[ECOS] libm on SH7750.

[Jonathan Larmour]

ryosuke-tajima@mosk.tytlabs.co.jp wrote:
> Hi, all. Thanks for very useful advice in this mailing list, and now I
> have another problem.
> 
> I want to use math library on SH7750 system. I cannot get correct
> result from some math function (sin, cos, and sqrt) in my program. The
> result of multiply, division, plus and minus operation for floating
> value is correct.
> 
> The sh-elf-gcc has several switch for floating operation, then, I
> tried some math tests in eCos package with gcc switch -m4, -m4-single,
> -m4-single-only.  Result was:
> 
> 
> -m4:	     
> 	     sqrt.c:		passed.
> 	     cos.c, sin.c:	hang up.
> 
> -m4-single:  
> 	     sqrt.c:		passed.
> 	     cos.c, sin.c:	torelance error.
> 
> -m4-single-only:  
>              Cannot compile because of an error "IEEE-style 64-bit
>              doubles are required to use the math library"
> 
> How can I use math library on SH4? Had anyone made these function work
> correctly?

Given your follow up message, then I assume you have a hardware FPU. 
Taking a brief look at the GCC docs, it appears that the correct setting 
of -m4 versus -m4-single is a property of whether the FPU has been set up 
in single or double precision mode by default. You should find out which 
of these is the case.

The fact that -m4-single at least doesn't hang is _something_ in its 
favour. The fact it gets a tolerance error may not necessarily mean 
there's a problem - the maths tests only work by checking if a returned 
value is withing an acceptable tolerance. It's possible that that in 
single precision mode, the results are not quite accurate enough and hence 
the tests fail. That's a good line of inquiry for you to check anyway.

Jifl
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