Modular inverse: Difference between revisions
Add Cowgol
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1969
</pre>
=={{header|Cowgol}}==
<lang cowgol>include "cowgol.coh";
sub mulinv(a: int32, b: int32): (t: int32) is
if b<0 then b := -b; end if;
if a<0 then a := b - (-a % b); end if;
t := 0;
var nt: int32 := 1;
var r := b;
var nr := a % b;
while nr != 0 loop
var q := r / nr;
var tmp := nt; nt := t - q*nt; t := tmp;
tmp := nr; nr := r - q*nr; r := tmp;
end loop;
if r>1 then t := -1;
elseif t<0 then t := t + b;
end if;
end sub;
record Pair is
a: int32;
b: int32;
end record;
var data: Pair[] := {
{42, 2017},
{40, 1},
{52, -217},
{-486, 217},
{40, 2018}
};
var i: @indexof data := 0;
while i < @sizeof data loop
print_i32(data[i].a as uint32);
print(", ");
print_i32(data[i].b as uint32);
print(" -> ");
var mi := mulinv(data[i].a, data[i].b);
if mi<0
then print("no inverse");
else print_i32(mi as uint32);
end if;
print_nl();
i := i + 1;
end loop;</lang>
{{out}}
<pre>42, 2017 -> 1969
40, 1 -> 0
52, 4294967079 -> 96
4294966810, 217 -> 121
40, 2018 -> no inverse</pre>
=={{header|Crystal}}==
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