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Re: cyg_ticks_to_timespec()
- To: "Boris V. Guzhov" <borg at int dot spb dot ru>
- Subject: Re: [ECOS] cyg_ticks_to_timespec()
- From: Jonathan Larmour <jlarmour at redhat dot com>
- Date: Wed, 18 Apr 2001 20:43:56 +0100
- Cc: ecos-discuss at sourceware dot cygnus dot com, Hugo Tyson <hmt at redhat dot com>
- Organization: Red Hat UK Ltd.
- References: <003701c0c7dc$c95976f0$7601a8c0@borg>
"Boris V. Guzhov" wrote:
>
> Hi,
> I use elix ecos configuration. In the
> packages/compat/posix/current/src/time.cxx file
> there is a cyg_ticks_to_timespec() function. I think that in the function
> there is a bug.
> For example: for ticks=454 the function should calculate tv_sec=4
> tv_nsec=0.54e9,
> but it calculate tv_sec=5 tv_nsec=3834967296.
You're right. Out of interest, if you interpret tv_nsec as a signed rather
than unsigned long it comes out as -460000000 which is a more interesting
value. i.e. it is negative.
Hugo, the code for cyg_ticks_to_timespec() just uses your scary clock
convertors. The convertor is:
(gdb) p sec_inverter
$1 = {mul1 = 1, div1 = 100, mul2 = 1, div2 = 1}
and the conversion is:
cyg_uint64 t = (cyg_uint64)value;
// Do this in an order to prevent overflow at the expense of
// accuracy:
t *= pcc->mul1;
t += pcc->div1 / 2;
t /= pcc->div1;
t *= pcc->mul2;
t += pcc->div2 / 2;
t /= pcc->div2;
// The alternative would be to do the 2 multiplies first
// for smaller arguments.
return (cyg_tick_count)t;
So it seems that rounding off is intentional. In which case I should just
tweak cyg_ticks_to_timespec to fix up the value if tv_nsec is negative.
Before I do it, I just want to check my understanding that the convertors
are doing the right thing by rounding not truncating.
Jifl
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