Re: Modulo that 'wraps' the number?

2019-01-21 Thread Matheus via Digitalmars-d-learn
On Monday, 21 January 2019 at 18:39:27 UTC, Steven Schveighoffer 
wrote:

Not a Python user, just hoping to help answer questions :)


Yes I know in fact I'm not the OP but from what I understood from 
his post, he want to replicate, but I may be wrong.


If it's the case, this code may help him:

//DMD64 D Compiler 2.072.2
import std.stdio;
import std.math;

int mod(int i,int j){
if(abs(j)==abs(i)||!j||!i||abs(j)==1){return 0;};
auto m = (i%j);
return (!m||sgn(i)==sgn(j))?(m):(m+j);
}

void main(){
int j,i;
for(j=1;j<9;++j){
for(i=1;i<9;++i){
  writeln(-i, " % ", +j, " = ", (-i).mod(+j));
  writeln(+i, " % ", -j, " = ", (+i).mod(-j));
}
}
}


At least the code above gave me the same results as the Python 
version.


Matheus.


Re: Modulo that 'wraps' the number?

2019-01-21 Thread Steven Schveighoffer via Digitalmars-d-learn

On 1/21/19 10:54 AM, Matheus wrote:

On Monday, 21 January 2019 at 15:01:27 UTC, Steven Schveighoffer wrote:


Probably, this optimizes into better code, but maybe the optimizer 
already does this with the expression above:


auto tmp = n % 3;
if(tmp < 0)
   tmp += 3;

It's just not a nice single expression.



I don't think you can do this, imagine this case:

auto tmp = -1 % -3; // Note divisor in negative too.

tmp will be "-1" which already matches the Python way, so you can't add 
divisor anymore.


If the divisor is unknown, I hadn't considered the case. I was only 
considering the case where the divisor is a constant.


In that case, one can probably determine if the divisor is less than 0 
before starting.


Not a Python user, just hoping to help answer questions :)

-Steve


Re: Modulo that 'wraps' the number?

2019-01-21 Thread Matheus via Digitalmars-d-learn
On Monday, 21 January 2019 at 15:01:27 UTC, Steven Schveighoffer 
wrote:


Probably, this optimizes into better code, but maybe the 
optimizer already does this with the expression above:


auto tmp = n % 3;
if(tmp < 0)
   tmp += 3;

It's just not a nice single expression.

-Steve


I don't think you can do this, imagine this case:

auto tmp = -1 % -3; // Note divisor in negative too.

tmp will be "-1" which already matches the Python way, so you 
can't add divisor anymore.


Matheus.


Re: Modulo that 'wraps' the number?

2019-01-21 Thread Steven Schveighoffer via Digitalmars-d-learn

On 1/21/19 2:33 AM, Paul Backus wrote:

On Monday, 21 January 2019 at 04:52:53 UTC, NaN wrote:

On Sunday, 20 January 2019 at 18:51:54 UTC, Steven Schveighoffer wrote:

On 1/20/19 1:28 PM, faissaloo wrote:

In Python -1%3 == 2 however in D -1%3 == -1
Is there a standard library function or something that gives me the 
Python version of modulo?


Hm... (n%3+3)%3 should work.

-Steve


You only need the

(n % 3) + 3


You need both:

(-3 % 3) + 3 == 3
((-3 % 3) + 3) % 3 == 0


Probably, this optimizes into better code, but maybe the optimizer 
already does this with the expression above:


auto tmp = n % 3;
if(tmp < 0)
   tmp += 3;

It's just not a nice single expression.

-Steve


Re: Modulo that 'wraps' the number?

2019-01-20 Thread Paul Backus via Digitalmars-d-learn

On Monday, 21 January 2019 at 04:52:53 UTC, NaN wrote:
On Sunday, 20 January 2019 at 18:51:54 UTC, Steven 
Schveighoffer wrote:

On 1/20/19 1:28 PM, faissaloo wrote:

In Python -1%3 == 2 however in D -1%3 == -1
Is there a standard library function or something that gives 
me the Python version of modulo?


Hm... (n%3+3)%3 should work.

-Steve


You only need the

(n % 3) + 3


You need both:

(-3 % 3) + 3 == 3
((-3 % 3) + 3) % 3 == 0


Re: Modulo that 'wraps' the number?

2019-01-20 Thread NaN via Digitalmars-d-learn
On Sunday, 20 January 2019 at 18:51:54 UTC, Steven Schveighoffer 
wrote:

On 1/20/19 1:28 PM, faissaloo wrote:

In Python -1%3 == 2 however in D -1%3 == -1
Is there a standard library function or something that gives 
me the Python version of modulo?


Hm... (n%3+3)%3 should work.

-Steve


You only need the

(n % 3) + 3






Re: Modulo that 'wraps' the number?

2019-01-20 Thread Steven Schveighoffer via Digitalmars-d-learn

On 1/20/19 1:28 PM, faissaloo wrote:

In Python -1%3 == 2 however in D -1%3 == -1
Is there a standard library function or something that gives me the 
Python version of modulo?


Hm... (n%3+3)%3 should work.

-Steve