Speeding up the code

[amsami]

Please, can anyone give some ideas on how speed up a c-code?

[guruplus]

take a look at this link
http://www.abarnett.demon.co.uk/tutorial.html#INTEGERS 

[z05DSL3A]

I like a site on optimization that starts with a quote along the lines off:

"More computing sins are committed in the name of efficiency 
(without necessarily achieving it) than for any other single reason - 
including blind stupidity."
                                                                                       - W.A. Wulf

http://www.tantalon.com/pete/cppopt/main.htm uses that exact quote.

but generaly google "C Optimization Strategies" or "C Optimization Techniques " and you should find a welth of information.