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{-# LANGUAGE MagicHash, UnboxedTuples, NoImplicitPrelude #-}
module GHC.Integer.Logarithms
( integerLogBase#
, integerLog2#
, wordLog2#
) where
import GHC.Prim
import GHC.Integer
import qualified GHC.Integer.Logarithms.Internals as I
-- | Calculate the integer logarithm for an arbitrary base.
-- The base must be greater than 1, the second argument, the number
-- whose logarithm is sought, should be positive, otherwise the
-- result is meaningless.
--
-- > base ^ integerLogBase# base m <= m < base ^ (integerLogBase# base m + 1)
--
-- for @base > 1@ and @m > 0@.
integerLogBase# :: Integer -> Integer -> Int#
integerLogBase# b m = case step b of
(# _, e #) -> e
where
step pw =
if m `ltInteger` pw
then (# m, 0# #)
else case step (pw `timesInteger` pw) of
(# q, e #) ->
if q `ltInteger` pw
then (# q, 2# *# e #)
else (# q `quotInteger` pw, 2# *# e +# 1# #)
-- | Calculate the integer base 2 logarithm of an 'Integer'.
-- The calculation is more efficient than for the general case,
-- on platforms with 32- or 64-bit words much more efficient.
--
-- The argument must be strictly positive, that condition is /not/ checked.
integerLog2# :: Integer -> Int#
integerLog2# = I.integerLog2#
-- | This function calculates the integer base 2 logarithm of a 'Word#'.
wordLog2# :: Word# -> Int#
wordLog2# = I.wordLog2#
|
