Add cmpf to float.mc

stdlib/float.mc

@@ -51,3 +51,28 @@ utest absf 1. with 1. using eqf
 utest absf -1. with 1. using eqf
 utest absf -0. with 0. using eqf
 utest isNaN (absf nan) with true
+
+
+-- `cmpf l r` compares `l` and `r`. `cmpf l r = -1` if l < r, `cmpf l r = 1` if
+-- l > r, and `cmpf l r = 0` if l = r. `nan` is considered smaller than negative
+-- infinity and equal to itself.
+let cmpf: Float -> Float -> Int = lam l. lam r.
+  let lIsNaN = isNaN l in
+  let rIsNaN = isNaN r in
+  if and lIsNaN rIsNaN then 0
+  else if lIsNaN then -1
+  else if rIsNaN then 1
+  else
+    if ltf l r then -1 else if gtf l r then 1 else 0
+
+utest cmpf 0. 0. with 0
+utest cmpf 1. 0. with 1
+utest cmpf 0. 1. with -1
+utest cmpf inf inf with 0
+utest cmpf (negf inf) (negf inf) with 0
+utest cmpf inf inf with 0
+utest cmpf (negf inf) 0. with -1
+utest cmpf 0. (negf inf) with 1
+utest cmpf nan nan with 0
+utest cmpf nan (negf inf) with -1
+utest cmpf (negf inf) nan with 1