From: Richard Henderson <richard.henderson@linaro.org>
To: Adhemerval Zanella <adhemerval.zanella@linaro.org>,
libc-alpha@sourceware.org,
Noah Goldstein <goldstein.w.n@gmail.com>
Subject: Re: [PATCH v6 14/17] alpha: Add string-fzb.h and string-fzi.h
Date: Tue, 10 Jan 2023 18:45:20 -0800 [thread overview]
Message-ID: <da06001c-2b64-f371-558d-37ef359ac357@linaro.org> (raw)
In-Reply-To: <20230110210106.1457686-15-adhemerval.zanella@linaro.org>
On 1/10/23 13:01, Adhemerval Zanella wrote:
> From: Richard Henderson <richard.henderson@linaro.org>
>
> While alpha has the more important string functions in assembly,
> there are still a few for find the generic routines are used.
>
> Use the CMPBGE insn, via the builtin, for testing of zeros. Use a
> simplified expansion of __builtin_ctz when the insn isn't available.
>
> Checked on alpha-linux-gnu.
> ---
> sysdeps/alpha/string-fzb.h | 52 +++++++++++++++++
> sysdeps/alpha/string-fzi.h | 113 +++++++++++++++++++++++++++++++++++++
> 2 files changed, 165 insertions(+)
> create mode 100644 sysdeps/alpha/string-fzb.h
> create mode 100644 sysdeps/alpha/string-fzi.h
>
> diff --git a/sysdeps/alpha/string-fzb.h b/sysdeps/alpha/string-fzb.h
> new file mode 100644
> index 0000000000..e3934ba413
> --- /dev/null
> +++ b/sysdeps/alpha/string-fzb.h
> @@ -0,0 +1,52 @@
> +/* Zero byte detection; boolean. Alpha 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_FZB_H
> +#define _STRING_FZB_H 1
> +
> +#include <sys/cdefs.h>
> +#include <string-optype.h>
> +
> +/* Note that since CMPBGE creates a bit mask rather than a byte mask,
> + we cannot simply provide a target-specific string-fza.h. */
> +
> +/* Determine if any byte within X is zero. This is a pure boolean test. */
> +
> +static __always_inline _Bool
> +has_zero (op_t x)
> +{
> + return __builtin_alpha_cmpbge (0, x) != 0;
> +}
> +
> +/* Likewise, but for byte equality between X1 and X2. */
> +
> +static __always_inline _Bool
> +has_eq (op_t x1, op_t x2)
> +{
> + return has_zero (x1 ^ x2);
> +}
> +
> +/* Likewise, but for zeros in X1 and equal bytes between X1 and X2. */
> +
> +static __always_inline _Bool
> +has_zero_eq (op_t x1, op_t x2)
> +{
> + return has_zero (x1) | has_eq (x1, x2);
> +}
> +
> +#endif /* _STRING_FZB_H */
> diff --git a/sysdeps/alpha/string-fzi.h b/sysdeps/alpha/string-fzi.h
> new file mode 100644
> index 0000000000..bc2f0bdc91
> --- /dev/null
> +++ b/sysdeps/alpha/string-fzi.h
> @@ -0,0 +1,113 @@
> +/* string-fzi.h -- zero byte detection; indices. Alpha 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_FZI_H
> +#define _STRING_FZI_H
> +
> +#include <limits.h>
> +#include <string-optype.h>
> +
> +/* Note that since CMPBGE creates a bit mask rather than a byte mask,
> + we cannot simply provide a target-specific string-fza.h. */
> +
> +/* A subroutine for the index_zero functions. Given a bitmask C,
> + return the index of the first bit set in memory order. */
> +
> +static __always_inline unsigned int
> +index_first (unsigned long int c)
> +{
> +#ifdef __alpha_cix__
> + return __builtin_ctzl (c);
> +#else
> + c = c & -c;
> + return (c & 0xf0 ? 4 : 0) + (c & 0xcc ? 2 : 0) + (c & 0xaa ? 1 : 0);
> +#endif
> +}
> +
> +/* Similarly, but return the (memory order) index of the last bit
> + that is non-zero. Note that only the least 8 bits may be nonzero. */
> +
> +static __always_inline unsigned int
> +index_last (unsigned long int x)
> +{
> +#ifdef __alpha_cix__
> + return __builtin_clzl (x) ^ 63;
> +#else
> + unsigned r = 0;
> + if (x & 0xf0)
> + r += 4;
> + if (x & (0xc << r))
> + r += 2;
> + if (x & (0x2 << r))
> + r += 1;
> + return r;
> +#endif
> +}
> +
> +/* Given a word X that is known to contain a zero byte, return the
> + index of the first such within the word in memory order. */
> +
> +static __always_inline unsigned int
> +index_first_zero (op_t x)
> +{
> + return index_first (__builtin_alpha_cmpbge (0, x));
The header split has drifted somewhat since the original: string-fza.h is missing and
check_mask() seems misplaced.
