what is the fastest algorithm for mapping texture space to file space?

i imagine it is something like taking the texCoords and dividing by the mapsize then droping the fraction component and rounding up or down pending the fraction component size. i’m just musing unresposibly but anyhow i recall reading about the quickest linedrawing routine from world space to screen space. i imagine this would apply here as well. would anyone be willing to give me that algorithm otherwise i will just stick with the first until i have time to look into it. thanks