Re: [avr-libc-dev] 64-bit doubles

[Preston Wilson]

"Dave N6NZ" wrote:

> Ron Kreymborg wrote:
>>> -----Original Message-----
>>> From: Weddington, Eric [mailto:address@hidden
>>> Sent: Sunday, 21 December 2008 6:00 AM
>>> To: Ron Kreymborg; address@hidden
>>> Subject: RE: [avr-libc-dev] 64-bit doubles
>>> 
>>> 
>>> 
>>>> -----Original Message-----
>>>> From:
>>>> address@hidden
>>>> [mailto:address@hidden
>>>> org] On Behalf Of Ron Kreymborg
>>>> Sent: Saturday, December 20, 2008 5:03 AM
>>>> To: address@hidden
>>>> Subject: [avr-libc-dev] 64-bit doubles
>>>> 
>>>> A quick look at AVR Libc for 20081205 still lists doubles as
>>>> only 32-bit. Is
>>>> this so? If yes does anyone know of a 64-bit double library?
>>>> I am pointing
>>>> heliostats and 32-bits are just not enough.
>>>> 
>>>> Ron
>>> Hi Ron,
>>> 
>>> Yes, that is correct. Floats and doubles are 32-bits. No, I don't know
>>> of a library. We (the avr-libc developers) have been advertising for
>>> volunteers to help put together 64-bit double support for quite some
>>> time. Nobody has volunteered yet.
>>> 
>>> Eric Weddington
>> 
>> Ok. For this project my good sense is saying go to a mcf52xx or M16C and a
>> commercial compiler, but I have written fp code for now ancient processors
>> and used the CORDIC transformations for transcendentals, so I'll have a look
>> at AVRs over the xmas break. No promises...
>> 
>> Ron
>> 
> Is support for 64 bit double limited only by availability of a math
> library?  I would expect that 8-byte variables, register allocations,
> etc, would also be an issue, since avr-gcc doesn't have anything bigger
> than a 32-bit long or 32-bit float right now.
> 
> Isn't there some compiler infrastructure that would have to happen also?

avr-gcc does support 64-bit integers (signed long long int, and unsigned
long long int), and there is nothing to stop someone from writing a library
that uses their own 64-bit float type without making changes to the
compiler.  You would not be able to use the built in double type for 64-bit
floats without making changes to the compiler itself.

-Preston