ah....I think the number of significant digits for a float is 24 bits
so the cast may be rounding. See:
http://en.wikipedia.org/wiki/Floating_point#Rounding_modes
MS
Geo Gkolfin wrote:
> There are not so many steps to be made. The functionality is described
> in my first mail.
>
>
> On Fri, Aug 19, 2011 at 9:38 PM, Eric Decker <cire...@gmail.com
> <mailto:cire...@gmail.com>> wrote:
>
>
>
> On Fri, Aug 19, 2011 at 11:32 AM, Geo Gkolfin <geo198...@gmail.com
> <mailto:geo198...@gmail.com>> wrote:
>
> Thanks for your answer!
> Actually it almost worked!
> %lu prints 3354000128 instead of 3354000112.
> %lx prints c7e9fb00 which is 3354000128 hex.
> This can drive you crazy! Any ideas please?
>
>
> Without explicitly stepping through the code and seeing what it is
> doing, we would be guessing.
>
>
> On Thu, Aug 18, 2011 at 12:58 AM, Michael Schippling
> <sc...@santafe.edu <mailto:sc...@santafe.edu>> wrote:
>
> That is a little odd...
>
> I guess the implicit casting is trying to help you by
> returning the largest value for the uint16 when converting
> from a too-big float. When you change to uint32 you
> should get 0xC7E9FAF0 in your integer (which is what
> my Widows calculator shows as the correct conversion
> for decimal 354000112). Then, because the top bit is
> set and you asked for a signed decimal output "%ld"
> you should get a negative value, but it's off by 16...
> -940967168d == 0xC7E9FB00
> so I'm not sure what is going on.
>
> Try printing %lu or %lx and see what you get.
>
> MS
>
> Geo Gkolfin wrote:
>
> Hello!
>
> I am using telosb motes and tinyos-2.1.0. I have an
> application in which some floating point operations are
> done and I wish to print (using PrintfClient) only the
> decimal part of the result. Since the printed value is
> not what it should be -it is always 65535- I wrote a
> simple program where I have:
>
> float y;
> uint16_t x;
>
> y=4354.542134509;
> x=y;
> printf("int(4354.542134509)=%__u\n",x);
> printfflush();
>
> I run
> java net.tinyos.tools.PrintfClient -comm
> serial@/dev/ttyUSB0:telosb
>
> and I get the 4354!
>
> If I change the value stored in y to:
> y=3354000112.542134509 then the printf returns 65535
> -the same value as in my application! So I guess this
> is because the value does not "fit" into a uint16_t. I
> change x definition to uint32_t and %u to %ld (make is
> okay with that), but then the printed value is -940967168!
> What is the problem?
>
> Thanks in advance,
> Georgia
>
>
>
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> --
> Eric B. Decker
> Senior (over 50 :-) Researcher
>
>
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