Run next() for uninitialized Random values (#2321)

The current implementations of XorOshiro128Plus and XorShift128Plus return the sum of input seed values for the first value, which is unsafe. Rather than telling people to discard the first value, skip past it in the actual implementation. This commit also fixes the documentation of current implementations for consistency with the Random trait. Resolves #2320
ponylang · Nov 16, 2017 · 0785ebd · 0785ebd
1 parent 981b472
commit 0785ebd
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Showing 3 changed files with 5 additions and 3 deletions.
diff --git a/packages/random/mt.pony b/packages/random/mt.pony
@@ -28,7 +28,7 @@ class MT is Random
 
   fun ref next(): U64 =>
     """
-    A random integer in [0, 2^64 - 1]
+    A random integer in [0, 2^64)
     """
     if _index >= _n() then
       _populate()

diff --git a/packages/random/xoroshiro.pony b/packages/random/xoroshiro.pony
@@ -16,10 +16,11 @@ class XorOshiro128Plus is Random
     """
     _x = x
     _y = y
+    next()
 
   fun ref next(): U64 =>
     """
-    A random integer in [0, 2^64 - 1]
+    A random integer in [0, 2^64)
     """
     let x = _x
     var y = _y

diff --git a/packages/random/xorshift.pony b/packages/random/xorshift.pony
@@ -17,10 +17,11 @@ class XorShift128Plus is Random
     """
     _x = x
     _y = y
+    next()
 
   fun ref next(): U64 =>
     """
-    A random integer in [0, 2^64 - 1]
+    A random integer in [0, 2^64)
     """
     var y = _x
     let x = _y