Re: error using unsigned long long not working in 2.4.x

Re: error using unsigned long long not working in 2.4.x

[Matti Aarnio]

On Mon, Mar 17, 2003 at 09:44:16PM -0800, dave wrote:
> hi i am writing a kernel 2.4.x driver and need to do maths on 64 bit ints
> (unsigned long long)
> bcause you can not use the FPU
> but when i insmod i get the error unresolved symbol __udivdi3 i need!! 64
> bit ints
> 
> i have included the code
> thank you

The original reason for Linux kernel not being linked with  -lgcc
where that routine is defined, is that of wanting to catch careless
coding of 64-bit arithmetic in kernel.  It does cause massiveish
performance penalty in the system, if used unchecked in code
fast paths.

If you can do it with at most 31 bit divider, and can handle 
side-effectfull division, system has   do_div()   macro.

Use like:

	#include <asm/div64.h>


	long long n, vco;
	long divisor;
	long remainder;

	n = vco;
	divisor = some_expression;
	remainder = do_div(n, divisor);


You will, most likely, ignore the remainder.
BECAUSE there is side-effect of modifying the dividend (n), you must
use it like in this illustriation.

The  divisor  can not have value in excess of 2^31.

Also there are architectures which do not properly implement this
routine, and do merely  32/32 division, where 64/32 is really wanted.
(The i386 architecture does handle it.)

/Matti Aarnio

Re: error using unsigned long long not working in 2.4.x

[Randy.Dunlap]

On Mon, 17 Mar 2003 21:44:16 -0800 "dave" <davekern@ihug.co.nz> wrote:

| hi i am writing a kernel 2.4.x driver and need to do maths on 64 bit ints
| (unsigned long long)
| bcause you can not use the FPU
| but when i insmod i get the error unresolved symbol __udivdi3 i need!! 64
| bit ints

Other alternatives are search the lkml archive for a patch from
George Anzinger on 2003-mar-05,
subject: [PATCH] Functions to do easy scaled math.

or if all you need is 64-bit mul and div, and only during setup
(when speed isn't a huge factor), you could use the divrem64()
function in this sample /procfs module:
  http://www.xenotime.net/linux/procfs_ex/procdiv64.c

--
~Randy

error using unsigned long long not working in 2.4.x

[dave]

[-- Attachment #1: Type: text/plain, Size: 247 bytes --]

hi i am writing a kernel 2.4.x driver and need to do maths on 64 bit ints
(unsigned long long)
bcause you can not use the FPU
but when i insmod i get the error unresolved symbol __udivdi3 i need!! 64
bit ints

i have included the code

thank you


[-- Attachment #2: lnvrm_nv05Pramdac.c --]
[-- Type: application/octet-stream, Size: 2231 bytes --]

#include <lnvrm.h>
#include <lnvrm_exports.h>

unsigned long nv05_pramdacPllCalc(struct _lnvrm_objNv01Device  *hw , unsigned long long clock)
{
  unsigned long long refClock  = hw->refClock ;
  unsigned long long vcoMax = 350000000 ;
  unsigned long long vcoMin =         0 ;
  unsigned long long nMax   =       255 ;
  unsigned long long nMin   =         1 ;
  unsigned long long mMax   =        14 ;
  unsigned long long mMin   =         1 ;
  unsigned long long pMax   =         4 ;
  unsigned long long pMin   =         1 ;
  unsigned long long f        ;
  unsigned long long fDif     ;
  unsigned long long fDifBest = ~0x00 ;
  unsigned long long fBest    = 0 ;
  unsigned long long nBest    = nMin ;
  unsigned long long mBest    = mMax ;
  unsigned long long pBest    = pMax ;
  unsigned long long vco   ;
  unsigned long long n     ;
  unsigned long long m     ;
  unsigned long long p     ;
  
  if(clock > vcoMax) clock = vco ;
  
  for(p = pMin ; p <= pMax ; p++) 
    {
      vco = clock * (1 << p) ;
      for(m = mMin ; m <= mMax ; m++)
	{
	  n = vco / (refClock / m) ;
	  if((n >= nMin) & (n <= nMax))
	    {
	      f = refClock / m * n ;
	      if(vco > f)
		fDif = vco - f ;
	      else
		fDif = f   - vco ;
	      if(fDif < fDifBest) { fDifBest = fDif ; fBest = f ; nBest = n ; mBest = m ; pBest = p ; } 
	    }
	}
    }
  printk("nv05_pramdacPllCalc: M:N:P %2.2LX:%2.2LX:%2.2LX f = %Ld Hz out = %Ld Hz\n",
	 mBest,
	 nBest,
	 pBest,
	 clock,
	 fBest / (1 << pBest));

  return((pBest << 16) | (nBest << 8) | mBest) ;
}

void nv05_pramdacSetPllNv(struct _lnvrm_objNv01Device  *hw , unsigned long long clock)
{
  unsigned long value ;
  value = nv05_pramdacPllCalc(hw,clock) ;
  nvr_regw(NV04_PRAMDAC_NVPLL_COEFF , value) ;
}

void nv05_pramdacSetPllMem(struct _lnvrm_objNv01Device  *hw , unsigned long long clock)
{
  unsigned long value ;
  value = nv05_pramdacPllCalc(hw,clock) ;
  nvr_regw(NV04_PRAMDAC_MPLL_COEFF , value) ;
}

void nv05_pramdacSetPllPixel(struct _lnvrm_objNv01Device  *hw , unsigned long long clock)
{
  unsigned long value ;
  value = nv05_pramdacPllCalc(hw,clock) ;
  nvr_regw(NV04_PRAMDAC_VPLL_COEFF , value) ;
}