[Standard library] Break up another “large” expression.

DougGregor · DougGregor · commit ee1713ce673e · 2018-07-27T15:37:59.000-07:00
Bitwise arithmetic is a killer for the type checker :(. Shave off another
half second of typecheck time in the standard library.
diff --git a/stdlib/public/core/UTF16.swift b/stdlib/public/core/UTF16.swift
@@ -60,7 +60,9 @@ extension Unicode.UTF16 : Unicode.Encoding {
       return Unicode.Scalar(_unchecked: bits & 0xffff)
     }
     _sanityCheck(source._bitCount == 32)
-    let value = 0x10000 + (bits >> 16 & 0x03ff | (bits & 0x03ff) << 10)
+    let lower: UInt32 = bits >> 16 & 0x03ff
+    let upper: UInt32 = (bits & 0x03ff) << 10
+    let value = 0x10000 + (lower | upper)
     return Unicode.Scalar(_unchecked: value)
   }
 

Original file line number	Diff line number	Diff line change
`@@ -60,7 +60,9 @@ extension Unicode.UTF16 : Unicode.Encoding {`
`60`	`60`	`return Unicode.Scalar(_unchecked: bits & 0xffff)`
`61`	`61`	`}`
`62`	`62`	`_sanityCheck(source._bitCount == 32)`
`63`		`- let value = 0x10000 + (bits >> 16 & 0x03ff \| (bits & 0x03ff) << 10)`
	`63`	`+ let lower: UInt32 = bits >> 16 & 0x03ff`
	`64`	`+ let upper: UInt32 = (bits & 0x03ff) << 10`
	`65`	`+ let value = 0x10000 + (lower \| upper)`
`64`	`66`	`return Unicode.Scalar(_unchecked: value)`
`65`	`67`	`}`
`66`	`68`