fb-util-0.1.0.1: Util/Bits.hs

{-
  Copyright (c) Meta Platforms, Inc. and affiliates.
  All rights reserved.

  This source code is licensed under the BSD-style license found in the
  LICENSE file in the root directory of this source tree.
-}

{-# LANGUAGE MagicHash #-}
module Util.Bits (bitLength) where

import GHC.Exts
import GHC.Integer.Logarithms

-- | The number of bits in the minimal two's-complement
-- representation, excluding a sign bit.
--
-- > bitLength 3 = 2
-- > bitLength 4 = 3
--
-- See http://mathworld.wolfram.com/BitLength.html for more information.
bitLength :: Integral a => a -> Int
bitLength = integerBitLength . toInteger
  where
  integerBitLength n
    | n < 0 = integerBitLength $ -1 - n
    | n == 0 = 0
    | otherwise = I# (1# +# integerLog2# n)