ARM64 intrinsic for TrailingZeroCount

kunalspathak · kunalspathak · commit a2effc731283 · 2020-04-02T22:57:44.000-07:00
diff --git a/src/libraries/System.Private.CoreLib/src/System/Numerics/BitOperations.cs b/src/libraries/System.Private.CoreLib/src/System/Numerics/BitOperations.cs
@@ -296,6 +296,11 @@ public static int TrailingZeroCount(uint value)
                 return (int)Bmi1.TrailingZeroCount(value);
             }
 
+            if (ArmBase.IsSupported)
+            {
+                return (int)ArmBase.LeadingZeroCount(ArmBase.ReverseElementBits(value));
+            }
+
             // Unguarded fallback contract is 0->0
             if (value == 0)
             {
@@ -334,6 +339,10 @@ public static int TrailingZeroCount(ulong value)
                 return (int)Bmi1.X64.TrailingZeroCount(value);
             }
 
+            if (ArmBase.Arm64.IsSupported)
+            {
+                return (int)ArmBase.Arm64.LeadingZeroCount(ArmBase.Arm64.ReverseElementBits(value));
+            }
             uint lo = (uint)value;
 
             if (lo == 0)

Original file line number	Diff line number	Diff line change
`@@ -296,6 +296,11 @@ public static int TrailingZeroCount(uint value)`
`296`	`296`	`return (int)Bmi1.TrailingZeroCount(value);`
`297`	`297`	`}`
`298`	`298`
	`299`	`+ if (ArmBase.IsSupported)`
	`300`	`+ {`
	`301`	`+ return (int)ArmBase.LeadingZeroCount(ArmBase.ReverseElementBits(value));`
	`302`	`+ }`
	`303`	`+`
`299`	`304`	`// Unguarded fallback contract is 0->0`
`300`	`305`	`if (value == 0)`
`301`	`306`	`{`
`@@ -334,6 +339,10 @@ public static int TrailingZeroCount(ulong value)`
`334`	`339`	`return (int)Bmi1.X64.TrailingZeroCount(value);`
`335`	`340`	`}`
`336`	`341`
	`342`	`+ if (ArmBase.Arm64.IsSupported)`
	`343`	`+ {`
	`344`	`+ return (int)ArmBase.Arm64.LeadingZeroCount(ArmBase.Arm64.ReverseElementBits(value));`
	`345`	`+ }`
`337`	`346`	`uint lo = (uint)value;`
`338`	`347`
`339`	`348`	`if (lo == 0)`