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#! /usr/bin/env gforth
\ Challenge 120
\
\ TASK #1 - Swap Odd/Even bits
\ Submitted by: Mohammad S Anwar
\ You are given a positive integer $N less than or equal to 255.
\
\ Write a script to swap the odd positioned bit with even positioned bit and
\ print the decimal equivalent of the new binary representation.
\
\ Example
\ Input: $N = 101
\ Output: 154
\
\ Binary representation of the given number is 01 10 01 01.
\ The new binary representation after the odd/even swap is 10 01 10 10.
\ The decimal equivalent of 10011010 is 154.
\
\ Input: $N = 18
\ Output: 33
\
\ Binary representation of the given number is 00 01 00 10.
\ The new binary representation after the odd/even swap is 00 10 00 01.
\ The decimal equivalent of 100001 is 33.
: swap_bits { n -- n }
0 0 { out shift }
BEGIN n 0> WHILE
n 1 AND IF 2 shift LSHIFT out OR TO out THEN
n 2 AND IF 1 shift LSHIFT out OR TO out THEN
n 2 RSHIFT TO n
shift 2 + TO shift
REPEAT
out ;
NEXT-ARG S>NUMBER? 0= THROW DROP
swap_bits . CR BYE
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