RootSample - divide out factors of 4

brian-dot-net · Aug 27, 2018 · 69c7763 · 69c7763
1 parent c106472
commit 69c7763
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Showing 2 changed files with 68 additions and 3 deletions.
diff --git a/projects/RootSample/RootSample.Core/RootTerm.cs b/projects/RootSample/RootSample.Core/RootTerm.cs
@@ -5,16 +5,71 @@
 namespace RootSample
 {
     using System;
+    using System.Text;
 
     public struct RootTerm
     {
-        private readonly int n;
+        private readonly int c;
+        private readonly int x;
 
         public RootTerm(int n)
         {
-            this.n = (int)Math.Sqrt(n);
+            if (n == 0)
+            {
+                this.c = 0;
+                this.x = 0;
+            }
+            else
+            {
+                this.c = 1;
+                while (true)
+                {
+                    int r;
+                    int m = Math.DivRem(n, 4, out r);
+                    if (r != 0)
+                    {
+                        break;
+                    }
+
+                    n = m;
+                    this.c *= 2;
+                }
+
+                int s = (int)Math.Sqrt(n);
+                if (s * s == n)
+                {
+                    this.x = 1;
+                    this.c *= s;
+                }
+                else
+                {
+                    this.x = n;
+                }
+            }
         }
 
-        public override string ToString() => this.n.ToString();
+        public override string ToString()
+        {
+            StringBuilder sb = new StringBuilder();
+            if (this.c != 1)
+            {
+                sb.Append(this.c);
+            }
+
+            if (this.x > 1)
+            {
+                sb.Append('*');
+                sb.Append("sqrt(");
+                sb.Append(this.x);
+                sb.Append(')');
+            }
+
+            if (sb.Length == 0)
+            {
+                return "1";
+            }
+
+            return sb.ToString();
+        }
     }
 }
diff --git a/projects/RootSample/RootSample.Test/RootTermTest.cs b/projects/RootSample/RootSample.Test/RootTermTest.cs
@@ -21,5 +21,15 @@ public void PerfectSquares(int n, string expected)
         {
             new RootTerm(n).ToString().Should().Be(expected, "sqrt({0}) is {1}", n, expected);
         }
+
+        [Theory]
+        [InlineData(8, "2*sqrt(2)")]
+        [InlineData(24, "2*sqrt(6)")]
+        [InlineData(262084, "2*sqrt(65521)")]
+        [InlineData(2147483644, "2*sqrt(536870911)")]
+        public void FactorsOfFour(int n, string expected)
+        {
+            new RootTerm(n).ToString().Should().Be(expected, "sqrt({0}) is {1}", n, expected);
+        }
     }
 }