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big: Add lcm and its test.

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This commit is contained in:
Jeroen van Rijn
2021-08-11 20:59:52 +02:00
parent 0028cb0258
commit 8b1d8c8453
4 changed files with 89 additions and 14 deletions
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core/math/big/basic.odin
+43
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@@ -1353,6 +1353,49 @@ int_gcd :: proc(res, a, b: ^Int) -> (err: Error) {
gcd :: proc { int_gcd, };
/*
Least Common Multiple.
Computes least common multiple as `|a*b|/(a, b)`
TODO(Jeroen):
- Maybe combine with GCD and have an `_int_gcd_lcm` proc that can return both with work shared.
*/
int_lcm :: proc(res, a, b: ^Int) -> (err: Error) {
if err = clear_if_uninitialized(a, b, res); err != .None { return err; }
t1, t2 := &Int{}, &Int{};
defer destroy(t1, t2);
/*
t1 = get the GCD of the two inputs.
*/
if err = gcd(t1, a, b); err != .None { return err; }
/*
Divide the smallest by the GCD.
*/
if c, _ := cmp_mag(a, b); c == -1 {
/*
Store quotient in `t2` such that `t2 * b` is the LCM.
*/
if err = div(t2, a, t1); err != .None { return err; }
err = mul(res, t2, b);
} else {
/*
Store quotient in `t2` such that `t2 * a` is the LCM.
*/
if err = div(t2, a, t1); err != .None { return err; }
err = mul(res, t2, b);
}
/*
Fix the sign to positive and return.
*/
res.sign = .Zero_or_Positive;
return err;
}
lcm :: proc { int_lcm, };
when size_of(rawptr) == 8 {
_factorial_table := [35]_WORD{
/* f(00): */ 1,