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Long multiplication: Difference between revisions
→{{header|Tcl}}: Task really calls for manual multiplication, so do it...
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(→{{header|Tcl}}: Task really calls for manual multiplication, so do it...) |
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=={{header|Tcl}}==
{{works with|Tcl|8.5}}<br>
Tcl 8.5 supports arbitrary-precision integers, which improves math operations on large integers. It is easy to define our own by following rules for long multiplication; we can then check this against the built-in's result:
<lang tcl>package require Tcl 8.5
proc longmult {x y} {
set digits [lreverse [split $x ""]]
set result {0}
set j -2
foreach m [lreverse [split $y ""]] {
set c 0
set i [incr j]
foreach d $digits {
set v [lindex $result [incr i]]
if {$v eq ""} {
lappend result 0
set v 0
}
regexp (.)(.)$ 0[expr {$v + $c + $d*$m}] -> c v
lset result $i $v
}
lappend result $c
}
# Reconvert digit list into a decimal number
set result [string trimleft [join [lreverse $result] ""] 0]
if {$result == ""} then {return 0} else {return $result}
}
puts [set n [expr {2**64}]]
puts [longmult $n $n]
puts [expr {$n * $n}]</lang>
outputs
<pre>18446744073709551616
340282366920938463463374607431768211456
340282366920938463463374607431768211456</pre>
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