[Sound-open-firmware] [PATCH 2/4] Tone: Add channel specific volume plus other fixes

[Liam Girdwood]

On Thu, 2017-06-22 at 15:22 +0300, Seppo Ingalsuo wrote:
> > Thanks, that works. At least with the compiler that I use 
> > (http://alsa-project.org/main/index.php/Firmware) the optimizing
> does 
> > the conversion to fixed without increase of the firmware image size.
> I 
> > also checked from disassembly that this part of the code remains 
> > identical. I did a minor fix and added rounding into the macro
> since 
> > compiler doesn't round the cast to int:
> >
> > #define TONE_FREQ(f)    (int)((f) * (1 << 16))    /* f = float */
> >
> > #define TONE_FREQ(f)    (((int)((f) * (1 << 17)) + 1) >> 1)  /* f = 
> > float */
> 
> Sorry, the rounded version overflows and depending on the way 20000
> vs. 
> 20000.0 as the parameter the compiler may even pass it silently.
> However 
> this way the rounded Q16.16 conversion seems to work:
> 
> #define TONE_FREQ(f) (int)(((int64_t)((f) * 131072.0 + 1.0)) >> 1) /*
> f 
> = float */

Best to make 131072.0 a macro too so easy to understand what it's doing.

We should also have this as our non optimal "generic" version and we
should look to create arch specific macros (with inline assembler) later
on (that take take of overflow or larger types).

Liam

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