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

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 16/01/23 17:58, Richard Henderson wrote:
> 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.

Right, I remove the strlen usage then.

> 
>> +/* 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.

The word_containing can be removed as well in favor of PTR_ALIGN macros and
I will rename the header to string-repeat_bytes.h.