Am 17.06.2015 um 00:51 schrieb Orestes Leal Rodriguez: >> Use the force^Wcheckpatch.pl. > This is the output of checkpatch.pl: > output of checkpatch: total: 0 errors, 0 warnings, 42 lines checked > /root/string.c.patch has no obvious style problems and is ready for submission
But it does not apply at all. Did you test it? I fear your mail client did some whitespace damage. >> You need to explain that in the commit message, my young padawan. > Very small update to strlen and strnlen that now use less cpu instructions by > using a counter to avoid memory address > arithmetic, which cause that the compiler adds more machine > instructions for computing the length of the string just before > returning from the functions, the old machine code is like the > following: > > mov -0x4(%ebp),%edx > mov 0x8(%ebp),%eax > sub %eax,%edx > mov %edx,%eax > leave > ret > > > now in the new versions the value is not calculated anymore, > instead he value of the counter is put on eax after the > condition inside the loop no longer holds, and then return: > > mov -0x4(%ebp),%eax > leave > ret > > With this a few cpu instructions are saved. x86_32 does not matter here as we have already an optimized strlen() in arch/x86/lib/string_32.c. Did you check whether the optimization is worth on other archs? Hint: grep __HAVE_ARCH_STRLEN > > Signed-off-by: Orestes Leal Rodriguez <[email protected]> > --- > > Signed-off-by: Orestes Leal Rodriguez <[email protected]> What does this 2nd SoB here? > diff --git a/lib/string.c b/lib/string.c > index 992bf30..c873436 100644 > --- a/lib/string.c > +++ b/lib/string.c > @@ -17,6 +17,10 @@ > * * Sat Feb 09 2002, Jason Thomas <[email protected]>, > * Matthew Hawkins <[email protected]> > * - Kissed strtok() goodbye > + * > + * * Tuesday June 16 2015, Orestes Leal Rodriguez <[email protected]> > + * - strlen, strnlen: by using a single counter we use less cpu instructions > + * by avoiding substracting the memory addresses before return No need to add anything here. These days we have git. :-) > */ > > #include <linux/types.h> > @@ -401,11 +405,11 @@ EXPORT_SYMBOL(strim); > */ > size_t strlen(const char *s) > { > - const char *sc; > + size_t sz = 0; > > - for (sc = s; *sc != '\0'; ++sc) > - /* nothing */; > - return sc - s; > + for (; *s++ != '\0'; sz++) > + /* empty */; <nitpick> Why suddenly "empty" instead of "nothing"? </nitpick> > + return sz; > } > EXPORT_SYMBOL(strlen); > #endif > @@ -418,12 +422,13 @@ EXPORT_SYMBOL(strlen); > */ > size_t strnlen(const char *s, size_t count) > { > - const char *sc; > + size_t sz = 0; > > - for (sc = s; count-- && *sc != '\0'; ++sc) > - /* nothing */; > - return sc - s; > + for (; count-- && *s++ != '\0'; sz++) > + /* empty */; Same here. Thanks, //R2D2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
