Make FloatingPoint.random exclusive

Author: Azoy

stdlib/public/core/FloatingPoint.swift.gyb

@@ -2106,11 +2106,13 @@ extension BinaryFloatingPoint {
   /// - Returns: A random representation of this floating point conforming to
   ///   `Randomizable`
   ///
-  /// The range of this random floating point is from 0 to 1 inclusive
+  /// The range of this random floating point is from 0 to 1 exclusive
   @_inlineable
   public static func random<T: RandomNumberGenerator>(using generator: T) -> Self {
-    let random = generator.next(UInt64.self)
-    return Self(random) / Self(UInt64.max)
+    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)
   }
 
   /*  TODO: uncomment these default implementations when it becomes possible