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big: Add sqrt.

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This commit is contained in:
Jeroen van Rijn
2021-08-11 20:59:51 +02:00
parent 9c2468ecf7
commit 2aae1016ab
4 changed files with 77 additions and 37 deletions
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core/math/big/basic.odin
+45
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@@ -13,6 +13,7 @@ package big
import "core:mem"
import "core:intrinsics"
/*
===========================
User-level routines
@@ -748,6 +749,50 @@ int_sqrmod :: proc(remainder, number, modulus: ^Int) -> (err: Error) {
}
sqrmod :: proc { int_sqrmod, };
/*
This function is less generic than `nth_root`, simpler and faster.
*/
int_sqrt :: proc(dest, src: ^Int) -> (err: Error) {
if err = clear_if_uninitialized(dest); err != .None { return err; }
if err = clear_if_uninitialized(src); err != .None { return err; }
/* Must be positive. */
if src.sign == .Negative { return .Invalid_Argument; }
/* Easy out. If src is zero, so is dest. */
if z, _ := is_zero(src); z { return zero(dest); }
/* Set up temporaries. */
t1, t2 := &Int{}, &Int{};
defer destroy(t1, t2);
if err = copy(t1, src); err != .None { return err; }
if err = zero(t2); err != .None { return err; }
/* First approximation. Not very bad for large arguments. */
if err = shr_digit(t1, t1.used / 2); err != .None { return err; }
/* t1 > 0 */
if err = div(t2, src, t1); err != .None { return err; }
if err = add(t1, t1, t2); err != .None { return err; }
if err = shr(t1, t1, 1); err != .None { return err; }
/* And now t1 > sqrt(arg). */
for {
if err = div(t2, src, t1); err != .None { return err; }
if err = add(t1, t1, t2); err != .None { return err; }
if err = shr(t1, t1, 1); err != .None { return err; }
/* t1 >= sqrt(arg) >= t2 at this point */
cm, _ := cmp_mag(t1, t2);
if cm != 1 { break; }
}
swap(dest, t1);
return err;
}
sqrt :: proc { int_sqrt, };
/*
==========================
Low-level routines