[PATCH v6 14/17] alpha: Add string-fzb.h and string-fzi.h

[Richard Henderson]

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~