Jim Meyering wrote:
> To have any hope of sanity/reproducibility in different locales,
> this function must return the same result, regardless of the current
> locale settings.
Yes. In the opposite case, if the function was to handle non-ASCII letters
like ASCII letters, it should also have a codepath for multibyte locales.
> I suggest using this macro in place of ISDIGIT:
>
> #define ISDIGIT(c) ((unsigned int) (c) - '0' <= 9)
This is equivalent to the c_isdigit macro from "c-ctype.h", assuming the
normal compiler optimizations. gcc yields identical code for ISDIGIT as for
c_isdigit.
Bruno
=============================== foo.c ================================
int isdigit1 (const char *s)
{
return
({ int __c = (*s);
(__c >= '0' && __c <= '9');
});
}
int isdigit2 (const char *s)
{
return ((unsigned int) (*s) - '0' <= 9);
}
=========================== gcc -O2 -S foo.c ==========================
.file "foo.c"
.text
.p2align 4,,15
.globl isdigit1
.type isdigit1, @function
isdigit1:
pushl %ebp
movl %esp, %ebp
movl 8(%ebp), %eax
popl %ebp
movsbl (%eax),%eax
subl $48, %eax
cmpl $9, %eax
setbe %al
andl $255, %eax
ret
.size isdigit1, .-isdigit1
.p2align 4,,15
.globl isdigit2
.type isdigit2, @function
isdigit2:
pushl %ebp
movl %esp, %ebp
movl 8(%ebp), %eax
popl %ebp
movsbl (%eax),%eax
subl $48, %eax
cmpl $9, %eax
setbe %al
andl $255, %eax
ret
.size isdigit2, .-isdigit2
.ident "GCC: (GNU) 3.3.1 (SuSE Linux)"
