I barely need to say that I'm not an expert, but by a closer
inspection I realized that most of the code is equivalent except that
there is a notorious difference in the way the ampp array is indexed:

5.08
   do {
      if (denom > FL(0.0002) || denom < -FL(0.0002)) {
        *ar++ = last = num / denom * scal;
      }
      else if (last<0)
        *ar++ = last = - *ampp;
      else
        *ar++ = last = *ampp;
      if (p->ampcod)
        scal =  p->rsumr * *(++ampp);
      ....
    } while (--nn);


5.09:
 for (n=0;;) {
   ...
  if (denom > FL(0.0002) || denom < -FL(0.0002)) {
        ar[n] = last = num / denom * scal;
      }
      else if (last<0)
        ar[n] = last = - ampp[n];
      else
        ar[n] = last = ampp[n];
      ....
      if (++n>=nn) break;
      if (p->ampcod)
        scal =  p->rsumr * ampp[n];
      ....
    }

Notice that in 5.08 ampp is advanced only if p->ampcod (I assume the
condition means that in this case ampp is a-rate instead of i/k-rate).
But in 5.09 n is incremented after each iteration, so ampp[n] will
reference positions beyond 0 even if ampp is i/k-rate.

I think this is causing the problem I experienced because replacing
ampp[n] for ampp[0] gbuzz works fine for i-rate amps.

One fix can be going back to 5.08 for the ampp stuff:

52c52
<         ar[n] = last = - ampp[n];
---
>         ar[n] = last = - *ampp;
54c54
<         ar[n] = last = ampp[n];
---
>         ar[n] = last = *ampp;
58c58
<         scal =  p->rsumr * ampp[n];
---
>         scal =  p->rsumr * *(++ampp)

You have the last word.

Regards
-Carlos

On Wed, Nov 5, 2008 at 12:07 PM, Carlos Pita <carlosjosepita@gmail.com> wrote:
> Hi,
>
> I've been having problems with gbuzz with kmul ~ 1. You can see the
> details in my recent 'gbuzz with kmul = 1' posts to the users' list. I
> noticed that the ill behavior only occurs in version 5.09 (both for
> float and double samples). A diff for gbuzz function in ugens4.c
> comparing .08 against .09 shows a number of recent changes. So I
> replaced the .09 implementation with the old one and recompiled. That
> fixed the issue. I've no time now to further isolate the specific
> cause, I'll continue later. Following is the aforementioned diff.
>
> Regards
> -Carlos
>
> <     long        phs, inc, lobits, lenmask, k, km1, kpn, kpnm1, nn;
> <     long        n;
> ---
>>     int32       phs, inc, lobits, lenmask, k, km1, kpn, kpnm1, nn;
>>     int32       n;
> 9c9
> <     long        lphs = p->lphs;
> ---
>>     int32       lphs = p->lphs;
> 12,14c12
> <     if (ftp==NULL) {
> <       return csound->PerfError(csound, Str("gbuzz: not initialised"));
> <     }
> ---
>>     if (ftp==NULL) goto err1;
> 20,21c18,19
> <     k = (long)*p->kk;                   /* fix k and n  */
> <     if ((n = (long)*p->kn)<0) n = -n;
> ---
>>     k = (int32)*p->kk;                   /* fix k and n  */
>>     if ((n = (int32)*p->kn)<0) n = -n;
> 29c27
> <       p->twor = r * FL(2.0);
> ---
>>       p->twor = r + r;
> 31c29
> <       p->rtn = intpow(r, n);
> ---
>>       p->rtn = intpowp(r, n);
> 37c35
> <       p->prvn = (short)n;
> ---
>>       p->prvn = (int16)n;
> 40c38
> <     inc = (long)(*cpsp * csound->sicvt);
> ---
>>     inc = (int32)(*cpsp * csound->sicvt);
> 43c41
> <     do {
> ---
>>     for (n=0;;) {
> 45,49c43,47
> <       denom = p->rsqp1 - p->twor * *(ftbl + phs);
> <       num = *(ftbl + (phs * k & lenmask))
> <         - r * *(ftbl + (phs * km1 & lenmask))
> <         - p->rtn * *(ftbl + (phs * kpn & lenmask))
> <         + p->rtnp1 * *(ftbl + (phs * kpnm1 & lenmask));
> ---
>>       denom = p->rsqp1 - p->twor * ftbl[phs];
>>       num = ftbl[(phs * k & lenmask)]
>>         - r * ftbl[(phs * km1 & lenmask)]
>>         - p->rtn * ftbl[(phs * kpn & lenmask)]
>>         + p->rtnp1 * ftbl[(phs * kpnm1 & lenmask)];
> 51c49
> <         *ar++ = last = num / denom * scal;
> ---
>>         ar[n] = last = num / denom * scal;
> 54c52
> <         *ar++ = last = - *ampp;
> ---
>>         ar[n] = last = - ampp[n];
> 56c54,56
> <         *ar++ = last = *ampp;
> ---
>>         ar[n] = last = ampp[n];
>>       lphs = (lphs+inc) & PHMASK;
>>       if (++n>=nn) break;
> 58,60c58
> <         scal =  p->rsumr * *(++ampp);
> <       lphs += inc;
> <       lphs &= PHMASK;
> ---
>>         scal =  p->rsumr * ampp[n];
> 62,63c60,61
> <         inc = (long)(*(++cpsp) * csound->sicvt);
> <     } while (--nn);
> ---
>>         inc = (int32)(cpsp[n] * csound->sicvt);
>>     }
> 66a65,66
>>  err1:
>>     return csound->PerfError(csound, Str("gbuzz: not initialised"));
>

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