 Unsigned integer division by 10
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Bjørn
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Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
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My main problem with that method is that if I multiply with anything larger than 1, numbers like 0xFFFFFFFF will overflow a 32 bit register. I might need 96 bits to make sure that method works with all numbers and that is going to be quite slow.
With a 64 bit multiply (n*429496730)>>32 works for all numbers up to 1 073 741 829 and (n*1717986919)>>34 works for all numbers up to 2 863 311 539.
Edit:
((n-(n>>30))*429496730)>>32 works on all 32 bit numbers and takes at most 7 cycles on an ARM7 with a 64 bit multiplier. That is more than twice as fast as I was looking for.
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