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0 pointspcwalton11y ago0 comments

Well, one of the interesting takeaways from the article is that C as specified often does not let you take advantage of your system architecture. The specification has things like GPUs and segmented memory architectures in mind when it forbids you from doing seemingly reasonable things like taking the difference between the addresses of two separately-allocated objects, even though chances are very good what you're trying to do works just fine on all architectures you care about.

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4 comments · 2 top-level

AnimalMuppet11y ago· 2 in thread

Yes and no. The standard specification defines a C that is very portable. It is quite reasonable that you cannot portably take advantage of your system architecture, which means you cannot do it using C as defined by the standard.

But you still can write stuff that looks just like C, that a C compiler will accept, and that lets you take advantage of your system architecture. You just need to understand that a new version of your compiler can break all of your nifty tricks.

ydcvjk11y ago

Finally someone that understands.

Gibbon111y ago

Not really because there are two kinds of c programer out there.

1. Those that communicate with the outside world exclusively via library calls to an operating system.

2. Those that do not.

People that live in world #1, usually don't get people living in world #2. Example.

  // wait for write ready
  while((spi.S & SPI_S_SPTEF_MASK) == 0)
    ;

  spi.D;
  spi.D = data;

Guess what,

No spi.D; is actually important. No just because the program never writes to spi.S does not mean you can delete the while loop. No you cannot reorder any of this and have it work.

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MichaelCrawford11y ago

Ive worked on embedded systems where stuff like that would be a problem, howver I also knew the memory map for my target.

I wanted to make some crypto run faster so i used memcpy on a pointer to a function to copy executable code from slow flash to fast ram.

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