[avr-libc-dev] avr-libc: optimization for ltoa/printf

[Dmitry E. Oboukhov]

Hi, There!

Now avr-libc uses division cycles when it converts number to string.

Benchmarks page (http://www.nongnu.org/avr-libc/user-manual/benchmarks.html)
says that ltoa (12345L, s, 10) requires 3174 - 3136 cycles for the
conversions.

If we use the other algorithm, we can reduce the time more than three
times.

in attache I placed a test-file that contains 'my_ultoa' function.

my_ultoa(12345L, s, 10)  requires 924 MCU cycles.
    against ultoa(12345L, s, 10) - 3174

But that algorithm can be realized only for some radixes, so the
function can be used if one of realized radixes is in third argument.

Also function __ultoa_invert can use the algorithm (it is called from
*printf), so using the algorithm we can spend less time then current
variant.

The algorithm can be realized for uint, it will more fast.

Sometimes conversion time is very important (for example if we realize
some text network protocols) so I think that algorithm can be used in
functions ltoa/itoa/*printf :)

What do You think about this algorithm?


PS: sorry for my bad English
-- 

. ''`.                               Dmitry E. Oboukhov
: :’  :   email: address@hidden jabber://address@hidden
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