Faster to create new variable or reuse existing one for math calculation?

[tmason]

Hello,

So I have a question that sprung out of curiosity as I was programming; is it better to reuse an existing variable or create a new variable for the following situation:

/* Is this faster: */

glm::mat4 newViewModelMatrix = (*existingViewMatrix) * (*existingModelMatrix);

/* Or is this faster? */

glm::mat4 existingViewModelMatrix; /* declared in class header - initial value assigned in class constructor */

existingViewModelMatrix = (*existingViewMatrix) * (*existingModelMatrix);

Just wondering if it makes a difference or not.

Thank you.

[Mathes]

Hi,

the first is equivalent to the copy constructor.
glm:mat4 newViewModelMatrix ( (*existingViewMatrix) * (*existingModelMatrix) );

So it depends which one is cheaper the assignment or the copy constructor. This varies from class to class and therefore cannot be answered in general.

Regards,
mathes