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arm: Add string-fza.h

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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.

Checked on armv7-linux-gnueabihf

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Richard Henderson 2023-01-10 18:01:04 -03:00 • committed by Adhemerval Zanella
parent 120ad6ed1a
commit 885306b2f6
1 changed files with 67 additions and 0 deletions

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sysdeps/arm/armv6t2/string-fza.h Normal file
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/* Zero byte detection; basics. ARM version.
Copyright (C) 2023 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-misc.h>
#include <string-optype.h>
/* The functions return a byte mask. */
typedef op_t find_t;
/* This function returns at least one bit set within every byte
of X that is zero. */
static __always_inline find_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 ones = repeat_bytes (0x01);
return __builtin_arm_uqsub8 (ones, x);
}
/* Identify bytes that are equal between X1 and X2. */
static __always_inline find_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 __always_inline find_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 __always_inline find_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
#endif /* _STRING_FZA_H */