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big: Add internal_int_exponent_mod.

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Jeroen van Rijn
2021-09-01 12:33:33 +02:00
parent a056e19434
commit 7d7ed6b95f
2 changed files with 63 additions and 66 deletions
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2
core/math/big/example.odin
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@@ -218,7 +218,7 @@ demo :: proc() {
set(b, 6);
set(c, 131);
if err := _private_int_exponent_mod(res, a, b, c, 1); err != nil {
if err := internal_int_exponent_mod(res, a, b, c); err != nil {
fmt.printf("Error: %v\n", err);
}

127
core/math/big/prime.odin
View File

@@ -43,73 +43,70 @@ internal_int_prime_is_divisible :: proc(a: ^Int, allocator := context.allocator)
internal_int_exponent_mod :: proc(res, G, X, P: ^Int, allocator := context.allocator) -> (err: Error) {
context.allocator = allocator;
/*
int dr;
/* modulus P must be positive */
if (mp_isneg(P)) {
return MP_VAL;
}
/* if exponent X is negative we have to recurse */
if (mp_isneg(X)) {
mp_int tmpG, tmpX;
mp_err err;
if (!MP_HAS(MP_INVMOD)) {
return MP_VAL;
}
if ((err = mp_init_multi(&tmpG, &tmpX, NULL)) != MP_OKAY) {
return err;
}
/* first compute 1/G mod P */
if ((err = mp_invmod(G, P, &tmpG)) != MP_OKAY) {
goto LBL_ERR;
}
/* now get |X| */
if ((err = mp_abs(X, &tmpX)) != MP_OKAY) {
goto LBL_ERR;
}
/* and now compute (1/G)**|X| instead of G**X [X < 0] */
err = mp_exptmod(&tmpG, &tmpX, P, Y);
LBL_ERR:
mp_clear_multi(&tmpG, &tmpX, NULL);
return err;
}
/* modified diminished radix reduction */
if (MP_HAS(MP_REDUCE_IS_2K_L) && MP_HAS(MP_REDUCE_2K_L) && MP_HAS(S_MP_EXPTMOD) &&
mp_reduce_is_2k_l(P)) {
return s_mp_exptmod(G, X, P, Y, 1);
}
/* is it a DR modulus? default to no */
dr = (MP_HAS(MP_DR_IS_MODULUS) && mp_dr_is_modulus(P)) ? 1 : 0;
/* if not, is it a unrestricted DR modulus? */
if (MP_HAS(MP_REDUCE_IS_2K) && (dr == 0)) {
dr = (mp_reduce_is_2k(P)) ? 2 : 0;
}
/* if the modulus is odd or dr != 0 use the montgomery method */
if (MP_HAS(S_MP_EXPTMOD_FAST) && (mp_isodd(P) || (dr != 0))) {
return s_mp_exptmod_fast(G, X, P, Y, dr);
}
/* otherwise use the generic Barrett reduction technique */
if (MP_HAS(S_MP_EXPTMOD)) {
return s_mp_exptmod(G, X, P, Y, 0);
}
/* no exptmod for evens */
return MP_VAL;
dr: int;
/*
Modulus P must be positive.
*/
return nil;
if internal_is_negative(P) { return .Invalid_Argument; }
/*
If exponent X is negative we have to recurse.
*/
if internal_is_negative(X) {
tmpG, tmpX := &Int{}, &Int{};
defer internal_destroy(tmpG, tmpX);
internal_init_multi(tmpG, tmpX) or_return;
/*
First compute 1/G mod P.
*/
internal_invmod(tmpG, G, P) or_return;
/*
now get |X|.
*/
internal_abs(tmpX, X) or_return;
/*
And now compute (1/G)**|X| instead of G**X [X < 0].
*/
return internal_int_exponent_mod(res, tmpG, tmpX, P);
}
/*
Modified diminished radix reduction.
*/
can_reduce_2k_l := _private_int_reduce_is_2k_l(P) or_return;
if can_reduce_2k_l {
return _private_int_exponent_mod(res, G, X, P, 1);
}
/*
Is it a DR modulus? default to no.
*/
dr = 1 if _private_dr_is_modulus(P) else 0;
/*
If not, is it a unrestricted DR modulus?
*/
if dr == 0 {
reduce_is_2k := _private_int_reduce_is_2k(P) or_return;
dr = 2 if reduce_is_2k else 0;
}
/*
If the modulus is odd or dr != 0 use the montgomery method.
*/
if internal_int_is_odd(P) || dr != 0 {
return _private_int_exponent_mod(res, G, X, P, dr);
}
/*
Otherwise use the generic Barrett reduction technique.
*/
return _private_int_exponent_mod(res, G, X, P, 0);
}
/*