[stdlib] Fix bug in Bit with-overflow arithmetic

PatrickPijnappel · PatrickPijnappel · commit 9f162728f199 · 2015-12-20T17:21:13.000+11:00
The original version would result in a crash for negative results.
diff --git a/stdlib/public/core/Bit.swift b/stdlib/public/core/Bit.swift
@@ -98,7 +98,8 @@ extension Bit : IntegerArithmeticType {
     if let b = Bit(rawValue: v.0) {
       return (b, v.overflow)
     } else {
-      return (Bit(rawValue: v.0 % 2)!, true)
+      let bitRaw = v.0 > 0 ? v.0 % 2 : v.0 % 2 + 2
+      return (Bit(rawValue: bitRaw)!, true)
     }
   }
 

Original file line number	Diff line number	Diff line change
`@@ -98,7 +98,8 @@ extension Bit : IntegerArithmeticType {`
`98`	`98`	`if let b = Bit(rawValue: v.0) {`
`99`	`99`	`return (b, v.overflow)`
`100`	`100`	`} else {`
`101`		`- return (Bit(rawValue: v.0 % 2)!, true)`
	`101`	`+ let bitRaw = v.0 > 0 ? v.0 % 2 : v.0 % 2 + 2`
	`102`	`+ return (Bit(rawValue: bitRaw)!, true)`
`102`	`103`	`}`
`103`	`104`	`}`
`104`	`105`