Created
April 20, 2013 12:49
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Loop-unrolled Ackermann function.
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-- See http://stackoverflow.com/q/16115815/242169 | |
-- Run with +RTS -kc1M to avoid space leak | |
-- | |
-- Test: | |
-- $ time ./Test +RTS -kc1M | |
-- 65533 | |
-- ./Test +RTS -kc1M 6,30s user 0,04s system 97% cpu 6,516 total | |
--- | |
{-# LANGUAGE CPP #-} | |
module Main where | |
data P = P {-# UNPACK #-} !Int {-# UNPACK #-} !Int | |
ack0 :: Int -> Int | |
ack0 n =(n+1) | |
#define C(a) a | |
#define CONCAT(a,b) C(a)C(b) | |
#define AckType(M) CONCAT(ack,M) :: Int -> Int | |
AckType(1) | |
AckType(2) | |
AckType(3) | |
AckType(4) | |
#define AckDecl(M,M1) \ | |
CONCAT(ack,M) n = case n of { 0 -> CONCAT(ack,M1) 1 \ | |
; 1 -> CONCAT(ack,M1) (CONCAT(ack,M1) 1) \ | |
; _ -> CONCAT(ack,M1) (CONCAT(ack,M) (n-1)) } | |
AckDecl(1,0) | |
AckDecl(2,1) | |
AckDecl(3,2) | |
AckDecl(4,3) | |
ack :: P -> (Int -> Int) -> Int | |
ack (P m n) k = case m of | |
0 -> k (ack0 n) | |
1 -> k (ack1 n) | |
2 -> k (ack2 n) | |
3 -> k (ack3 n) | |
4 -> k (ack4 n) | |
_ -> case n of | |
0 -> ack (P (m-1) 1) k | |
1 -> ack (P (m-1) 1) (\a -> ack (P (m-1) a) k) | |
_ -> ack (P m (n-1)) (\a -> ack (P (m-1) a) k) | |
main :: IO () | |
main = print $ ack (P 4 1) id |
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