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cebugdev

floating point calculation in mobile so slow

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my peers told me to use fixed point arithmetic in substitute to floating point since our device doesnt support float, but i cant find any free libraries on the net that implements fixed point in ANSI C, can u guys help me with this one. perhaps share your fixed point library :) just the basic operations like addition,sub,mult and div., i dont have time to read articles and code it myself since deadline for this module is on wed :(

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You can try to port this one:
http://libtomcrypt.bytemine.net/libtomcrypt.org_80/tfm/index.html
Also check out the Allegro lib, they provide a fixed point implementation:
http://alleg.sourceforge.net/onlinedocs/en/alleg032.html


Or you can roll your own. It's not that difficult. Some hints:

Assume that:
x = a * 2^n
y = b * 2^n
z = c * 2^n
where a, b and c are the real values, x, y and z are fixed point values, n is the number of bits behind the dot.

- addition/subtraction remains the same
- multiplication: c = a * b, so z = x * y * 2^-n
- division: c = a / b, so z = x * 2^n / y
- square root: read the wiki http://en.wikipedia.org/wiki/Shifting_nth-root_algorithm

There are different division algorithms, also available in the wiki:
http://en.wikipedia.org/wiki/Division_%28electronics%29

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If you are usiing ARM CPU you also should get rid of divisions. ARM (9 and 10 IIRC) don't support division and emulate it. Use lookup tables instead.

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