Re: [PATCH 15/17] arm: Add string-fza.h

[Richard Earnshaw <Richard.Earnshaw@foss.arm.com>]

On 05/09/2022 16:40, Richard Earnshaw via Libc-alpha wrote:
> 
> 
> On 02/09/2022 21:39, Adhemerval Zanella via Libc-alpha wrote:
>> From: Richard Henderson <rth@twiddle.net>
>>
>> While arm has the more important string functions in assembly,
>> there are still a few generic routines used.
>>
>> Use the UQSUB8 insn for testing of zeros.
> 
> UQSUB8 requires ARMv6 or above.  While that's pretty likely these days, 
> you might want to consider a fall-back for Armv5 or earlier if you still 
> want to support those.
> 

Hmm, nevermind, I've just noticed this is in the armv6t2 directory, so 
ARMv6 is a given.  Sorry for the noise.

R.

> R.
> 
>>
>> Checked on armv7-linux-gnueabihf
>> ---
>>   sysdeps/arm/armv6t2/string-fza.h | 70 ++++++++++++++++++++++++++++++++
>>   1 file changed, 70 insertions(+)
>>   create mode 100644 sysdeps/arm/armv6t2/string-fza.h
>>
>> diff --git a/sysdeps/arm/armv6t2/string-fza.h 
>> b/sysdeps/arm/armv6t2/string-fza.h
>> new file mode 100644
>> index 0000000000..4fe2e8383f
>> --- /dev/null
>> +++ b/sysdeps/arm/armv6t2/string-fza.h
>> @@ -0,0 +1,70 @@
>> +/* Zero byte detection; basics.  ARM version.
>> +   Copyright (C) 2022 Free Software Foundation, Inc.
>> +   This file is part of the GNU C Library.
>> +
>> +   The GNU C Library is free software; you can redistribute it and/or
>> +   modify it under the terms of the GNU Lesser General Public
>> +   License as published by the Free Software Foundation; either
>> +   version 2.1 of the License, or (at your option) any later version.
>> +
>> +   The GNU C Library is distributed in the hope that it will be useful,
>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> +   Lesser General Public License for more details.
>> +
>> +   You should have received a copy of the GNU Lesser General Public
>> +   License along with the GNU C Library; if not, see
>> +   <http://www.gnu.org/licenses/>.  */
>> +
>> +#ifndef _STRING_FZA_H
>> +#define _STRING_FZA_H 1
>> +
>> +#include <string-optype.h>
>> +#include <string-maskoff.h>
>> +
>> +/* This function returns at least one bit set within every byte
>> +   of X that is zero.  */
>> +
>> +static inline op_t
>> +find_zero_all (op_t x)
>> +{
>> +  /* Use unsigned saturated subtraction from 1 in each byte.
>> +     That leaves 1 for every byte that was zero.  */
>> +  op_t ret, ones = repeat_bytes (0x01);
>> +  asm ("uqsub8 %0,%1,%2" : "=r"(ret) : "r"(ones), "r"(x));
>> +  return ret;
>> +}
>> +
>> +/* Identify bytes that are equal between X1 and X2.  */
>> +
>> +static inline op_t
>> +find_eq_all (op_t x1, op_t x2)
>> +{
>> +  return find_zero_all (x1 ^ x2);
>> +}
>> +
>> +/* Identify zero bytes in X1 or equality between X1 and X2.  */
>> +
>> +static inline op_t
>> +find_zero_eq_all (op_t x1, op_t x2)
>> +{
>> +  return find_zero_all (x1) | find_zero_all (x1 ^ x2);
>> +}
>> +
>> +/* Identify zero bytes in X1 or inequality between X1 and X2.  */
>> +
>> +static inline op_t
>> +find_zero_ne_all (op_t x1, op_t x2)
>> +{
>> +  /* Make use of the fact that we'll already have ONES in a 
>> register.  */
>> +  op_t ones = repeat_bytes (0x01);
>> +  return find_zero_all (x1) | (find_zero_all (x1 ^ x2) ^ ones);
>> +}
>> +
>> +/* Define the "inexact" versions in terms of the exact versions.  */
>> +#define find_zero_low        find_zero_all
>> +#define find_eq_low        find_eq_all
>> +#define find_zero_eq_low    find_zero_eq_all
>> +#define find_zero_ne_low    find_zero_ne_all
>> +
>> +#endif /* _STRING_FZA_H */