Messages in this thread | | | From | Denys Vlasenko <> | Subject | Re: [PATCHv2 1/3] lib: vsprintf: optimised put_dec_trunc() and put_dec_full() | Date | Tue, 10 Aug 2010 05:17:48 +0200 |
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On Sunday 08 August 2010 21:29, Michal Nazarewicz wrote: > -- Speed -------------------------------------------------------- > orig_put_dec_full : 1.054570 1.356214 1.732636 1.725760 Original > mod1_put_dec_full : 1.000000 1.017216 1.255518 1.116559 > mod3_put_dec_full : 1.018222 1.000000 1.000000 1.000000 Proposed > > orig_put_dec_trunc : 1.137903 1.216017 1.850478 1.662370 Original > mod1_put_dec_trunc : 1.000000 1.078154 1.355635 1.400637 > mod3_put_dec_trunc : 1.025989 1.000000 1.000000 1.000000 Proposed > -- Size --------------------------------------------------------- > orig_put_dec_full : 1.212766 1.310345 1.355372 1.355372 Original > mod1_put_dec_full : 1.021277 1.000000 1.000000 1.000000 > mod3_put_dec_full : 1.000000 1.172414 1.049587 1.049587 Proposed > > orig_put_dec_trunc : 1.363636 1.317365 1.784000 1.784000 Original > mod1_put_dec_trunc : 1.181818 1.275449 1.400000 1.400000 > mod3_put_dec_trunc : 1.000000 1.000000 1.000000 1.000000 Proposed
In my testing on Phenom II the speed gain is smaller, but it is indeed faster. And smaller!
> + /* > + * '(x * 0xcccd) >> 19' is an approximation of 'x / 10' that > + * gives correct results for all x < 81920. However, because > + * intermediate result can be at most 32-bit we limit x to be > + * 16-bit. > + * > + * Because of those, we check if we are dealing with a "big" > + * number and if so, we make it smaller remembering to add to > + * the most significant digit. > + */ > + if (q >= 50000) { > + a = '5'; > + q -= 50000; ... > + /* > + * We need to check if q is < 65536 so we might as well check
You meant "need to check if q is < 81920"?
> + * if we can just call the _full version of this function. > + */ > + if (q > 9999) > + return put_dec_full(buf, q);
-- vda
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