Lair Of The Multimedia Guru

November 23, 2005

Fast approximate max of 2 integers

Maybe you are lucky and your cpu instructon set has a fast maximum_of_2_integers instruction, but more likely you wont be so lucky, in that case a simple bitwise OR might be worth a thought.
Note: max(a,b) ≤ a|b < 2 * max(a,b)
This approximation is surprissingly more usefull then it seems at first

Filed under: Optimization — Michael @ 7:27

Fast greatest common divisor

How do we find the greatest common divisor of 2 integers? Try all integers which are ≤ then the arguments and select the largest which divides both with no remainder, works but its too slow. Or maybe factorize both, take the common factors and multiply them together like they probably told you in school, but thats still far too slow for anything but the small numbers in school excercies
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Filed under: Optimization — Michael @ 7:08

November 22, 2005

Fast integer square root

How to calculate the square root of an integer? (unsigned int)sqrt(x) sure but that is slow on many CPUs (~127 cpu cycles on a P3) it also needs a FPU, which may or may not be a problem, how can we do this quicker? lets see
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Filed under: Optimization — Michael @ 17:21
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