Many compilers will implement

      d += *d != c;

with a branch, and depending on the data pattern the branch predictor will be bamboozled. The branchless version would involve a pair of subtractions and some bit banging.

I just tossed together a quick branchless version, and was a little surprised to see that it was significantly slower than the straightforward pointer version on random data: about 1.5x the cycles. Presumably this gap would narrow if checking for char_to_remove was less predictable.

Here's the code I tested. I think it works, but I barely checked it. I'm sure there are better ways to calculate 'increment'. Not sure if these would be enough to close the gap, though.

  void condense_by_removing_branchless(char *z_terminated,  char char_to_remove) { 
    char *condensed = z_terminated;
    while (*z_terminated) {
        *condensed = *z_terminated;
        int diff = *condensed - char_to_remove;
        int increment = -((diff | -diff) >> ((sizeof(int) * 8) - 1)); 
        condensed += increment;
        z_terminated++;
    }
    *condensed = 0;
  }

Gasp! I thought it would be easy to just transfer the compare flag to a general purpose register. I suppose x86 doesn't have such an instruction?

I lied! A quick test shows that GCC uses the x86 SETE instruction (set register on condition equal). Cool.

However, code like this:

    if (x == 14) {
        y = 10;
    } else {
        y = 20;
    }

uses branches, although I think x86-64 has conditional load instructions.