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SubjectRe: [PATCH 2/3] lib: vsprintf: optimised put_dec() for 32-bit machines
Date
Denys Vlasenko <vda.linux@googlemail.com> writes:

> On Friday 06 August 2010 00:38, Michal Nazarewicz wrote:
>> The disadvantage is that the proposed function is 2.5-3.5 bigger.
>> Those are not big functions though -- we are talking here about
>> proposed function being below 512.

> It's a slippery slope. Here's where it ends: glibc
> has memcpy() function which is "only" 8k of code or so.
> I'm not joking.

I'm aware of that. I assume that someone more clever then me will
decide whether to accept this patch or not. (Also we win a few bytes on
put_dec_full() and put_dec_8bit()). :P

>> +#if BITS_PER_LONG == 64
>> +
> ...
>> +#else
> ...
>> +/*
>> + * Based on code by Douglas W. Jones found at
>> + * <http://www.cs.uiowa.edu/~jones/bcd/decimal.html#sixtyfour>. This
>> + * performs no 64-bit division and hence should be faster on 32-bit
>> + * machines then the version of the function above.
>> + */
>> +static noinline_for_stack
>> +char *put_dec(char *buf, unsigned long long n)
>> +{
>> + uint32_t d3, d2, d1, q;
>> +
>> + if (!n) {
>> + *buf++ = '0';
>> + return buf;
>> + }
>> +
>> + d1 = (n >> 16) & 0xFFFF;
>> + d2 = (n >> 32) & 0xFFFF;
>> + d3 = (n >> 48) & 0xFFFF;
>
> Are you assuming that sizeof(long long) == 8, always?

Well... yes. C requires long long to be at least 64-bit and I don't
see it being larger in any foreseeable feature. Wouldn't it be enough
to put a static assert here?

--
Best regards, _ _
.o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michal "mina86" Nazarewicz (o o)
ooo +--<mina86-tlen.pl>--<jid:mina86-jabber.org>--ooO--(_)--Ooo--

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