Messages in this thread | | | Date | Wed, 29 Jun 2016 12:24:56 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH 1/2] lib: hexdump: use a look-up table to do hex_to_bin |
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On Thu, 30 Jun 2016 00:15:54 +0800 zengzhaoxiu@163.com wrote:
> From: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>
I have to ask, what hot paths call this where we need to add a table for optimization. And there's a chance that this wont even optimize the flow and may even slow down execution as the table will now need to be loaded into cache.
-- Steve
> > Signed-off-by: Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com> > --- > include/linux/kernel.h | 15 ++++++++++++++- > lib/hexdump.c | 36 +++++++++++++++++++----------------- > 2 files changed, 33 insertions(+), 18 deletions(-) > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > index 94aa10f..72a0432 100644 > --- a/include/linux/kernel.h > +++ b/include/linux/kernel.h > @@ -532,7 +532,20 @@ static inline char *hex_byte_pack_upper(char *buf, u8 byte) > return buf; > } > > -extern int hex_to_bin(char ch); > +extern const int8_t h2b_lut[]; > + > +/** > + * hex_to_bin - convert a hex digit to its real value > + * @ch: ascii character represents hex digit > + * > + * hex_to_bin() converts one hex digit to its actual value or -1 in case of bad > + * input. > + */ > +static inline int hex_to_bin(char ch) > +{ > + return h2b_lut[(unsigned char)ch]; > +} > + > extern int __must_check hex2bin(u8 *dst, const char *src, size_t count); > extern char *bin2hex(char *dst, const void *src, size_t count); > > diff --git a/lib/hexdump.c b/lib/hexdump.c > index 992457b..878697f 100644 > --- a/lib/hexdump.c > +++ b/lib/hexdump.c > @@ -18,23 +18,25 @@ EXPORT_SYMBOL(hex_asc); > const char hex_asc_upper[] = "0123456789ABCDEF"; > EXPORT_SYMBOL(hex_asc_upper); > > -/** > - * hex_to_bin - convert a hex digit to its real value > - * @ch: ascii character represents hex digit > - * > - * hex_to_bin() converts one hex digit to its actual value or -1 in case of bad > - * input. > - */ > -int hex_to_bin(char ch) > -{ > - if ((ch >= '0') && (ch <= '9')) > - return ch - '0'; > - ch = tolower(ch); > - if ((ch >= 'a') && (ch <= 'f')) > - return ch - 'a' + 10; > - return -1; > -} > -EXPORT_SYMBOL(hex_to_bin); > +const int8_t h2b_lut[] = { > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1, > + -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > + -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, > +}; > +EXPORT_SYMBOL(h2b_lut); > > /** > * hex2bin - convert an ascii hexadecimal string to its binary representation
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