Re: [avr-libc-dev] Pow Function in avr8

[Georg-Johann Lay]

Jan Waclawek schrieb:
> > Floating point equivalence is not guaranteed so is this comparison
> > valid ?
>
> C99 in 5.2.4.2.2#5 says: The accuracy ofthe floating-point operations
> (+, -, *, /) and of the library functions in <math.h>and <complex.h>
> that return floating-point results is implementation-defined [...]
> The implementation may state that the accuracy is unknown.

Which is the case, cf. [1]:

> > * The accuracy of the floating-point operations and of the library
> >   functions in <math.h> and <complex.h> that return floating-point
> >   results (C90 and C99 5.2.4.2.2).
> >
> >   The accuracy is unknown.

Which basically means precision is a matter of the target.
The (E)ABI of avr-gcc does not define floating point precision,
at least I don't know of it.  Similar for AVR Libc.

> PS. Are you sure you linked against avr-libc's math library?

FYI and in the case you refer to whether -lm is used or not:
That won't matter in new avr-gcc, cf. [2]

Johann


[1]
http://gcc.gnu.org/onlinedocs/gcc/Floating-point-implementation.html

[2]
http://gcc.gnu.org/PR54461