During February 2002, Gerald Lester posted version 0.1 of the following code, designed to be a script level package for performing precise math against decimal numbers.
For more precision from a C based extension, check out mpexpr.
A similar Tcl-based implementation is at Arbitrary precision math procedures.
package provide packedDecimal 0.1
namespace eval packedDecimal {
namespace export add subtract multiply divide setDecimals
variable decimals 2
variable formatString {%d.%2.2d}
variable carry 100
}
proc packedDecimal::add {a b} {
variable decimals
variable formatString
scan $a %d.%d a1 a2
scan $b %d.%d b1 b2
incr a2 $b2
if {[string length $a2] > $decimals} then {
incr a1 1
set a2 [string range $a2 1 end]
}
incr a1 $b1
return [format $formatString $a1 $a2]
}
proc packedDecimal::subtract {a b} {
variable decimals
variable formatString
variable carry
scan $a %d.%d a1 a2
scan $b %d.%d b1 b2
incr a2 -$b2
if {$a2 < 0} then {
incr b1 1
set a2 [expr {$carry + $a2}]
}
incr a1 -$b1
return [format $formatString $a1 $a2]
}
proc packedDecimal::multiple {a b} {
variable decimals
variable formatString
return -code error {Sorry, Multiple is not yet implemented!}
}
proc packedDecimal::divide {a b} {
variable decimals
variable formatString
return -code error {Sorry, Divide is not yet implemented!}
}
proc packedDecimal::setDecimals {a} {
variable decimals
variable formatString
variable carry 100
set formatString [format {%%d.%%%d.%dd} $a $a]
set decimals $a
set carry [format "1%${a}.${a}d" 0]
return;
}
proc packedDecimal::getDecimals {} {
variable decimals
return $decimals
}