Re: test failure for mappers.cc

[Ben Abbott]

On Nov 10, 2010, at 2:23 PM, John W. Eaton wrote:

> On 10-Nov-2010, Ben Abbott wrote:
> 
> | If you (anyone?) can tell me which library is responsible I'll take
> | a look at Apple's changes to the gcc sources. If I can find the
> | place to go, I'll file a bug report as well.
> 
> The atan2f function should be in libm.  What happens if you compile
> and run the following C program on your system?  I see the following
> results on mine:
> 
>  M_PI = 3.141592741012573
>  (float) M_PI = 3.1415927 (0x40490fdb)
>  atan2f (0.0f, -1.0f) = 3.14159274 (0x40490fdb)
>  atan2f (0.0f, -1.0f) - (float) M_PI = 0.00000000 (0x00000000)
> 
> But it looks like there are special cases in the libc atan2 function
> (in the file sysdeps/ieee754/flt-32/e_atan2f.c):
> 
>  tiny  = 1.0e-30,
>  ...
>  pi      = 3.1415927410e+00,  /* 0x40490fdb */
>  ...
>      /* when y = 0 */
>          if(iy==0) {
>              switch(m) {
>                  case 0:
>                  case 1: return y;       /* atan(+-0,+anything)=+-0 */
>                  case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
>                  case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
>              }
>          }
> 
> Both tiny and pi are declared as float in this function.
> 
> jwe

I get the following

M_PI = 3.141592741012573
(float) M_PI = 3.1415927 (0x40490fdb)
atan2f (0.0f, -1.0f) = 3.14159250 (0x40490fda)
atan2f (0.0f, -1.0f) - (float) M_PI = -0.00000024 (0xb4800000)

Looking through Apple's sources, I don't see a atan2f.c. But I do see atan2f.s 
...

        
http://www.opensource.apple.com/source/Libm/Libm-315/Source/Intel/atan2f.s

Ben