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From: Andrew on 23 Sep 2009 15:48
I'm using CodeVision C compiler on an AVR.
CodeVision has 32bit limitation for integers.
I need to do 64bit integer math (32bx32b, 32b+32b).

I could reinvent the wheel,
but figure this has to be out there
in multiple places for free.

Any suggestions for free
C source for 64bit integer math?


From: Arlet on 24 Sep 2009 01:48
On Sep 23, 9:48 pm, Andrew <asm...(a)blackstone.biz> wrote:
> I'm using CodeVision C compiler on an AVR.
> CodeVision has 32bit limitation for integers.
> I need to do 64bit integer math (32bx32b, 32b+32b).
>
> I could reinvent the wheel,
> but figure this has to be out there
> in multiple places for free.
>
> Any suggestions for free
> C source for 64bit integer math?

This is usually easier done in assembler, where you have access to the
carry flag. You could look at the generated assembler code for 32 bit
math, and extend it for 64 bit.

Or you could use a compiler that supports the "long long" type, such
as gcc.
From: Jon Kirwan on 25 Sep 2009 04:58
On Wed, 23 Sep 2009 12:48:23 -0700, Andrew <asmith(a)blackstone.biz>
wrote:

>I'm using CodeVision C compiler on an AVR.
>CodeVision has 32bit limitation for integers.
>I need to do 64bit integer math (32bx32b, 32b+32b).
>
>I could reinvent the wheel,
>but figure this has to be out there
>in multiple places for free.
>
>Any suggestions for free
>C source for 64bit integer math?

Looks like you already posted this up on avrfreaks and got some
replies. I didn't really understand your 32b+32b request, as that
requires only 33 bits -- only one bit is valid in the upper 32-bit
word of a 64-bit result for unsigned, if that's what you wanted. It's
not hard to generate for unsigned, but slightly more trouble for
signed. Also, you didn't specify signed vs unsigned or whether you'd
like to mix the two types, which compounds the problem of providing
any useful answer. And you didn't address speed or code size. I
gather you want this entirely in c, though, and don't want anything
more than multiplication and addition operations?

Tell us where you are now and fill in some more details, if you don't
already have a solution from posting elsewhere. Might be a better
shot at an answer here, then.

Jon

P.S. If you are looking for generalized code in c, there is a book I
might point you towards which gets right down into the details of a
fairly general purpose, expandable set of routines entirely in c.
From: Nobody on 25 Sep 2009 15:30
On Wed, 23 Sep 2009 12:48:23 -0700, Andrew wrote:

> I'm using CodeVision C compiler on an AVR.
> CodeVision has 32bit limitation for integers.
> I need to do 64bit integer math (32bx32b, 32b+32b).
>
> I could reinvent the wheel,
> but figure this has to be out there
> in multiple places for free.
>
> Any suggestions for free
> C source for 64bit integer math?

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

static void add64(uint32_t a, uint32_t b, uint32_t *prh, uint32_t *prl)
{
uint32_t rl = a + b;
uint32_t rh = rl < a;

*prl = rl;
*prh = rh;
}

/*
(k*ah + al) * (k*bh + bl)
= k*k*ah*bh + k*(ah*bl + al*bh) + al*bl
*/

static void mul64(uint32_t a, uint32_t b, uint32_t *prh, uint32_t *prl)
{
uint32_t ah = a >> 16, al = a & 0xFFFFU;
uint32_t bh = b >> 16, bl = b & 0xFFFFU;
uint32_t rl = al * bl;
uint32_t rm1 = ah * bl;
uint32_t rm2 = al * bh;
uint32_t rh = ah * bh;
uint32_t rm1h = rm1 >> 16, rm1l = rm1 & 0xFFFFU;
uint32_t rm2h = rm2 >> 16, rm2l = rm2 & 0xFFFFU;
uint32_t rml = rm1l + rm2l;
uint32_t rmh = rm1h + rm2h;

rl += rml << 16;
if (rml & 0xFFFF0000U)
rmh++;
rh += rmh;

