Ethiopian multiplication: Difference between revisions

=={{header|REXX}}==

<lang rexx>

/*REXX program multiplies 2 integers by Ethiopian/Russian peasant method*/

numeric digits 1000 /*handle extremely large integers. */

parse arg a b . /*handles zeroes and negative integers.*/

/*A & B should be checked if integers.*/

say 'a=' a

say 'b=' b

say 'product=' emult(a,b)

exit

emult: procedure; parse arg x 1 ox,y

prod=0

do while x\==0

if \iseven(x) then prod=prod+y

x=halve(x)

y=double(y)

end

return prod*sign(ox)

halve: return arg(1)%2

double: return arg(1)*2

iseven: return arg(1)//2==0

/*Note: the above procedures don't modify (or define) any */

/*local variables, so there is no need to specify PROCEDURE */

/*REXX allows multiple definitions, only the 1st one is used. */

/*Three different argument names (methodologies?) are shown. */

halve: procedure; parse arg ?; return ?%2

double: procedure; parse arg x; return x+x

iseven: procedure; parse arg _; return _//2 == 0

</lang>