Re: [PATCH] strcasestr: try to find non-alpha char in NEEDLE

[Carlos O'Donell <carlos@redhat.com>]

On 11/28/23 09:01, James Tirta Halim wrote:
> ---

James,

May you please clarify your copyright assignment status?

Please review "2.1. Copyright FSF or disclaimer" in the contribution checklist:
https://sourceware.org/glibc/wiki/Contribution%20checklist#Copyright_FSF_or_disclaimer


>  string/strcasestr.c | 37 ++++++++++++++++++++++++++++++-------
>  1 file changed, 30 insertions(+), 7 deletions(-)
> 
> diff --git a/string/strcasestr.c b/string/strcasestr.c
> index 2f6b4f8641..65eae2f047 100644
> --- a/string/strcasestr.c
> +++ b/string/strcasestr.c
> @@ -54,7 +54,6 @@
>  #define STRCASESTR __strcasestr
>  #endif
>  
> -
>  /* Find the first occurrence of NEEDLE in HAYSTACK, using
>     case-insensitive comparison.  This function gives unspecified
>     results in multibyte locales.  */
> @@ -63,18 +62,42 @@ STRCASESTR (const char *haystack, const char *needle)
>  {
>    size_t needle_len; /* Length of NEEDLE.  */
>    size_t haystack_len; /* Known minimum length of HAYSTACK.  */
> +  const char *h, *n;
>  
>    /* Handle empty NEEDLE special case.  */
>    if (needle[0] == '\0')
>      return (char *) haystack;
>  
> -  /* Ensure HAYSTACK length is at least as long as NEEDLE length.
> -     Since a match may occur early on in a huge HAYSTACK, use strnlen
> -     and read ahead a few cachelines for improved performance.  */
> -  needle_len = strlen (needle);
> -  haystack_len = __strnlen (haystack, needle_len + 256);
> -  if (haystack_len < needle_len)
> +  /* Try to find a non-alphanumeric character in NEEDLE to pass to
> +     strchr() while checking if HAYSTACK is as long as NEEDLE.  */
> +  for (h = haystack, n = needle; *h && isalpha (*n); ++h, ++n);
> +  if (__glibc_unlikely (*h == '\0'))
>      return NULL;
> +  if (*n) {
> +    size_t shift;
> +    shift = n - needle;
> +    haystack = strchr (h + shift, *n);
> +    if (__glibc_unlikely (haystack == NULL))
> +      return NULL;
> +    haystack -= shift;
> +    /* Check if we have an early match. */
> +    for (h = haystack, n = needle; TOLOWER (*h) == TOLOWER (*n) && *h; ++h, ++n);
> +    if (*n == '\0')
> +      return (char *)haystack;
> +    if (__glibc_unlikely (*h == '\0'))
> +      return NULL;
> +    if ((size_t) (n - needle) > shift)
> +      shift = n - needle;
> +  /* Since a match may occur early on in a huge HAYSTACK, use strnlen
> +     and read ahead a few cachelines for improved performance.  */
> +    needle_len = shift + strlen (needle + shift);
> +    haystack_len = shift + __strnlen (h + shift, 256);
> +    if (__glibc_unlikely (haystack_len < needle_len))
> +      return NULL;
> +  } else {
> +    needle_len = n - needle;
> +    haystack_len = needle_len + __strnlen (haystack + needle_len, 256);
> +  }
>  
>    /* Perform the search.  Abstract memory is considered to be an array
>       of 'unsigned char' values, not an array of 'char' values.  See

-- 
Cheers,
Carlos.