Re: [avr-gcc-list] 24 bits (u)ints

[Georg-Johann Lay]

On 30.11.2016 08:40, Diogo Martins Silva wrote:
> Hello all.
>
> The avr-gcc wiki (https://gcc.gnu.org/wiki/avr-gcc) lists 24 bits
> (u)ints as an extension since version 4.7. How do I use them?
>
> Thanks
>
> Diogo

You can use it basically like any other integer type, for example:


__uint24 mul24 (unsigned char a, unsigned int b)
{
    return (__uint24) a * b;
}

__int24 get_val24 (const __flash __int24 vals[], unsigned char pos)
{
    return vals[pos];
}

For a MCU with MUL, this gives

mul24:
        mul r24,r22
        movw r18,r0
        mul r24,r23
        add r19,r0
        mov r20,r1
        clr __zero_reg__
        adc r20,__zero_reg__
        mov r24,r20
        movw r22,r18
        ret

get_val24:
        ldi r18,lo8(3)
        mul r22,r18
        add r24,r0
        adc r25,r1
        clr __zero_reg__
        movw r30,r24
        lpm r22,Z+
        lpm r23,Z+
        lpm r24,Z
        ret

When you are passing a 24-bit value to a variadic function like printf, 
you have to cast it to (un)signed long by hand; avr-gcc does not 
automatically promote such types to 32-bit types.  printf et al. have no 
format specifiers for 24-bit types.

Johann