[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Speed in Languages and Browser Architectures
I used to do tricks like that, but the modern optimisers are so good I don't even declare C variables as registers any more. In fact it seems anecdotally at least that most modern optimisers work better if I don't try to force variables into registers. Old PDP habits die hard.... Peter Hunsberger wrote: > On 3/2/07, Rick Marshall <rjm@z...> wrote: >> String processing in C is tricky at best. Why? well there's no such >> thing as a string in C... >> >> So Dennis decided a string was an ascii sequence of bytes terminated by >> a 'NUL' (and not containing a NUL). This has lots of limitations and >> over the years the definition and libraries have changed - but string is >> a library, not a language concept. >> >> Then to confound the issue most modern C compilers take advantage of >> native string processing instructions in modern CPUs so many elements of >> the standard C string library are actually compiled into single CPU >> instructions (yeah I know the microcode does lots of instructions). > > But of course you're not really done optimizing until the code is > conditionally compiled to exploit the differences in the performance > of various CPU implementations at the microcode level.... > > I've actually been involved in writing core OS memory and cache > management routines where we played such games; certain CPUs can be > slower on certain instructions so that using multiple instruction > equivalents can perform better. We also played games like manually > pipelining the instruction set to eliminate consecutive register > access, etc. on some CPUs. Can't imagine anyone really engaging in > such practices any more? >
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