fix nim-lang#16542 (nim-lang#16549)

* fix nim-lang#16542

lib/pure/hashes.nim

@@ -195,10 +195,29 @@ else:
     ## Efficient hashing of integers.
     hashWangYi1(uint64(ord(x)))
 
+when defined(js):
+  proc asBigInt(x: float): int64 =
+    # result is a `BigInt` type in js, but we cheat the type system
+    # and say it is a `int64` type.
+    # TODO refactor it using bigInt once jsBigInt is ready, pending pr #1640
+    asm """
+    const buffer = new ArrayBuffer(8);
+    const floatBuffer = new Float64Array(buffer);
+    const uintBuffer = new BigUint64Array(buffer);
+    floatBuffer[0] = `x`;
+    `result` = uintBuffer[0];"""
+
 proc hash*(x: float): Hash {.inline.} =
   ## Efficient hashing of floats.
-  var y = x + 0.0 # for denormalization
-  result = hash(cast[ptr Hash](addr(y))[])
+  let y = x + 0.0 # for denormalization
+  when nimvm:
+    # workaround a JS VM bug: bug #16547
+    result = hashWangYi1(cast[int64](float64(y)))
+  else:
+    when not defined(js):
+      result = hashWangYi1(cast[Hash](y))
+    else:
+      result = hashWangYi1(asBigInt(y))
 
 # Forward declarations before methods that hash containers. This allows
 # containers to contain other containers

tests/stdlib/thashes.nim

@@ -2,7 +2,7 @@ discard """
   targets: "c cpp js"
 """
 
-import hashes
+import std/hashes
 
 block hashes:
   block hashing:
@@ -75,3 +75,32 @@ block largeSize: # longer than 4 characters
   doAssert hash(xx) == hash(ssl, 0, 4)
   doAssert hash(xx, 0, 3) == hash(xxl, 0, 3)
   doAssert hash(xx, 0, 3) == hash(ssl, 0, 3)
+
+proc main() =
+  doAssert hash(0.0) == hash(0)
+  when sizeof(int) == 8:
+    block:
+      var s: seq[Hash]
+      for a in [0.0, 1.0, -1.0, 1000.0, -1000.0]:
+        let b = hash(a)
+        doAssert b notin s
+        s.add b
+    when defined(js):
+      doAssert hash(0.345602) == 2035867618
+      doAssert hash(234567.45) == -20468103
+      doAssert hash(-9999.283456) == -43247422
+      doAssert hash(84375674.0) == 707542256
+    else:
+      doAssert hash(0.345602) == 387936373221941218
+      doAssert hash(234567.45) == -8179139172229468551
+      doAssert hash(-9999.283456) == 5876943921626224834
+      doAssert hash(84375674.0) == 1964453089107524848
+  else:
+    doAssert hash(0.345602) != 0
+    doAssert hash(234567.45) != 0
+    doAssert hash(-9999.283456) != 0
+    doAssert hash(84375674.0) != 0
+
+
+static: main()
+main()