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big: Add internal_invmod.

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Jeroen van Rijn
2021-08-13 14:55:53 +02:00
parent f72a0de074
commit 37be8d4091
1 changed files with 28 additions and 1 deletions
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29
core/math/big/internal.odin
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@@ -1740,6 +1740,29 @@ internal_int_neg :: proc(dest, src: ^Int, allocator := context.allocator) -> (er
}
internal_neg :: proc { internal_int_neg, };
/*
hac 14.61, pp608.
*/
internal_int_inverse_modulo :: proc(dest, a, b: ^Int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
/*
For all n in N and n > 0, n = 0 mod 1.
*/
if internal_is_positive(a) && internal_cmp(b, 1) == 0 { return internal_zero(dest); }
/*
`b` cannot be negative and has to be > 1
*/
if internal_is_negative(b) && internal_cmp(b, 1) != 1 { return .Invalid_Argument; }
/*
If the modulus is odd we can use a faster routine instead.
*/
if internal_is_odd(b) { return _private_inverse_modulo_odd(dest, a, b); }
return _private_inverse_modulo(dest, a, b);
}
internal_invmod :: proc{ internal_int_inverse_modulo, };
/*
Helpers to extract values from the `Int`.
@@ -1991,7 +2014,11 @@ internal_int_get :: proc(a: ^Int, $T: typeid) -> (res: T, err: Error) where intr
internal_get :: proc { internal_int_get, };
internal_int_get_float :: proc(a: ^Int) -> (res: f64, err: Error) {
l := min(a.used, 17); // log2(max(f64)) is approximately 1020, or 17 legs.
/*
log2(max(f64)) is approximately 1020, or 17 legs with the 64-bit storage.
*/
legs :: 1020 / _DIGIT_BITS;
l := min(a.used, legs);
fac := f64(1 << _DIGIT_BITS);
d := 0.0;