improve barret algorithm atcoder/ac-library#163

kzrnm · kzrnm · commit 96b80b5dcd8d · 2023-05-05T14:33:06.000+09:00
diff --git a/Source/ac-library-csharp/Math/Internal/Barrett.cs b/Source/ac-library-csharp/Math/Internal/Barrett.cs
@@ -26,9 +26,8 @@ public Barrett(uint m)
         public uint Reduce(ulong z)
         {
             var x = InternalMath.Mul128Bit(z, IM);
-            var v = unchecked((uint)(z - x * Mod));
-            if (Mod <= v) v += Mod;
-            return v;
+            var y = x * Mod;
+            return (uint)(z - y + (z < y ? Mod : 0));
         }
 
         /// <summary>

Original file line number	Diff line number	Diff line change
`@@ -26,9 +26,8 @@ public Barrett(uint m)`
`26`	`26`	`public uint Reduce(ulong z)`
`27`	`27`	`{`
`28`	`28`	`var x = InternalMath.Mul128Bit(z, IM);`
`29`		`- var v = unchecked((uint)(z - x * Mod));`
`30`		`- if (Mod <= v) v += Mod;`
`31`		`- return v;`
	`29`	`+ var y = x * Mod;`
	`30`	`+ return (uint)(z - y + (z < y ? Mod : 0));`
`32`	`31`	`}`
`33`	`32`
`34`	`33`	`/// <summary>`