I'm trying to (efficiently) calculate the arrival date of a package given a start date and number of business days it is supposed to take to arrive. I think this might be of interest to others. Here's my first cut at it:
proc add_days {start days} {
set 1day [expr {3600 * 24}]
set end [expr {$start + [days2seconds $days]}]
set diff [expr {$end - $start}]
set weeks [expr {$diff / ($1day * 7)}]
set remainder [expr {($diff - $weeks * $1day * 7) / $1day}]
set startdow [clock format $start -format "%u"]
set enddow [clock format $end -format "%u"]
set add 0
incr add [expr {$weeks * 2}]
incr add [expr {$startdow > $enddow ? 2 : 0}]
incr add [expr {$startdow == 6 ? 2 : 0}]
incr add [expr {$startdow == 7 ? 1 : 0}]
set realend [expr {$end + $add * $1day}]
set realenddow [clock format $realend -format "%u"]
set add [expr {$realenddow == 6 ? 2 : 0}]
incr add [expr {$realenddow == 7 ? 2 : 0}]
puts "ordered on [clock format $start] and should take $days days"
puts "arrival on [clock format [expr {$realend + $add * $1day}]]"
}