A recent query on comp.lang.tcl asked how one might find the sum of two binary numbers, without converting them to decimal returning the result as binary.
Glen Jackson wrote the following code:
if {[string match 8.4* [package require Tcl]]} {
package require struct::list
interp alias {} list_reverse {} struct::list reverse
} else {
interp alias {} list_reverse {} lreverse
}
proc add_binary_strings {n1 n2} {
set answer [list]
set carry 0
foreach d1 [list_reverse [split $n1 ""]] \
d2 [list_reverse [split $n2 ""]] \
{
if {$d1 eq ""} {set d1 0}
if {$d2 eq ""} {set d2 0}
switch -exact [set sum [expr {$d1 + $d2 + $carry}]] {
0 -
1 { set carry 0 }
2 { set sum 0; set carry 1 }
3 { set sum 1; set carry 1 }
}
lappend answer $sum
}
lappend answer $carry
return [string trimleft [join [list_reverse $answer] ""] 0]
}
set n1 100010111
set n2 1011011
puts "$n1 + $n2 = [add_binary_strings $n1 $n2]"