George Peter Staplin July 3 2008 -- Here is a simple package for handling money without floating point. It may not be ideal for everyone -- yet. Feel free to improve this, and extend this page.
It could probably use a money-precision command for setting the precision of the numbers after the decimal point.
JMN This might be a nice start for the API - but as it stands it's wildly inaccurate.
e.g calculate 10% tax on 19.11
%package require money 1.0 %money-value [money/ [money 19.11] 10] 1.1
The point of a money package should not be so much to avoid floating-point operations at all cost - but to operate at a level where the errors are at a minimum and you choose when and with what method you do your rounding. e.g by using cents or even some fraction of a cent as your basic unit for calculation and storage.
Other languages seem to have pushed towards a Decimal datatype for currency work.
Martyn Smith My simple solution was to do all math using integer cents/centimes values and just to display a ./, in the right place when displaying any values, the integer math is very quick and no rounding problems.
#By George Peter Staplin
#Use it, share it, modify it, don't blame me.
package provide money 1.0
proc money value {
lassign [split $value .] dol cents
set dol [expr {$dol + ($cents / 100)}]
set cents [expr {$cents % 100}]
list $dol $cents
}
proc money-value m {
join $m .
}
proc money-pretty m {
return \$[join $m .]
}
proc money+ {a b} {
lassign $a adol acent
lassign $b bdol bcent
set dollars [expr {$adol + $bdol}]
set cents [expr {$acent + $bcent}]
set dollars [expr {$dollars + ($cents / 100)}]
set cents [expr {$cents % 100}]
list $dollars $cents
}
proc money- {a b} {
lassign $a adol acents
lassign $b bdol bcents
set cents [expr {$acents - $bcents}]
if {$cents < 0} {
incr adol -1
set cents [expr {$cents + 100}]
}
set dollars [expr {$adol - $bdol}]
list $dollars $cents
}
proc money* {a integer} {
lassign $a adol acent
set dollars [expr {$adol * $integer}]
set cents [expr {($acent * $integer)}]
set dollars [expr {$dollars + ($cents / 100)}]
set cents [expr {$cents % 100}]
list $dollars $cents
}
proc money/ {a integer} {
lassign $a adol acent
set cents [expr {$acent / $integer}]
set dollars [expr {$adol / $integer}]
list $dollars $cents
}
set cd [money 12.45]
set car [money 3999.99]
puts "CD + CAR [money-value [money+ $cd $car]]"
puts [money-value [money* [money+ $cd $car] 2]]
puts "44.02 - 12.99: [money-value [money- [money 44.02] [money 12.99]]]"
puts "42.0 / 4: [money-value [money/ [money 42.0] 4]]"
puts "45.5 / 3: [money-value [money/ [money 45.5] 3]]"
puts "42.0 * 42 * 42 = You're rich! = [money-pretty [money* [money* [money 42.0] 42] 42]]"