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davejachimiak/sicp1.17.hs

Created October 25, 2014 19:24
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sicp 1.17 in haskell
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sicp1.17.hs
-- ...
-- ...
-- [Assume your language doesn't have a multiplication function or
-- table. Given `double` and `half` functions,] design a
-- multiplication procedure that uses a logarithmic number of steps.
double :: Integer -> Integer
double x = x + x
halve :: Integer -> Integer
halve x = x `div` 2
m :: Integer -> Integer -> Integer
m x y
| y == 0 = 0
| odd y = x + m x (y - 1)
| otherwise = m (double x) (halve y)
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