initial DDMath implementation

2026-09-14 22:25:50 +04:00
parent 4efecbb1bc
commit beb9a084d0
4 changed files with 281 additions and 4 deletions
@@ -0,0 +1,35 @@
+using Shouldly;
+using Xunit;
+
+namespace Just.PreciseMath.Tests;
+
+public class PreciseMathTests
+{
+    [Fact]
+    public void AbsPreservesBothComponentsAndCanonicalSpecialValues()
+    {
+        double[] scalars = [0.0, -0.0, 1.0, -1.0, double.Epsilon, -double.Epsilon,
+            double.MaxValue, double.MinValue, double.PositiveInfinity, double.NegativeInfinity, double.NaN];
+        foreach (double scalar in scalars)
+        {
+            // Binary64 is an independent reference when the input has no residual.
+            DoubleDouble actual = DDMath.Abs(new DoubleDouble(scalar));
+            AssertBits(actual, double.IsNaN(scalar) ? double.NaN : Math.Abs(scalar), 0.0);
+            DoubleDouble.IsCanonical(actual).ShouldBeTrue();
+        }
+
+        foreach (double low in new[] { Math.ScaleB(1.0, -54), -Math.ScaleB(1.0, -54), double.Epsilon, -double.Epsilon })
+        {
+            DoubleDouble positive = DoubleDouble.FromComponents(1.0, low);
+            DoubleDouble negative = DoubleDouble.FromComponents(-1.0, -low);
+            AssertBits(DDMath.Abs(positive), 1.0, low);
+            AssertBits(DDMath.Abs(negative), 1.0, low);
+        }
+    }
+
+    private static void AssertBits(DoubleDouble actual, double high, double low)
+    {
+        BitConverter.DoubleToInt64Bits(actual.High).ShouldBe(BitConverter.DoubleToInt64Bits(high));
+        BitConverter.DoubleToInt64Bits(actual.Low).ShouldBe(BitConverter.DoubleToInt64Bits(low));
+    }
+}