Re: FW: New Defects reported by Coverity Scan for QEMU

[Paolo Bonzini]

On 11/5/21 16:31, Peter Maydell wrote:
> The loop nest in question is (the index must be < 128)
>      for (int offset = 1; offset < 128; offset <<= 1) {
>          for (int k = 0; k < 128; k++) {
>              if (!(k & offset)) {
>                  swap(vector1.ub[k], vector0.ub[k + offset]);
>              }
>          }
>      }
> Basically, it's looking for elements to swap, and the
> "if (!(k & offset))" prevents "k + offset" from overflowing.

It would still be slightly more efficient however to change the loop to 
k < 128 - offset.

Another possibility is to change the inner loop to

for (int k = offset; k < 128; k = (k + 1) | offset)
    swap(vector1.ub[k-offset], vector0.ub[k]);

Paolo