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big: Add mod_power_of_two.

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This commit is contained in:
Jeroen van Rijn
2021-07-22 18:12:19 +02:00
parent 78c0877994
commit d4d863c4db
2 changed files with 55 additions and 12 deletions
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59
core/math/big/basic.odin
View File

@@ -322,7 +322,7 @@ int_sub_digit :: proc(dest, a: ^Int, digit: DIGIT) -> (err: Error) {
carry := dest.digit[i] >> ((size_of(DIGIT) * 8) - 1);
dest.digit[i] &= _MASK;
}
}
}
zero_count := old_used - dest.used;
/*
@@ -374,13 +374,13 @@ int_halve :: proc(dest, src: ^Int) -> (err: Error) {
Shift the current digit, add in carry and store.
*/
dest.digit[x] = (src_digit >> 1) | (fwd_carry << (_DIGIT_BITS - 1));
/*
Forward carry to next iteration.
*/
fwd_carry = carry;
}
/*
Forward carry to next iteration.
*/
fwd_carry = carry;
}
zero_count := old_used - dest.used;
zero_count := old_used - dest.used;
/*
Zero remainder.
*/
@@ -447,7 +447,7 @@ int_double :: proc(dest, src: ^Int) -> (err: Error) {
*/
dest.digit[dest.used] = 1;
}
zero_count := old_used - dest.used;
zero_count := old_used - dest.used;
/*
Zero remainder.
*/
@@ -463,6 +463,49 @@ int_double :: proc(dest, src: ^Int) -> (err: Error) {
double :: proc { int_double, };
shl1 :: double;
/*
dest = src % (2^power);
*/
int_mod_power_of_two :: proc(dest, src: ^Int, power: int) -> (err: Error) {
dest := dest; src := src;
if err = clear_if_uninitialized(dest); err != .None {
return err;
}
if err = clear_if_uninitialized(src); err != .None {
return err;
}
if power < 0 { return .Invalid_Argument; }
if power == 0 { return zero(dest); }
/*
If the modulus is larger than the value, return the value.
*/
err = copy(dest, src);
if power >= (src.used * _DIGIT_BITS) || err != .None {
return;
}
/*
Zero digits above the last digit of the modulus.
*/
zero_count := (power / _DIGIT_BITS) + 0 if (power % _DIGIT_BITS == 0) else 1;
/*
Zero remainder.
*/
if zero_count > 0 {
mem.zero_slice(dest.digit[zero_count:]);
}
/*
Clear the digit that is not completely outside/inside the modulus.
*/
dest.digit[power / _DIGIT_BITS] &= DIGIT(1 << DIGIT(power % _DIGIT_BITS)) - DIGIT(1);
return clamp(dest);
}
mod_power_of_two :: proc { int_mod_power_of_two, };
/*
==========================
Low-level routines

8
core/math/big/example.odin
View File

@@ -57,16 +57,16 @@ demo :: proc() {
a, b, c := &Int{}, &Int{}, &Int{};
defer destroy(a, b, c);
err = set(a, 0);
a.used = 2;
a.digit[1] = 1;
err = set(a, -512);
err = set(b, 1);
err = set(c, -4);
err = mod_power_of_two(a, a, 10);
fmt.printf("%v (%v)\n", int_get_float(a));
print("a", a, 16);
print("a", a, 10);
print("b", b, 10);
print("c", c, 10);