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

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

On 1/17/23 08:49, Adhemerval Zanella Netto wrote:
> 
> 
> 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.

The thing is... leaving things as they are is probably better for HPPA and SH, which get 
to use their boolean byte comparison instructions.

The prior code in strchr(nul) was trying to prevent matches vs both 0 and C, consuming at 
least 4 extra insns (possibly more with the constant loads).  The new code in strchrnul 
may be better (or at least close) everywhere.

But perhaps simplicity demands removal in strlen as well?

> The word_containing can be removed as well in favor of PTR_ALIGN macros and

Good idea.

> I will rename the header to string-repeat_bytes.h.

Or merge with string-extbyte.h and name string-misc.h?


r~