Re: [PATCH 05/25] tools lib: Adopt memchr_inv() from kernel

Arnaldo Carvalho de Melo
2020-11-26T17:42:50Z

Em Thu, Nov 26, 2020 at 06:00:06PM +0100, Jiri Olsa escreveu:
> We'll use it to check for undefined/zero data.

Thanks, applied.

- Arnaldo

> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> tools/include/linux/string.h | 1 +
> tools/lib/string.c | 58 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 59 insertions(+)
>
> diff --git a/tools/include/linux/string.h b/tools/include/linux/string.h
> index 5e9e781905ed..db5c99318c79 100644
> --- a/tools/include/linux/string.h
> +++ b/tools/include/linux/string.h
> @@ -46,4 +46,5 @@ extern char * __must_check skip_spaces(const char *);
>
> extern char *strim(char *);
>
> +extern void *memchr_inv(const void *start, int c, size_t bytes);
> #endif /* _TOOLS_LINUX_STRING_H_ */
> diff --git a/tools/lib/string.c b/tools/lib/string.c
> index f645343815de..8b6892f959ab 100644
> --- a/tools/lib/string.c
> +++ b/tools/lib/string.c
> @@ -168,3 +168,61 @@ char *strreplace(char *s, char old, char new)
> *s = new;
> return s;
> }
> +
> +static void *check_bytes8(const u8 *start, u8 value, unsigned int bytes)
> +{
> + while (bytes) {
> + if (*start != value)
> + return (void *)start;
> + start++;
> + bytes--;
> + }
> + return NULL;
> +}
> +
> +/**
> + * memchr_inv - Find an unmatching character in an area of memory.
> + * @start: The memory area
> + * @c: Find a character other than c
> + * @bytes: The size of the area.
> + *
> + * returns the address of the first character other than @c, or %NULL
> + * if the whole buffer contains just @c.
> + */
> +void *memchr_inv(const void *start, int c, size_t bytes)
> +{
> + u8 value = c;
> + u64 value64;
> + unsigned int words, prefix;
> +
> + if (bytes <= 16)
> + return check_bytes8(start, value, bytes);
> +
> + value64 = value;
> + value64 |= value64 << 8;
> + value64 |= value64 << 16;
> + value64 |= value64 << 32;
> +
> + prefix = (unsigned long)start % 8;
> + if (prefix) {
> + u8 *r;
> +
> + prefix = 8 - prefix;
> + r = check_bytes8(start, value, prefix);
> + if (r)
> + return r;
> + start += prefix;
> + bytes -= prefix;
> + }
> +
> + words = bytes / 8;
> +
> + while (words) {
> + if (*(u64 *)start != value64)
> + return check_bytes8(start, value, 8);
> + start += 8;
> + words--;
> + }
> +
> + return check_bytes8(start, value, bytes % 8);
> +}
> --
> 2.26.2
>

--

- Arnaldo