I've learned to be extra careful with fast log approximation. I was the tools programmer at a game studio, and few years ago was given the task to speed things

I've learned to be extra careful with fast log approximation. I was the tools programmer at a game studio, and few years ago was given the task to speed things a bit. There was a process that was summing neighbouring pixels, doing some filtering/pre-processing then calculating a value through log, so I've profiled that this was the slowdown, and decided to provide a faster log version. After some googling, and testing it seems everything should've work. Few days later, black mipmaps started to appear. Turns out, I was doing testing in a wrong way, where I was thinking I'm comparing new to old, where I was comparing old to old created by other machine (a bit different results due to be expected). All because I forgot to turn off caching. And my approximation of log2 did not really worked for the most of the numbers involved in. It was using floats, not doubles to begin with, and producing a lot of either NaN's and infinities (hence the black colors). Anyway it was reverted, and had to reconvert everything to get back to normal.