Clipping

I have 3 Pixel routines 1- Regular pixel 2- Alpha blended pixel 3- Additive blended pixel Bassicly each routine you give them x,y coords colors and shades and they draw a pixel at x,y Inside the routines I check for clipping bassicly to c if the x,y location provided is not in the rectangle specified. I did testing to c if the fram rate drops when i do a pixel level clip test and it didn''t seem to affect the frame rate infact also when I would move the pixels of screen the frame rates would climb. What I did is, draw a 400x400 box using pixel lavel clipping meenning through the for loops test everytime for the clipping for each pixel and then I used the same routine but with out any pixel clipping ofcourse i never moved the box of screen. The results where exactly the same. But when I tested for clipping and moved the box of screen the frame rate climbed for that routin. Does it really matter? I dont c the dif Or should I actually calculate the right width and height once outside the for loops and blit the right sized box