HI All,

Regarding Dave Akbari's new opcodes (very much enjoying logcurve,
btw!), I have just gotten around to working with them and had a couple
suggestions for changes:

1)the gainslider opcode documentation mentions:

"There is no bounds in the source code so you can for example give
higher than 127 values for extra amplitude but possibly clipped
audio."

but the code given does seem to have bounds and also a possible bug situation:

int gainslider_init(CSOUND *csound, gainslider *p)
{
    *p->koutsig = GAINSLIDER((MYFLT) *p->kindex);

    return OK;
}

int gainslider_perf(CSOUND *csound, gainslider *p)
{

    if (*p->kindex >= FL(0.0) && *p->kindex <= FL(152.0)) {
      *p->koutsig = GAINSLIDER((MYFLT) *p->kindex);
  }

  return OK;
}

For the init method, it does an initialization of the value against a
kindex, but kindex may not be initialized at i-time.  If this happens,
and kindex later at k-time is a value below 0 or above 152, the
koutsig is always going to return the value from the init.  Now, this
is a question I don't know the answer to: is a k-rate variable
initialized to 0 when the pointer is allocated or is it just
allocated?  I'd like to propose the init function be removed and the
performance function be changed to:

int gainslider_perf(CSOUND *csound, gainslider *p)
{

    if(*p->kindex <= FL(0.0)) {
        *p->koutsig = FL(0.0);
    } else {
        *p->koutsig = GAINSLIDER((MYFLT) *p->kindex);
   }

   return OK;
}

This will also alleviate if ksmps is high and ksig happens to jump
from a valid value to an invalid value (in the old code) that the last
value from gainslider isn't being returned.

2)the logcurve, expcurve, and scale init functions also don't seem
necessary as they're operating on a kval which may not be initialized.
 These could probably removed as they're not doing any initial
precalculations of state data or anything like that, and the thread
for the OENTRY can be changed to 2.

3)The documentation to logcurve mentions ksteepness should not be <=
1, but doesn't mention much in regards to how that value affects the
generated curve.  I had to look at the formula and run some data
through using different steepness values to figure out that values
closer to 1 make it steeper while higher values flatten out the curve
(is that right?).  If so, I think adding a little more text to
describe that parameter will make it a little more intuitive to those
first coming across the opcode (which, btw, has become my favorite
opcode of the day! Thanks Dave!).  Also, should we add the formula for
this opcode into the documentation?  I imagine some users who are
mathematically savvy but aren't interested to dig into the code might
want to know what the formula is to plot out curves for themselves to
find what they're looking for.

4)Same general comments as 3 but for expcurve (with the info flipped
for suggested values for steepness)

5)expcurve code seems to be wrong to me!  This is the macro defined in ugakbari:

#define EXPCURVE(x,y) (exp(x * log(y))-1/(y-1))

while the UDO code is:

kout	=	(exp(kfloat * log(ksteep)) - 1)/(ksteep - 1)

I only noticed just now when trying to plot some values and I used the
values from the macro.  It seems it is missing some parentheses and
should be:

#define EXPCURVE(x,y) ((exp(x * log(y))-1)/(y-1))


Just wanted to note that I hope these comments are taken purely as
constructive and that I'm very happy these opcodes are in! (Thanks
Dave!)

steven

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