In section 4.3.3, the algorithm for the division of a signed
binary stream by an integer was defined as follows:
The Haskell implementation of this algorithm is as follows:
-- sbIntDiv : Division of a signed binary stream by an integer sbIntDiv :: SBinStream -> Int -> SBinStream sbIntDiv _ 0 = undefined sbIntDiv x 1 = x sbIntDiv x (-1) = sbNegate x sbIntDiv x n = sbIntDiv' x n 0 -- sbIntDiv' : Auxiliary to sbIntDiv sbIntDiv' :: SBinStream -> Int -> Int -> SBinStream sbIntDiv' (a:x) n s = if (s' >= n) then ( 1:sbIntDiv' x n (s'-n)) else if (s' <= -n) then ( -1:sbIntDiv' x n (s'+n)) else ( 0:sbIntDiv' x n s') where s' = 2*s+a
The algorithm and implementation are essentially the same. The only changes required are syntactic.
The lines starting with a double minus signed (
comments. The lines starting with a function name and followed by a
double colon (
::) are type definitions, and the remaining lines
are the function definitions. The first three cases for
sbIntDiv catch division by zero and avoid trivial divisions by
one or minus one. The keyword
where is a kind of postfix
version of ML's
let ... in ... statement. It allows us to
define variables which are used in the main expression, and makes the
code extremely readable.
The only remaining differences are that `cons' is represented using a single colon rather than the double one used in the algorithm description, and the three cases in the algorithm description are implemented using an if then statement.