ArrRef: Remove unnecessary copy of murmur3 hash code.

libs/arr_ref/arr_ref.nim

@@ -131,78 +131,9 @@ when defined(isNimSkull):
         if a.len != 0:
             copyMem(result[0].addr, a.arr.addr, result.len * sizeof(T))
 
-# The following is just copied straight from hashes.nim, just replacing openArray by ArrRef...
-
-when defined(js):
-  proc imul(a, b: uint32): uint32 =
-    # https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/imul
-    let mask = 0xffff'u32
-    var
-      aHi = (a shr 16) and mask
-      aLo = a and mask
-      bHi = (b shr 16) and mask
-      bLo = b and mask
-    result = (aLo * bLo) + (aHi * bLo + aLo * bHi) shl 16
-else:
-  template imul(a, b: uint32): untyped = a * b
-
-proc rotl32(x: uint32, r: int): uint32 {.inline.} =
-  (x shl r) or (x shr (32 - r))
-
 proc hash*[T](arr: ArrRef[T]): Hash =
-  # https://github.com/PeterScott/murmur3/blob/master/murmur3.c
-  const
-    c1 = 0xcc9e2d51'u32
-    c2 = 0x1b873593'u32
-    n1 = 0xe6546b64'u32
-    m1 = 0x85ebca6b'u32
-    m2 = 0xc2b2ae35'u32
-  let
-    x = arr.to byte
-    size = len(x)
-    stepSize = 4 # 32-bit
-    n = size div stepSize
-  var
-    h1: uint32
-    i = 0
-
-  # body
-  while i < n * stepSize:
-    var k1: uint32
-    when defined(js) or defined(sparc) or defined(sparc64):
-      var j = stepSize
-      while j > 0:
-        dec j
-        k1 = (k1 shl 8) or (ord(x[i+j])).uint32
-    else:
-      k1 = cast[ptr uint32](unsafeAddr x[i])[]
-    inc i, stepSize
-
-    k1 = imul(k1, c1)
-    k1 = rotl32(k1, 15)
-    k1 = imul(k1, c2)
-
-    h1 = h1 xor k1
-    h1 = rotl32(h1, 13)
-    h1 = h1*5 + n1
-
-  # tail
-  var k1: uint32
-  var rem = size mod stepSize
-  while rem > 0:
-    dec rem
-    k1 = (k1 shl 8) or (ord(x[i+rem])).uint32
-  k1 = imul(k1, c1)
-  k1 = rotl32(k1, 15)
-  k1 = imul(k1, c2)
-  h1 = h1 xor k1
-
-  # finalization
-  h1 = h1 xor size.uint32
-  h1 = h1 xor (h1 shr 16)
-  h1 = imul(h1, m1)
-  h1 = h1 xor (h1 shr 13)
-  h1 = imul(h1, m2)
-  h1 = h1 xor (h1 shr 16)
-  return cast[Hash](h1)
-
+    # Make use of stdlib's murmur3
+    # NOTE: We use the size of elements in bytes instead of the actual size
+    # just in case the actual size is bigger than that.
+    hash(cast[ptr UncheckedArray[byte]](arr.arr.addr).toOpenArray(0, arr.len * sizeof(T) - 1))
+    # TODO: for bigger elements, would a different algorithm be faster?