Re: [PATCH v8 03/17] Add string-maskoff.h generic header

[Richard Henderson <richard.henderson@linaro.org>]

On 1/13/23 08:27, Richard Henderson wrote:
> +/* Provide a mask based on the pointer alignment that sets up non-zero
> +   bytes before the beginning of the word.  It is used to mask off
> +   undesirable bits from an aligned read from an unaligned pointer.
> +   For instance, on a 64 bits machine with a pointer alignment of
> +   3 the function returns 0x0000000000ffffff for LE and 0xffffff0000000000
> +   (meaning to mask off the initial 3 bytes).  */
> +static __always_inline op_t
> +create_mask (uintptr_t i)
> +{
> +  i = i % sizeof (op_t);
> +  if (__BYTE_ORDER == __LITTLE_ENDIAN)
> +    return ~(((op_t)-1) << (i * CHAR_BIT));
> +  else
> +    return ~(((op_t)-1) >> (i * CHAR_BIT));
> +}

This has exactly one use, in strlen, which could now use shift_find, like strchrnul.

> +/* Based on mask created by 'create_mask', mask off the high bit of each
> +   byte in the 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 mask created from a pointer with an alignment of 3
> +   (0x0000000000ffffff) the function returns 0x7f7f7f0000000000 for BE
> +   and 0x00000000007f7f7f for LE.  */
> +static __always_inline op_t
> +highbit_mask (op_t m)
> +{
> +  return m & repeat_bytes (0x7f);
> +}

This isn't used at all anymore.

If we remove those two, we're left with repeat_byte and word_containing, which are used, 
but no longer seem to fit the filename of string-maskoff,h, though I can't immediately 
think of something better to use.


r~