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big: Split up int_mod_bits (res = val % (1 << bits))

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This commit is contained in:
Jeroen van Rijn
2021-08-07 18:00:07 +02:00
parent c3db24f834
commit d4a03acbc3
2 changed files with 47 additions and 37 deletions
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core/math/big/basic.odin
+4 -32
View File
@@ -321,39 +321,11 @@ lcm :: proc { int_lcm, };
remainder = numerator % (1 << bits)
*/
int_mod_bits :: proc(remainder, numerator: ^Int, bits: int) -> (err: Error) {
if err = clear_if_uninitialized(remainder); err != nil { return err; }
if err = clear_if_uninitialized(numerator); err != nil { return err; }
if remainder == nil || numerator == nil { return .Invalid_Pointer; }
if err = clear_if_uninitialized(remainder, numerator); err != nil { return err; }
if bits < 0 { return .Invalid_Argument; }
if bits == 0 { return zero(remainder); }
/*
If the modulus is larger than the value, return the value.
*/
err = copy(remainder, numerator);
if bits >= (numerator.used * _DIGIT_BITS) || err != nil {
return;
}
/*
Zero digits above the last digit of the modulus.
*/
zero_count := (bits / _DIGIT_BITS);
zero_count += 0 if (bits % _DIGIT_BITS == 0) else 1;
/*
Zero remainder. Special case, can't use `zero_unused`.
*/
if zero_count > 0 {
mem.zero_slice(remainder.digit[zero_count:]);
}
/*
Clear the digit that is not completely outside/inside the modulus.
*/
remainder.digit[bits / _DIGIT_BITS] &= DIGIT(1 << DIGIT(bits % _DIGIT_BITS)) - DIGIT(1);
return clamp(remainder);
return #force_inline internal_int_mod_bits(remainder, numerator, bits);
}
mod_bits :: proc { int_mod_bits, };
mod_bits :: proc { int_mod_bits, };
core/math/big/internal.odin
+43 -5
View File
@@ -876,6 +876,44 @@ internal_int_gcd_lcm :: proc(res_gcd, res_lcm, a, b: ^Int) -> (err: Error) {
return #force_inline _private_int_gcd_lcm(res_gcd, res_lcm, a, b);
}
/*
remainder = numerator % (1 << bits)
Assumes `remainder` and `numerator` both not to be `nil` and `bits` to be >= 0.
*/
internal_int_mod_bits :: proc(remainder, numerator: ^Int, bits: int) -> (err: Error) {
/*
Everything is divisible by 1 << 0 == 1, so this returns 0.
*/
if bits == 0 { return zero(remainder); }
/*
If the modulus is larger than the value, return the value.
*/
err = copy(remainder, numerator);
if bits >= (numerator.used * _DIGIT_BITS) || err != nil {
return;
}
/*
Zero digits above the last digit of the modulus.
*/
zero_count := (bits / _DIGIT_BITS);
zero_count += 0 if (bits % _DIGIT_BITS == 0) else 1;
/*
Zero remainder. Special case, can't use `zero_unused`.
*/
if zero_count > 0 {
mem.zero_slice(remainder.digit[zero_count:]);
}
/*
Clear the digit that is not completely outside/inside the modulus.
*/
remainder.digit[bits / _DIGIT_BITS] &= DIGIT(1 << DIGIT(bits % _DIGIT_BITS)) - DIGIT(1);
return clamp(remainder);
}
internal_int_zero_unused :: #force_inline proc(dest: ^Int, old_used := -1) {
/*
@@ -1590,7 +1628,7 @@ _private_int_gcd_lcm :: proc(res_gcd, res_lcm, a, b: ^Int) -> (err: Error) {
/*
Subtract smallest from largest.
*/
if err = sub(v, v, u); err != nil { return err; }
if err = internal_sub(v, v, u); err != nil { return err; }
/*
Divide out all factors of two.
@@ -1622,14 +1660,14 @@ _private_int_gcd_lcm :: proc(res_gcd, res_lcm, a, b: ^Int) -> (err: Error) {
/*
Store quotient in `t2` such that `t2 * b` is the LCM.
*/
if err = div(res_lcm, a, temp_gcd_res); err != nil { return err; }
err = mul(res_lcm, res_lcm, b);
if err = internal_div(res_lcm, a, temp_gcd_res); err != nil { return err; }
err = internal_mul(res_lcm, res_lcm, b);
} else {
/*
Store quotient in `t2` such that `t2 * a` is the LCM.
*/
if err = div(res_lcm, a, temp_gcd_res); err != nil { return err; }
err = mul(res_lcm, res_lcm, b);
if err = internal_div(res_lcm, a, temp_gcd_res); err != nil { return err; }
err = internal_mul(res_lcm, res_lcm, b);
}
if res_gcd != nil {