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Writing Efficient C Code?

posted by LaminatorX on Sunday March 16 2014, @03:28AM   Printer-friendly
from the premature-optimization-is-the-root-of-all-evil dept.

Subsentient writes:

"I've been writing C for quite some time, but I never followed good conventions I'm afraid, and I never payed much attention to the optimization tricks of the higher C programmers. Sure, I use const when I can, I use the pointer methods for manual string copying, I even use register for all the good that does with modern compilers, but now, I'm trying to write a C-string handling library for personal use, but I need speed, and I really don't want to use inline ASM. So, I am wondering, what would other Soylenters do to write efficient, pure, standards-compliant C?"

 
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  • (Score: 4, Insightful) by FatPhil on Sunday March 16 2014, @11:15AM

    by FatPhil (863) <reversethis-{if.fdsa} {ta} {tnelyos-cp}> on Sunday March 16 2014, @11:15AM (#17148) Homepage
    I got through about half of your post, and didn't see the word "measure" once. Anyone who doesn't start with saying "measure" on the first line of their comment simply doesn't know anything about optimising.

    If the compiler produces shitty object code from your C, you're a shitty C programmer.

    I one ran one of my number-crunching inner loops through (vendor-supplied) simulators for Alpha and Power processors a couple of years back (I've not done any number crunching since then). The same portable C source for both. And the pipeline analyses told me that every single pipeline was 100% saturated, except where instruction dispatch was unable to get new instructions to them, but the instruction dispatch unit was totally saturated every clock tick. Both compilers had produced absolutely perfect object code, and my C code was un-microoptimisable. And as 99.9% of the time was spent in that routine. My job was done. Thank goodness for the high quality of C compilers!
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