simplify code for handling float 0/-0

Author: timotheecour

lib/pure/hashes.nim

@@ -118,13 +118,7 @@ proc hash*[T: SomeNumber | Ordinal | char](x: T): Hash {.inline.} =
       # bugfix: the previous code was using `x = x + 1.0` (presumably for
       # handling negative 0), however this leads to collisions for small x due
       # to FP finite precision.
-      let x: BiggestInt =
-        if x == 0: 0.BiggestInt
-        else:
-          when sizeof(BiggestInt) == sizeof(T):
-            cast[BiggestInt](x)
-          else: # for nimvm
-            cast[int32](x).BiggestInt
+      let x = cast[BiggestInt](x + T(0))
     else:
       let x = x.BiggestInt
     hashBiggestInt(x)

tests/stdlib/thashes.nim

@@ -15,3 +15,10 @@ suite "hashes":
     test "0.0 and -0.0 should have the same hash value":
       var dummy = 0.0
       check hash(dummy) == hash(-dummy)
+      check hash(0.0) == hash(-0.0)
+      check hash(0.0f) == hash(-0.0f)
+      let h1 = hash(0.0)
+      const h2 = hash(0.0)
+      const h3 = hash(-0.0)
+      check h1 == h2
+      check h1 == h3