Void *memcpy(void *restrict dest, const void *restrict src, size_t count)Ĭonst ptrdiff_t diff = (char*)dest - src8 Rather than independently track two different pointers, you precalculate the ptrdiff_t between src and dest, then increment only the src (or only dest). One compiler optimization that direct pointer arithmetic (rather than indexed access) sometimes stymies might help on the architectures lacking pre/post increment instructions, if the architecture offers memory retrieval/storage based on a pointer and an offset where both are registers, rather than just fixed offset from register. In times where power consumption has become so much important, I would think that the first thing to do to save power is optimise the software, and what better place to start than the core parts of an operating system? I can't speak for the kernel -though I'm sure it's very optimised actually- but having looked at the glibc code extensively the past years, I can say that it's grossly unoptimised, so much it hurts." Reply Delete Not only that, glibc only includes reference implementations that perform the operations one-byte-at-a-time! How's that for inefficient? We're not talking about dummy unused joke functions here like memfrob(), but really important string and memory functions that are used pretty much everywhere, like strcmp(), strncmp(), strncpy(), etc. Finally, with regard to glibc performance, even if we take into account that some common routines are optimised (like strlen(), memcpy(), memcmp() plus some more), most string functions are NOT optimised. Its my understanding that things like the glibc and related libs are not using any worthwhile SIMD optimised instructions at this time for several routines, perhaps you should investigate and try some options. The example below shows how this can be done when the destination buffer is aligned on a 32-bit address and the source buffer is 8 bits off the alignment: The implementation needs two temporary variables that implement a 64-bit sliding window where the source data is kept temporary while being copied into the destination. The accesses to memory need to be aligned on 32-bit addresses. On such systems it is often expensive to use data types like double and some systems doesn't have a FPU (Floating Point Unit).īy trying to read and write memory in 32 bit blocks as often as possible, the speed of the implementation is increased dramatically, especially when copying data that is not aligned on a 32-bit boundary. The goal with the C implementation of memcpy() was to get portable code mainly for embedded systems. It is of course possible to read larger chunks of data on some targets with wider data bus and wider data registers. My first improvement to my co-worker's original was to read 32 bits at the time from the memory. In most systems, the CPU clock runs at much higher frequency than the speed of the memory bus. ![]() The following paragraphs contain descriptions to some of the techniques used in the final implementation. ![]() Both our implementations got better and better and looked more alike and finally we had an implementation that was very fast and that beats both the native library routines in Windows and Linux, especially when the memory to be copied is not aligned on a 32 bit boundary. I made an implementation, which was quite a lot faster than my co-vorker's and this started a friendly competition to make the fastest portable C implementation of memcpy(). When looking at his code, I found several places where improvements could be made. ![]() ![]() His implementation was faster than many standardized C library routines found in the embedded market. The story began when a co-worker of mine made an implementation of memcpy that he was very proud of. This implementation has been used successfully in several project where performance needed a boost, including the iPod Linux port, the xHarbour Compiler, the pymat python-Matlab interface, the Inspire IRCd client, and various PSP games. With 320+ video and 50+ audio codecs supported, it helps you to convert 4K UHD, MKV, AVCHD, M2TS, MP4, AVI, WMV, MOV, VOB, etc to any video or … Read more Categories Video › Encoders/Converter/DIVX Related Tags macx hd video converter pro for windows crack, MacX Video Converter Pro 2022 Crack, macx video converter pro 6.0.4 license code, macx video converter pro 6.2.0 serial, macx video converter pro 6.This article describes a fast and portable memcpy implementation that can replace the standard library version of memcpy when higher performance is needed. MacX Video Converter Pro 6.8.2 License Key Free Download MacX Video Converter Pro 6.8.2 best all-in-one video converter for Mac to download, convert, edit, and record videos.
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