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big: Timed factorial.

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This commit is contained in:
Jeroen van Rijn
2021-08-02 22:23:39 +02:00
parent a27612ec6a
commit 627872db97
4 changed files with 35 additions and 24 deletions
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26
core/math/big/basic.odin
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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].

6
core/math/big/build.bat
View File

@@ -1,10 +1,10 @@
@echo off
:odin run . -vet
odin run . -vet
: -o:size -no-bounds-check
:odin build . -build-mode:shared -show-timings -o:minimal -use-separate-modules
:odin build . -build-mode:shared -show-timings -o:size -use-separate-modules -no-bounds-check
:odin build . -build-mode:shared -show-timings -o:size -use-separate-modules
odin build . -build-mode:shared -show-timings -o:speed -use-separate-modules -no-bounds-check
:odin build . -build-mode:shared -show-timings -o:speed -use-separate-modules -no-bounds-check
:odin build . -build-mode:shared -show-timings -o:speed -use-separate-modules
python test.py
:python test.py

2
core/math/big/common.odin
View File

@@ -45,7 +45,7 @@ _MAX_ITERATIONS_ROOT_N :: 500;
/*
Largest `N` for which we'll compute `N!`
*/
_FACTORIAL_MAX_N :: 100_000;
_FACTORIAL_MAX_N :: 1_000_000;
/*
Cutoff to switch to int_factorial_binary_split, and its max recursion level.

25
core/math/big/example.odin
View File

@@ -111,17 +111,30 @@ print :: proc(name: string, a: ^Int, base := i8(10), print_name := false, newlin
}
demo :: proc() {
err: Error;
as: string;
defer delete(as);
a, b, c, d, e, f := &Int{}, &Int{}, &Int{}, &Int{}, &Int{}, &Int{};
defer destroy(a, b, c, d, e, f);
s := time.tick_now();
err = choose(a, 65535, 255);
Timings[.choose].t += time.tick_since(s); Timings[.choose].c += 1;
N :: 5_000;
print("65535 choose 255", a, 10, true, true, true);
fmt.printf("Error: %v\n", err);
s := time.tick_now();
err = factorial(a, N);
Timings[.factorial].t += time.tick_since(s); Timings[.factorial].c += 1;
if err != .None {
fmt.printf("factorial(%v) returned %v\n", N, err);
}
s = time.tick_now();
as, err = itoa(a, 16);
Timings[.itoa].t += time.tick_since(s); Timings[.itoa].c += 1;
if err != .None {
fmt.printf("itoa(factorial(%v), 16) returned %v\n", N, err);
}
fmt.printf("factorial(%v): %v (first 10 hex digits)\n", N, as[:10]);
}
main :: proc() {