Clamp Number-to-Int functions

src/Data/Int.erl

@@ -1,10 +1,12 @@
 -module(data_int@foreign).
 -export([fromNumberImpl/3,toNumber/1,fromStringAsImpl/4,toStringAs/2,pow/2,quot/2,'rem'/2]).
 
-fromNumberImpl(Just, Nothing, N) ->
-  case trunc(N) of
-    N1 when N1 == N -> Just(N1);
-    _ -> Nothing
+fromNumberImpl(Just, Nothing, N) when is_float(N) ->
+  %% this uses only float ops that should be trivial and exact
+  Abs = abs(N),
+  AbsFloor = math:floor(Abs),
+  if AbsFloor =:= Abs, Abs =< 9.007199254740991e15 -> Just(trunc(N));
+     true -> Nothing
   end.
 
 toNumber(N) -> float(N).
@@ -18,4 +20,4 @@ pow(X,Y) -> trunc(math:pow(X,Y)).
 
 quot(X, Y) -> X div Y.
 
-'rem'(X, Y) -> X rem Y.
+'rem'(X, Y) -> X rem Y.

src/Data/Int.purs

@@ -60,10 +60,14 @@ ceil = unsafeClamp <<< Math.ceil
 round :: Number -> Int
 round = unsafeClamp <<< Math.round
 
--- | Convert an integral `Number` to an `Int`, by clamping to the `Int` range.
--- | This function will return 0 if the input is `NaN` or an `Infinity`.
+-- | Convert an integral `Number` to an `Int`, by clamping to the range of
+-- | integers which have an exact representation as floats. This function
+-- | will return 0 if the input is `NaN` or an `Infinity`.
 unsafeClamp :: Number -> Int
-unsafeClamp x = fromMaybe 0 (fromNumber x)
+unsafeClamp x
+  | x >= 9007199254740991.0 = 9007199254740991
+  | x <= -9007199254740991.0 = -9007199254740991
+  | otherwise = fromMaybe 0 (fromNumber x)
 
 -- | Converts an `Int` value back into a `Number`. Any `Int` is a valid `Number`
 -- | so there is no loss of precision with this function.

test/Test/Data/Int.purs

@@ -38,18 +38,19 @@ testInt = do
   assert $ floor 0.3 == 0
   assert $ floor 0.7 == 0
 
-  -- log "round, ceil, and floor should clamp values outside the Int range"
-  -- let testClamping f = do
-  --       let low = toNumber bottom - 1.5
-  --       assert $ f low == bottom
-  --
-  --       let high = toNumber top + 1.5
-  --       assert $ f high == top
-
-  -- testClamping round
-  -- testClamping ceil
-  -- testClamping floor
-
+  log "round, ceil, and floor should clamp values outside the exact range"
+  let testClamping f = do
+        let bottom = -9007199254740991
+        let low = toNumber bottom - 1.5
+        assert $ f low == bottom
+
+        let top = 9007199254740991
+        let high = toNumber top + 1.5
+        assert $ f high == top
+
+  testClamping round
+  testClamping ceil
+  testClamping floor
 
   -- log "round, ceil, and floor should return 0 for NaN and Infinities"
   -- let testNonNumber f = do