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{-# LANGUAGE Trustworthy #-}
{-# LANGUAGE CPP, MagicHash, UnboxedTuples, NoImplicitPrelude #-}
{-# OPTIONS_GHC -O2 #-}
{-# OPTIONS_HADDOCK not-home #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Float.ConversionUtils
-- Copyright : (c) Daniel Fischer 2010
-- License : see libraries/base/LICENSE
--
-- Maintainer : cvs-ghc@haskell.org
-- Stability : internal
-- Portability : non-portable (GHC Extensions)
--
-- Utilities for conversion between Double/Float and Rational
--
-----------------------------------------------------------------------------
#include "MachDeps.h"
module GHC.Float.ConversionUtils ( elimZerosInteger, elimZerosInt# ) where
import GHC.Base
import GHC.Num.Integer
default ()
#if WORD_SIZE_IN_BITS < 64
#define TO64 integerToInt64#
-- Double mantissae have 53 bits, too much for Int#
elim64# :: Int64# -> Int# -> (# Integer, Int# #)
elim64# n e =
case zeroCount (int64ToInt# n) of
t | isTrue# (e <=# t) -> (# integerFromInt64# (uncheckedIShiftRA64# n e), 0# #)
| isTrue# (t <# 8#) -> (# integerFromInt64# (uncheckedIShiftRA64# n t), e -# t #)
| otherwise -> elim64# (uncheckedIShiftRA64# n 8#) (e -# 8#)
#else
#define TO64 integerToInt#
-- Double mantissae fit it Int#
elim64# :: Int# -> Int# -> (# Integer, Int# #)
elim64# = elimZerosInt#
#endif
{-# INLINE elimZerosInteger #-}
elimZerosInteger :: Integer -> Int# -> (# Integer, Int# #)
elimZerosInteger m e = elim64# (TO64 m) e
elimZerosInt# :: Int# -> Int# -> (# Integer, Int# #)
elimZerosInt# n e =
case zeroCount n of
t | isTrue# (e <=# t) -> (# IS (uncheckedIShiftRA# n e), 0# #)
| isTrue# (t <# 8#) -> (# IS (uncheckedIShiftRA# n t), e -# t #)
| otherwise -> elimZerosInt# (uncheckedIShiftRA# n 8#) (e -# 8#)
-- | Number of trailing zero bits in a byte
zeroCount :: Int# -> Int#
zeroCount i = int8ToInt# (indexInt8OffAddr# arr (word2Int# (narrow8Word# (int2Word# i)))) -- index must be in [0,255]
where
arr = "\8\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\5\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\6\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\5\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\7\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\5\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\6\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\5\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0\4\0\1\0\2\0\1\0\3\0\1\0\2\0\1\0"#
|
