add CCFloat.{fsign, sign_exn}

core/CCFloat.ml

@@ -76,6 +76,17 @@ let sign (a:float) =
   else if a > 0.0 then 1 
   else 0
 
+let fsign a =
+  if is_nan a then nan
+  else if a = 0. then a
+  else Pervasives.copysign 1. a
+
+exception TrapNaN of string
+
+let sign_exn (a:float) =
+  if is_nan a then raise (TrapNaN "sign")
+  else compare a 0.
+
 let to_int (a:float) = Pervasives.int_of_float a
 let of_int (a:int) = Pervasives.float_of_int a
 

core/CCFloat.mli

@@ -77,7 +77,20 @@ val random_small : t random_gen
 val random_range : t -> t -> t random_gen
 
 val sign : t -> int
-(** [sign t] is one of [-1, 0, 1] *)
+(** [sign t] is one of [-1, 0, 1], depending on how the float
+    compares to [0.]
+    @deprecated use {! fsign} or {!sign_exn} since it's more accurate *)
+
+val fsign : t -> float
+(** [fsign x] is one of [-1., -0., +0., +1.], or [nan] if [x] is NaN.
+    @since NEXT_RELEASE *)
+
+exception TrapNaN of string
+val sign_exn : t -> int
+(** [sign_exn x] will return the sign of [x] as [1, 0] or [-1], or raise an
+    exception [TrapNaN] if [x] is a NaN.
+    Note that infinities have defined signs in OCaml.
+    @since NEXT_RELEASE *)
 
 val to_int : t -> int
 val of_int : int -> t