Re: [PATCH][RFC] Avoid table lookup in isascii, isxdigit.

["Carlos O'Donell" <carlos at redhat dot com>]

On 04/09/2013 07:57 AM, OndÅej BÃlka wrote:
> Hi, I looked to ctype and thougth if it is possible to decrease table
> size to 512 bytes. I did not succeed but made following three
> optimizations.
> 
> 1. In isdigit use & instead &&. Gcc contains bug that optimizes first
> but not second case.
> 2. Refactor isdigit macro
> 3. Write isxdigit and isascii.

You should add a microbenchmark for isdigit, isascii, and isxdigit :-)
 
> Following code is enclosed in
> 
> #ifndef _ISOMAC
> # if !defined __NO_CTYPE && !defined NOT_IN_libc

If we are not testing for ISO C compliance, and
we are not building ctype.c or ctype_l.c, and we
are building libc...

> Is there reason why we cannot also transform user code in this way?

User code must consult LC_CTYPE to get this correct?

> ---
>  include/ctype.h |   23 ++++++++++++++++++++---
>  1 files changed, 20 insertions(+), 3 deletions(-)
> 
> diff --git a/include/ctype.h b/include/ctype.h
> index 6a18039..7f9e928 100644
> --- a/include/ctype.h
> +++ b/include/ctype.h
> @@ -56,11 +56,28 @@ __ctype_tolower_loc (void)
>  /* The spec says that isdigit must only match the decimal digits.  We
>     can check this without a memory access.  */
>  #  undef isdigit
> -#  define isdigit(c) ({ int __c = (c); __c >= '0' && __c <= '9'; })
> +#  define isdigit(c) ({ int __c = (c); (__c >= '0') & (__c <= '9'); })
>  #  undef isdigit_l
> -#  define isdigit_l(c, l) ({ int __c = (c); __c >= '0' && __c <= '9'; })
> +#  define isdigit_l(c, l) isdigit(c)
>  #  undef __isdigit_l
> -#  define __isdigit_l(c, l) ({ int __c = (c); __c >= '0' && __c <= '9'; })
> +#  define __isdigit_l(c, l) isdigit(c)
> +
> +/* The spec says that isxdigit must only match the hexadecimal digits.  We
> +   can check this without a memory access.  */
> +#  undef isxdigit
> +#  define isxdigit(c) ({ int __c = (c); ((__c >= '0') & (__c <= '9')) || ((__c >= 'a') & (__c <= 'f')) || ((__c >= 'A') & (__c <= 'F')); })
> +#  undef isxdigit_l
> +#  define isxdigit_l(c, l) isxdigit(c)
> +#  undef __isxdigit_l
> +#  define __isxdigit_l(c, l) isxdigit(c)
> +
> +#  undef isascii
> +#  define isascii(c) ({ int __c = (c); (__c & 128 == 0); })
> +#  undef isascii_l
> +#  define isascii_l(c, l) isascii(c)
> +#  undef __isascii_l
> +#  define __isascii_l(c, l) isascii(c)
> +
>  # endif
>  #endif
>  
> 

Cheers,
Carlos.