +52,17 @@ impl Angle {
             val += TAU;
         }
 
+        // Handle the edge case where modulo returns tau due to floating-point precision
+        // we've seen this when the user rotates by f64::EPSILON / 2.0 causing the value
+        // to be still equal to tau after the modulo operation.
+        if val >= TAU {
+            val = 0.;
+        }
+
+        assert!(val >= 0., "Value must be >= 0.");
+        assert!(val < TAU, "Value must be < tau.");
+        assert!(size > 0, "Size must be > 0");
+
         // If the size is > f64::MANTISSA_DIGITS, the cast to f64
         // on the next lines will loose precission.
         if size > f64::MANTISSA_DIGITS {

source/compiler/qsc_qasm/src/stdlib/angle/tests.rs

@@ -5,6 +5,7 @@
 #![allow(clippy::unreadable_literal)]
 
 use std::convert::TryInto;
+use std::f64;
 use std::f64::consts::{PI, TAU};
 
 use super::Angle;
@@ -269,3 +270,12 @@ fn test_angle_cast_truncation() {
     assert_eq!(new_angle.value, 0b1010);
     assert_eq!(new_angle.size, 4);
 }
+
+#[test]
+fn test_angle_off_by_less_than_epsilon_from_tau_maintains_invariants() {
+    // testing (-f64::EPSILON / 2.0) % f64::EPSILON + f64::EPSILON equals f64::EPSILON
+    // we need to ensure that the angle is still in the range [0, TAU)
+    let angle = Angle::from_f64_maybe_sized(-f64::EPSILON / 2.0, None);
+    assert_eq!(angle.value, 0);
+    assert!(angle.size == 53);
+}