In particular, from strchrnul,
+ op_t mask = check_mask (find_zero_eq_all (word, repeated_c), s_int);
+ if (mask != 0)
+ return (char *) str + index_first (mask);
We're using the generic find_zero_eq_all, then (correctly, for the moment) the generic
check_mask, and then incorrectly the alpha-specific index_first.
We want to use an alpha-specific find_zero_eq_all (using cmpbge), an alpha-specific
check_mask (shifting by bits, not bytes), and an alpha-specific index_first (searching
only 8 low bits, not a full ctz).
I wonder if it makes sense to introduce a target-specific find_t, making it clear that
it's not the same type as op_t (for alpha, int instead of unsigned long (uint8_t having
it's own issues on ancient alpha ev5)).
I think check_mask (possibly renamed shift_find?) should belong in string-fza.h to match
the implementation therein, or within a new header (possibly along with find_t?).
Anyway, even the current set of headers would work, so long as Alpha implements all of them.
r~
next prev parent reply other threads:[~2023-01-11 2:45 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-10 21:00 [PATCH v6 00/17] Improve generic string routines Adhemerval Zanella
2023-01-10 21:00 ` [PATCH v6 01/17] Parameterize op_t from memcopy.h Adhemerval Zanella
2023-01-10 21:00 ` [PATCH v6 02/17] Parameterize OP_T_THRES " Adhemerval Zanella
2023-01-10 21:00 ` [PATCH v6 03/17] Add string-maskoff.h generic header Adhemerval Zanella
2023-01-11 1:58 ` Richard Henderson
2023-01-11 13:39 ` Adhemerval Zanella Netto
2023-01-10 21:00 ` [PATCH v6 04/17] Add string vectorized find and detection functions Adhemerval Zanella
2023-01-11 2:25 ` Richard Henderson
2023-01-11 13:42 ` Adhemerval Zanella Netto
2023-01-11 19:56 ` Noah Goldstein
2023-01-10 21:00 ` [PATCH v6 05/17] string: Improve generic strlen Adhemerval Zanella
2023-01-10 21:00 ` [PATCH v6 06/17] string: Improve generic strnlen Adhemerval Zanella
2023-01-10 21:00 ` [PATCH v6 07/17] string: Improve generic strchr Adhemerval Zanella
2023-01-10 21:00 ` [PATCH v6 08/17] string: Improve generic strchrnul Adhemerval Zanella
2023-01-10 21:00 ` [PATCH v6 09/17] string: Improve generic strcmp Adhemerval Zanella
2023-01-10 21:00 ` [PATCH v6 10/17] string: Improve generic memchr Adhemerval Zanella
2023-01-10 21:01 ` [PATCH v6 11/17] string: Improve generic memrchr Adhemerval Zanella
2023-01-10 21:01 ` [PATCH v6 12/17] hppa: Add memcopy.h Adhemerval Zanella
2023-01-10 21:01 ` [PATCH v6 13/17] hppa: Add string-fzb.h and string-fzi.h Adhemerval Zanella
2023-01-10 21:01 ` [PATCH v6 14/17] alpha: " Adhemerval Zanella
2023-01-11 2:45 ` Richard Henderson [this message]
2023-01-11 17:27 ` Adhemerval Zanella Netto
2023-01-10 21:01 ` [PATCH v6 15/17] arm: Add string-fza.h Adhemerval Zanella
2023-01-10 21:01 ` [PATCH v6 16/17] powerpc: " Adhemerval Zanella
2023-01-11 1:18 ` Carlos Seo
2023-01-10 21:01 ` [PATCH v6 17/17] sh: Add string-fzb.h Adhemerval Zanella
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