[FFmpeg-user] compiling for android

[Carl Eugen Hoyos]

Nicolas George <george <at> nsup.org> writes:

> Le primidi 21 messidor, an CCXXII, Patrick Shirkey a écrit :
> > Unfortunately all these flags not working for me. 
> > Does that suggest a problem (in this case) with the 
> > compiler or ffmpeg?
> 
> You can try to compile the following simple code:

Thank you for the more useful test case!

> #include <math.h>
> 
> double test(double x)
> {
>     return cos(x) + sin(x);
> }
> 
> If the compiler from the Android NDK issues code 
> using sincos, then it is broken, since the platform 
> does not provide it.

Which appears not to be unusual on Android.

The complete test case:
$ cat test.c
#define _GNU_SOURCE
#include <math.h>

double sc(double a)
{
return sin(a) + cos(a);
}
$ gcc test.c -c && nm test.o
                 U cos
0000000000000000 T sc
                 U sin
$ gcc test.c -c -O1 && nm test.o
0000000000000000 T sc
                 U sincos
$ gcc test.c -c -O1 -fno-builtin-sin && nm test.o
                 U cos
0000000000000000 T sc
                 U sin
$ gcc test.c -c -O1 -fno-builtin-cos && nm test.o
                 U cos
0000000000000000 T sc
                 U sin

I believe the toolchain is broken if it produces a 
sincos symbol although you compiled with -fno-builtin.

(-fno-builtin-sincos has NO effect.)

The define is not needed but maybe it makes the 
compiler believe that sincos() is available?

Carl Eugen