Missed optimization from #22497

grant-d · jkotas · commit 361e7dc5ee73 · 2019-02-14T18:21:52.000-08:00
diff --git a/src/System.Private.CoreLib/shared/System/Number.BigInteger.cs b/src/System.Private.CoreLib/shared/System/Number.BigInteger.cs
@@ -460,14 +460,7 @@ public static uint CountSignificantBits(uint value)
 
             public static uint CountSignificantBits(ulong value)
             {
-                uint upper = (uint)(value >> 32);
-
-                if (upper != 0)
-                {
-                    return 32 + CountSignificantBits(upper);
-                }
-
-                return CountSignificantBits((uint)value);
+                return 64 - (uint)BitOps.LeadingZeroCount(value);
             }
 
             public static uint CountSignificantBits(ref BigInteger value)

Original file line number	Diff line number	Diff line change
`@@ -460,14 +460,7 @@ public static uint CountSignificantBits(uint value)`
`460`	`460`
`461`	`461`	`public static uint CountSignificantBits(ulong value)`
`462`	`462`	`{`
`463`		`- uint upper = (uint)(value >> 32);`
`464`		`-`
`465`		`- if (upper != 0)`
`466`		`- {`
`467`		`- return 32 + CountSignificantBits(upper);`
`468`		`- }`
`469`		`-`
`470`		`- return CountSignificantBits((uint)value);`
	`463`	`+ return 64 - (uint)BitOps.LeadingZeroCount(value);`
`471`	`464`	`}`
`472`	`465`
`473`	`466`	`public static uint CountSignificantBits(ref BigInteger value)`