Re: [PATCH v3 03/18] Add string-maskoff.h generic header

[Paul Eggert <eggert at cs dot ucla dot edu>]

On 01/10/2018 04:47 AM, Adhemerval Zanella wrote:
> +/* Create a mask with high bit of each byte being 1, and the low 7 bits
> +   being all the opposite of the input mask.  It is used to mask off
> +   undesirable bits from an aligned read from an unaligned pointer,
> +   and also taking care to avoid match possible bytes meant to be
> +   matched.  For instance, on a 64 bits machine with a pointer alignment
> +   of 3 the function returns 0x7f7f7f0000000000 (input meant to
> +   be 0xffffff0000000000) for BE and 0x00000000007f7f7f for LE (input
> +   meant to be 0x0000000000ffffff).  */
> +static inline op_t
> +highbit_mask (op_t m)
> +{
> +  return m & ~repeat_bytes (0x80);
> +}

The first line of the comment does not match the implementation, which 
would have to be something like "return (m ^ repeat_bytes (0x7f)) | 
repeat_bytes (0x80);" to match the comment. Also, I suggest replacing 
"~repeat_bytes (0x80)" with "repeat_bytes (0x7f)" as the latter is a bit 
simpler.