Arithmetic on aggregated types

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Hi forum,

does anyone know of a resource covering arithmetic on aggregated types?

I'm using addition like this:

C

typedef struct
{
    uint8_t hb;
    uint8_t mb;
    uint8_t lb;
}BunchOBytes;

BunchOBytes Add(BunchOBytes in0, BuncOBytes in1)
{
    BunchOBytes result;
    uint16_t sum;

    sum = in0.lb + in1.lb;
    result.lb = sum;
    sum >>= 8;
    sum += in0.mb + in1.mb;
    result.mb = sum;
    sum >>= 8;
    sum += in0.hb + in0.hb;
    result.hb = sum;

    return(result); // handle overflow
}

Now I'm in need of division by a scalar. Can anyone recommend a book on this?

Posted 26-Nov-15 3:03am

lukeer

Updated 26-Nov-15 20:40pm

v2

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Philippe Mori 26-Nov-15 12:20pm

In addition to Solution 1, that code does not make much sense as an unsigned is typically 32 bits and your addition works on 24 bits...

lukeer 27-Nov-15 2:42am

Corrected that. I forgot to mention that this is not for .NET or even PC but an embedded device. I changed the data type within the struct to clearly state what size it is.

CPallini 27-Nov-15 2:59am

What is your requirement, exactly? Doesn't your system provide, for instance, the division operation on 24 (possibly 32) bit integers? Depending on your needs, you might also find assembly better suited for this.

lukeer 30-Nov-15 3:20am

The requirement has gone academic during wednesday afternoon (and, in fact, evening) due to some changes to pre- and post-scaler settings. With this new setup, 24 bits are indeed enough and the compiler takes care of all the fiddling with 8 bit registers.

But who knows? Some time an 8-bit device will have to calculate on something larger than 32 bits. So I'm still interrested in algorithms adding and multiplying arbitrary amounts of chars to one another.

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Jochen Arndt · Answer 1 · 2015-11-26T03:13:00

Solution 1

It seems that you don't want to use an enum but a structure:

C++

typedef struct
{
    unsigned hb;
    unsigned mb;
    unsigned lb;
}BunchOBytes;

Posted 26-Nov-15 3:13am

Jochen Arndt

Comments

lukeer 27-Nov-15 2:43am

Yes, of course. Thanks for pointing that out and have a 5.
Any hint on the actual question?

Jochen Arndt 27-Nov-15 3:43am

You may have a look at this link: http://www.bearcave.com/software/divide.htm
I have done similar so far only using assembly on Microchip processors. For those and other processors there are libraries with sources.

If your C compiler supports 32-bit integers and speed is not too important, I would just let the compiler do the work as already suggested by CPallini.

lukeer 30-Nov-15 3:24am

Thank you, that's exactly the type of stuff I was looking for.