Refactor {Closed}Range.random

Fix FloatingPoint initialization

Precondition getting a random number from range

Author: Azoy

stdlib/public/core/FloatingPoint.swift.gyb

@@ -2112,7 +2112,7 @@ extension BinaryFloatingPoint {
     let bits = MemoryLayout<Self>.size * 8
     let fraction = bits - Self.exponentBitCount
     let random = generator.next(UInt64.self) >> (bits - fraction)
-    return Self(random) / Self(1 << fraction)
+    return Self.init(random) / Self.init(1 << fraction)
   }
 
   /*  TODO: uncomment these default implementations when it becomes possible

stdlib/public/core/Random.swift.gyb

@@ -199,6 +199,10 @@ extension Randomizable where Self: BinaryFloatingPoint {
   /// Shorthand for using the random(in:using:) function. This uses the default
   /// random implementation defined in the standard library.
   public static func random(in range: ${Range}<Self>) -> Self {
+    _precondition(
+      !range.isEmpty,
+      "Range should not be empty when getting a random number"
+    )
     return range.random!
   }
 
@@ -212,6 +216,10 @@ extension Randomizable where Self: BinaryFloatingPoint {
     in range: ${Range}<Self>,
     using generator: T
   ) -> Self {
+    _precondition(
+      !range.isEmpty,
+      "Range should not be empty when getting a random number"
+    )
     return range.random(using: generator)!
   }
 }
@@ -229,6 +237,10 @@ extension Randomizable where Self: Strideable, Self.Stride: SignedInteger {
   /// Shorthand for using the random(in:using:) function. This uses the default
   /// random implementation defined in the standard library.
   public static func random(in range: ${Range}<Self>) -> Self {
+    _precondition(
+      !range.isEmpty,
+      "Range should not be empty when getting a random number"
+    )
     return range.random!
   }
 
@@ -242,6 +254,10 @@ extension Randomizable where Self: Strideable, Self.Stride: SignedInteger {
     in range: ${Range}<Self>,
     using generator: T
   ) -> Self {
+    _precondition(
+      !range.isEmpty,
+      "Range should not be empty when getting a random number"
+    )
     return range.random(using: generator)!
   }
 }

stdlib/public/core/Range.swift.gyb

@@ -763,12 +763,11 @@ extension ${Self} where Bound: BinaryFloatingPoint {
   public func random<T: RandomNumberGenerator>(using generator: T) -> Bound? {
     guard !isEmpty else { return nil }
 %   if 'Closed' not in Self:
-    var random: Bound? =
-      Bound.random(using: generator) * abs(lowerBound - upperBound) + lowerBound
-    if random == upperBound { random = self.random(using: generator) }
-%   else:
     let random =
       Bound.random(using: generator) * abs(lowerBound - upperBound) + lowerBound
+%   else:
+    var random = Bound(generator.next(UInt64.self)) / Bound(UInt64.max)
+    random = random * abs(lowerBound - upperBound) + lowerBound
 %   end
     return random
   }