RE: [avr-gcc-list] Optimizing a 16-bit * 8-bit -> 24-bit multiplication

[Eric Weddington]

Hi Shaun,

Please add this to a Patch Tracker in the avr-libc project page on Savannah.
Emails have a tendency to get lost and I wouldn't want this to be forgotten.

Eric Weddington 

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of Shaun Jackman
> Sent: Wednesday, December 06, 2006 11:26 AM
> To: Galen Seitz
> Cc: address@hidden
> Subject: Re: [avr-gcc-list] Optimizing a 16-bit * 8-bit -> 
> 24-bit multiplication
> 
> On 12/1/06, Galen Seitz <address@hidden> wrote:
> > Not exactly what you want, but this might help you get started.
> >
> > galen
> >
> >
> > extern inline int16_t
> > mult_s16_u8s16(uint8_t a, int16_t b)
> ...
> 
> Thanks for the code snippet, Galen. Using your mult_s16_u8s16 for
> inspiration, I wrote mul_16_8 (u16 * u8 -> u24). Perhaps these
> functions should be added to avr-libc.
> 
> Cheers,
> Shaun
> 
> static inline uint32_t mul_16_8(uint16_t a, uint8_t b)
> {
>       uint32_t product;
>       asm (
>               "mul %A1, %2\n\t"
>               "movw %A0, r0\n\t"
>               "clr %C0\n\t"
>               "clr %D0\n\t"
>               "mul %B1, %2\n\t"
>               "add %B0, r0\n\t"
>               "adc %C0, r1\n\t"
>               "clr r1"
>               : "=&r" (product)
>               : "r" (a), "r" (b));
>       return product;
> }
> 
> 
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