CODEWITHSUNDEEP
mathoptimizationinteger
codymanix
codymanix

Reputation: 29490

How can this function be optimized

Hi I have created this function which be be used to separate a game world into chunks. Each chunk is 32 blocks in size. This formula calculates the start coordinate of a given chunk number of a given world coordinate. It works good but I think it is possible to optimize it but I have no idea. It is important that the formula works with negative numbers.

    static int wrld2chnk(int wrld)
    {
        if (wrld % 32 != 0)
        {
            if (wrld < 0)
                wrld -= (32 + wrld % 32);
            else
                wrld -= wrld % 32;
        }
        return wrld;
    }

// these are example values which can be used to validate the result. The first value in each rpw is the method input, the second is the output:

    (0, 0);
    (31, 0);
    (32, 32);
    (33, 32);
    (-1, -32);
    (-31, -32);
    (-32, -32);
    (-33, -64);
    (-34, -64);
    (-64, -64);
    (-70, -96);

Upvotes: 1

Views: 76

Answers (3)

mcleod_ideafix
mcleod_ideafix

Reputation: 11428

Here's my proposal:

int wrld2chnk (int wrld)
{
  return sgn(wrld)*32*((32*(sgn(wrld)==-1)+abs(wrld))/32);
}

Where sgn(x) is:

#define sgn(x) (((x)>=0)?1:-1)

Although if you are concerned about the ternary operator (I just love it), here you have some alternative implementations for sgn(): Is there a standard sign function (signum, sgn) in C/C++?

Upvotes: 0

Jimmy
Jimmy

Reputation: 304

How about now guys..?? 

if(wrld>0)
wrld = (wrld/32)*32;
else
wrld = ((wrld/32)-1)*32

Upvotes: 0

user555045
user555045

Reputation: 64904

Firstly, the first if can clearly go. The positive case works fine for zero, too:

static int wrld2chnk(int wrld)
{
    if (wrld < 0)
        wrld -= (32 + wrld % 32);
    else
        wrld -= wrld % 32;
    return wrld;
}

But it can be much simpler. You're working around the fact that % cares about the sign. Rounding down to a multiple of a power of two is much easier, just use bitwise AND with the negative of the power of 2 that you're rounding down to:

static int wrld2chnk(int wrld)
{
    return wrld & -32;
}

Upvotes: 6

Related Questions