*prl = rl;
*prh = rh;
}

int main(int argc, char **argv)
{
uint32_t a, b, rl, rh;
uint64_t r;

if (argc != 3)
return 1;

a = (uint32_t) strtoul(argv[1], NULL, 0);
b = (uint32_t) strtoul(argv[2], NULL, 0);

mul64(a, b, &rh, &rl);
r = ((uint64_t) rh << 32) + rl;
printf("%08x * %08x = %16llx\n", (unsigned) a, (unsigned) b, (unsigned long long) r);
printf("%08x * %08x = %16llx\n", (unsigned) a, (unsigned) b, (unsigned long long) a * b);

add64(a, b, &rh, &rl);
r = ((uint64_t) rh << 32) + rl;
printf("%08x + %08x = %16llx\n", (unsigned) a, (unsigned) b, (unsigned long long) r);
printf("%08x + %08x = %16llx\n", (unsigned) a, (unsigned) b, (unsigned long long) a + b);

return 0;
}


From: Jon Kirwan on 26 Sep 2009 15:59
On Sat, 26 Sep 2009 06:37:02 -0700, Andrew <asmith(a)blackstone.biz>
wrote:

>Jon Kirwan wrote:
>> On Wed, 23 Sep 2009 12:48:23 -0700, Andrew <asmith(a)blackstone.biz>
>> wrote:
>>
>>> I'm using CodeVision C compiler on an AVR.
>>> CodeVision has 32bit limitation for integers.
>>> I need to do 64bit integer math (32bx32b, 32b+32b).
>>>
>>> I could reinvent the wheel,
>>> but figure this has to be out there
>>> in multiple places for free.
>>>
>>> Any suggestions for free
>>> C source for 64bit integer math?
>>
>> Looks like you already posted this up on avrfreaks and got some
>> replies. I didn't really understand your 32b+32b request, as that
>> requires only 33 bits -- only one bit is valid in the upper 32-bit
>> word of a 64-bit result for unsigned, if that's what you wanted. It's
>> not hard to generate for unsigned, but slightly more trouble for
>> signed. Also, you didn't specify signed vs unsigned or whether you'd
>> like to mix the two types, which compounds the problem of providing
>> any useful answer. And you didn't address speed or code size. I
>> gather you want this entirely in c, though, and don't want anything
>> more than multiplication and addition operations?
>>
>> Tell us where you are now and fill in some more details, if you don't
>> already have a solution from posting elsewhere. Might be a better
>> shot at an answer here, then.
>>
>> Jon
>>
>> P.S. If you are looking for generalized code in c, there is a book I
>> might point you towards which gets right down into the details of a
>> fairly general purpose, expandable set of routines entirely in c.
>
>All I really needed was to add unsigned 32bit int to a unsigned 64bit
>int with restrictions that 32bit is largest int that can be defined.

I'm really not following this. I'm sorry, as it might just be my
fault in the way I am interpreting what you write. If a 32 bit result
is the largest result allowed (and I'm assuming that is what you mean
regarding the restriction) adding a 32 bit unsigned to a 64 bit
unsigned is even easier than you mention below. There is no need to
compute a 33rd bit. So I have to assume I don't understand your
restriction. I'm not even sure how you pass in the 64 bit int, nor
what size the function _result_ fits, to be honest. And you earlier
wrote "32b+32b" which seems to differ from today, too. So there is a
lot I still don't feel confident about understanding. Too much to be
of much use, I figure.

>Not hard, however, it was suggested that I get a general integer lib
>that could do everything; signed/unsigned, mul/div/sub/add.
>
>I didn't find anything initially that included what I needed
>so wrote the add. Have to break it down into 16bit segments
>to get the carry right for 33d bit. Would still like to find
>a free lib. May need the other functions in the future.
>Got to be several free libs out there.

There are. But well-healed ones are pretty big and do a lot more than
you are initially asking. You still haven't described speed, code
size, or how often these functions are required relative to the
overall application. So I can't even offer some thoughts.

Well, best of luck. Maybe someone else understands exactly what you
need and where to find it.

Jon
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