[v6,03/17] Add string-maskoff.h generic header
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From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Macros to operate on unaligned access for string operations:
- create_mask: create a mask based on pointer alignment to sets up
non-zero bytes before the beginning of the word so a following
operation (such as find zero) might ignore these bytes.
- check_mask: eturn the mask WORD shifted based on S_INT address
value, to ignore values not presented in the aligned word read.
- repeat_bytes: setup an word with each byte being c_in.
- highbit_mask: create a mask with high bit of each byte being 1,
and the low 7 bits being all the opposite of the input.
- word_containing: return the address of the op_t word containing the
addres.
These macros are meant to be used on optimized vectorized string
implementations.
---
sysdeps/generic/string-maskoff.h | 85 ++++++++++++++++++++++++++++++++
1 file changed, 85 insertions(+)
create mode 100644 sysdeps/generic/string-maskoff.h
Comments
On 1/10/23 13:00, Adhemerval Zanella wrote:
> +/* Return the address of the op_t word containing the address P. For
> + instance on address 0x0011223344556677 and op_t with size of 8,
> + it returns 0x0011223344556670. */
> +static __always_inline op_t *
> +word_containing (char const *p)
> +{
> + return (op_t *) ((uintptr_t) p & -sizeof(p));
> +}
sizeof(op_t).
r~
On 10/01/23 22:58, Richard Henderson wrote:
> On 1/10/23 13:00, Adhemerval Zanella wrote:
>> +/* Return the address of the op_t word containing the address P. For
>> + instance on address 0x0011223344556677 and op_t with size of 8,
>> + it returns 0x0011223344556670. */
>> +static __always_inline op_t *
>> +word_containing (char const *p)
>> +{
>> + return (op_t *) ((uintptr_t) p & -sizeof(p));
>> +}
>
> sizeof(op_t).
Ack.
new file mode 100644
@@ -0,0 +1,85 @@
+/* Mask off bits. Generic C 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_MASKOFF_H
+#define _STRING_MASKOFF_H 1
+
+#include <endian.h>
+#include <limits.h>
+#include <stdint.h>
+#include <string-optype.h>
+#include <string-fza.h>
+
+/* 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));
+}
+
+/* Return the mask WORD shifted based on S_INT address value, to ignore
+ values not presented in the aligned word read. */
+static __always_inline op_t
+check_mask (op_t word, uintptr_t s_int)
+{
+ if (__BYTE_ORDER == __LITTLE_ENDIAN)
+ return word >> (CHAR_BIT * (s_int % sizeof (s_int)));
+ else
+ return word << (CHAR_BIT * (s_int % sizeof (s_int)));
+}
+
+/* Setup an word with each byte being c_in. For instance, on a 64 bits
+ machine with input as 0xce the functions returns 0xcececececececece. */
+static __always_inline op_t
+repeat_bytes (unsigned char c_in)
+{
+ return ((op_t)-1 / 0xff) * c_in;
+}
+
+/* Based on mask created by 'create_mask', mask off the high bit of each
+ byte in the mask. It is used to mask off undesirable bits from an
+ aligned read from an unaligned pointer, and also taking care to avoid
+ match possible bytes meant to be matched. For instance, on a 64 bits
+ machine with a mask created from a pointer with an alignment of 3
+ (0x0000000000ffffff) the function returns 0x7f7f7f0000000000 for BE
+ and 0x00000000007f7f7f for LE. */
+static __always_inline op_t
+highbit_mask (op_t m)
+{
+ return m & repeat_bytes (0x7f);
+}
+
+/* Return the address of the op_t word containing the address P. For
+ instance on address 0x0011223344556677 and op_t with size of 8,
+ it returns 0x0011223344556670. */
+static __always_inline op_t *
+word_containing (char const *p)
+{
+ return (op_t *) ((uintptr_t) p & -sizeof(p));
+}
+
+#endif /* _STRING_MASKOFF_H */