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big: Timed factorial.

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This commit is contained in:
Jeroen van Rijn
2021-08-11 20:59:52 +02:00
parent a27612ec6a
commit 627872db97
4 changed files with 35 additions and 24 deletions
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core/math/big/basic.odin
+12 -14
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@@ -580,9 +580,8 @@ int_mul :: proc(dest, src, multiplier: ^Int) -> (err: Error) {
/*
Early out for `multiplier` is zero; Set `dest` to zero.
*/
if z, _ := is_zero(multiplier); z {
return zero(dest);
}
if z, _ := is_zero(multiplier); z { return zero(dest); }
if z, _ := is_zero(src); z { return zero(dest); }
if src == multiplier {
/*
@@ -748,6 +747,10 @@ int_sqrmod :: proc(remainder, number, modulus: ^Int) -> (err: Error) {
sqrmod :: proc { int_sqrmod, };
/*
TODO: Use Sterling's Approximation to estimate log2(N!) to size the result.
This way we'll have to reallocate less, possibly not at all.
*/
int_factorial :: proc(res: ^Int, n: DIGIT) -> (err: Error) {
if n < 0 || n > _FACTORIAL_MAX_N || res == nil { return .Invalid_Argument; }
@@ -759,12 +762,7 @@ int_factorial :: proc(res: ^Int, n: DIGIT) -> (err: Error) {
return int_factorial_binary_split(res, n);
}
a := &Int{};
defer destroy(a);
if err = set( a, i - 1); err != .None { return err; }
if err = set(res, _factorial_table[i - 1]); err != .None { return err; }
for {
if err = mul(res, res, DIGIT(i)); err != .None || i == n { return err; }
i += 1;
@@ -1168,12 +1166,12 @@ _int_mul_comba :: proc(dest, a, b: ^Int, digits: int) -> (err: Error) {
old_used := dest.used;
dest.used = pa;
for ix = 0; ix < pa; ix += 1 {
/*
Now extract the previous digit [below the carry].
*/
dest.digit[ix] = W[ix];
}
/*
Now extract the previous digit [below the carry].
*/
// for ix = 0; ix < pa; ix += 1 { dest.digit[ix] = W[ix]; }
copy_slice(dest.digit[0:], W[:pa]);
/*
Clear unused digits [that existed in the old copy of dest].