On 7/3/20 4:58 AM, Jody Bruchon wrote:
>
>
> On July 2, 2020 3:26:29 PM EDT, Tito <[email protected]> wrote:
>> hi,
>> just for fun I add my version:
>>
>> char* FAST_FUNC last_char_is(const char *s, int c) {
>> while (s && *s && *(s + 1)) s++;
>> return (c == *s) ? (char *)s : NULL;
>> }
>
> That's pretty small, but it performs three comparisons for each character
> until
the end and effectively scans the string twice in "parallel." If a bad pointer
is passed in s, it'll segfault at the equality check in the return statement
even though the first comparison is supposed to be a null pointer safeguard.
Hi,
Ops that slipped through, my copy-paste test case was wrong:
c = last_char_is("NULL", 'e');
Improved version:
char* last_char_is(const char *s, int c) {
if (!s || !*s) return NULL;
while (*(s + 1))s++;
return (c == *s) ? (char *)s : NULL;
}
or if you like gotos:
char* FAST_FUNC last_char_is(const char *s, int c)
{
if (!s || !*s) goto OUT;
while (*(s + 1))s++;
if (c == *s) return (char *) s;
OUT:
return NULL;
}
bloatcheck is same for both:
function old new delta
last_char_is 53 42 -11
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-11) Total: -11 bytes
text data bss dec hex filename
980860 16891 1872 999623 f40c7 busybox_old
980849 16891 1872 999612 f40bc busybox_unstripped
Ciao,
Tito
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