Richard Suchenwirth 2006-12-06 - Here's a way of converting an ASCII string of up to 9 characters from and to a
wide integer, in which a sequence of 7 bits corresponds to one character. 7*9 = 63, so the integers will always be non-negative, as the sign bit is always 0:
proc base128'encode str {
if {[string length $str]>9} {error "string must be 0..9 characters long"}
set res 0
foreach c [split $str ""] {
set res [expr {wide($res)<<7 | [scan $c %c]%128}]
}
set res
}
proc base128'decode int {
set res ""
while {$int != 0} {
set res [format %c [expr {$int % 128}]]$res
set int [expr {$int >> 7}]
}
set res
}Examples:
% base128'encode ""
0
% base128'encode hello
28130883183
% base128'encode "Tcl & Tk"
47726922213894763
% base128'decode 47726922213894763
Tcl & Tk
