Question

While I was reading through glibc source code, I found this interesting comment in strcat.c . Can anyone explain how does this optimization work?

/* Make S1 point before the next character, so we can increment
         it while memory is read (wins on pipelined cpus).  */
      s1 -= 2;

      do
        {
          c = *s2++;
          *++s1 = c;
        }
      while (c != '\0');
Était-ce utile?

La solution

Pipelined CPU's can do some things in parallel. For instance, it can increment the address of S1, while reading from the address it used to point at.

Autres conseils

It just means that the increment of s1 can be done while a char is being fetched from *s2, so it's free.

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