Re: [PATCH] strcasestr: check if ne[0] is in hs with strchr or strpbrk as does strstr

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 14/10/23 05:32, James Tirta Halim wrote:
> ---
>  string/strcasestr.c | 31 +++++++++++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
> 
> diff --git a/string/strcasestr.c b/string/strcasestr.c
> index 2f6b4f8641..aca41211dd 100644
> --- a/string/strcasestr.c
> +++ b/string/strcasestr.c
> @@ -55,6 +55,30 @@
>  #endif
>  
>  
> +static inline char *__attribute__ ((always_inline))
> +strcasechr (const char *s, char c)
> +{
> +  if (isalpha(c)) {
> +    /* May have optimized strcspn? */
> +#if defined __sparc__ || defined __sparc || defined __x86_64__ || defined _M_X64 || defined __s390x__ || defined i386 || defined __i386__ || defined __i386 || defined _M_IX86 || defined __PPC64__ || defined __ppc64__ || defined _ARCH_PPC64 || _ARCH_PWR8
> +    const char a[] = {tolower(c), toupper(c), '\0'};

We have the sysdep folder exactly to provide such macros if requires, for instance
the file sysdeps/generic/string-fzi.h.

So if this optimization is really worth, the best way to provide would be through
a generic implementation like:

  static __always_inline char *
  strcasechr (const char *s, char c)
  {
    /* Generic implementation.  */
  }

And then on each architecture where using strcspn is better to add a string-xxx.h
override.

> +    s = (char *)strcspn(s, a);
> +#else
> +    c = tolower(c);
> +    while (*s && tolower(*s) != c)
> +      ++s;
> +#endif
> +    if (*s != '\0')
> +      return (char *)s;
> +  } else {
> +    s = strchr(s, c);
> +    if (s != NULL)
> +      return (char *)s;
> +  }
> +  return NULL;
> +}
> +
> +
>  /* Find the first occurrence of NEEDLE in HAYSTACK, using
>     case-insensitive comparison.  This function gives unspecified
>     results in multibyte locales.  */
> @@ -68,6 +92,10 @@ STRCASESTR (const char *haystack, const char *needle)
>    if (needle[0] == '\0')
>      return (char *) haystack;
>  
> +  haystack = strcasechr (haystack, *needle);
> +  if (haystack == NULL || needle[1] == '\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.  */
> @@ -75,6 +103,9 @@ STRCASESTR (const char *haystack, const char *needle)
>    haystack_len = __strnlen (haystack, needle_len + 256);
>    if (haystack_len < needle_len)
>      return NULL;
> +  
> +  if (strncasecmp (haystack, needle, needle_len) == 0)
> +    return (char *) haystack;
>  
>    /* Perform the search.  Abstract memory is considered to be an array
>       of 'unsigned char' values, not an array of 'char' values.  See