--- In DynoMotion@yahoogroups.com, Tom Kerekes <tk@...> wrote:
>
> Hi Ray,
>  
> s[-1]  : since s is a pointer into the middle of a char array then s[-1] is the char one slot before where s points.
>  
> The first parameter (PERSIST+1) is not a pointer.  It is an offset into the gather_buffer for where the string is located.  It is passed at the very beginning so the offset is set to zero.  The gather_buffer is sort of a general purpose global block of 8MBytes of SDRAM.
>  
> TK
>
> From: himykabibble <jagboy@...>
> To: DynoMotion@yahoogroups.com
> Sent: Sunday, January 29, 2012 8:35 AM
> Subject: [DynoMotion] Coupla Stupid Questions....
>
>
>  
> I'm working on the PCComm methods, and am finding some seemingly simple things that I'm, just not grok'ing.
>
> 1) In the DSP code for PC_COMM_MSG, I find the following code:
>
> int MsgBox(char *s, int Flags)
> {
> char *p=(char *)gather_buffer+GATH_OFF*sizeof(int);
> int i;
>
> do // copy to gather buffer w offset 0
> {
> *p++ = *s++;
> }while (s[-1]);
>
> persist.UserData[PC_COMM_PERSIST+2] = Flags; // set options
> DoPCInt(PC_COMM_MSG,GATH_OFF);
> return persist.UserData[PC_COMM_PERSIST+3];
> }
>
> Two things confuse me here:
>
> First, is the "while (s[-1]);". That's obviously being used to detect the end of the string, but how? What is at s[-1]??
>
> Second, as I understand this method, PC_COMM_PERSIST is set to PC_COMM_MSG and PC_COMM_PERSIST+1 should be set as a pointer to the string. But PC_COMM_PERSIST+1 doesn't get set at all here?? And, indeed, when I try to use PC_COMM_PERSIST+1 as the string offset, I get garbage.
>
> Regards,
> Ray L.
>

--- In DynoMotion@yahoogroups.com, "himykabibble" <jagboy@...> wrote:
>
> Tom,
>
> Ah! That's what I was missing.... Thanks. It's working now.
>
> Regards,
> Ray L.
>
> --- In DynoMotion@yahoogroups.com, Tom Kerekes <tk@> wrote:
> >
> > Hi Ray,
> >  
> > s[-1]  : since s is a pointer into the middle of a char array then s[-1] is the char one slot before where s points.
> >  
> > The first parameter (PERSIST+1) is not a pointer.  It is an offset into the gather_buffer for where the string is located.  It is passed at the very beginning so the offset is set to zero.  The gather_buffer is sort of a general purpose global block of 8MBytes of SDRAM.
> >  
> > TK
> >
> > From: himykabibble <jagboy@>
> > To: DynoMotion@yahoogroups.com
> > Sent: Sunday, January 29, 2012 8:35 AM
> > Subject: [DynoMotion] Coupla Stupid Questions....
> >
> >
> >  
> > I'm working on the PCComm methods, and am finding some seemingly simple things that I'm, just not grok'ing.
> >
> > 1) In the DSP code for PC_COMM_MSG, I find the following code:
> >
> > int MsgBox(char *s, int Flags)
> > {
> > char *p=(char *)gather_buffer+GATH_OFF*sizeof(int);
> > int i;
> >
> > do // copy to gather buffer w offset 0
> > {
> > *p++ = *s++;
> > }while (s[-1]);
> >
> > persist.UserData[PC_COMM_PERSIST+2] = Flags; // set options
> > DoPCInt(PC_COMM_MSG,GATH_OFF);
> > return persist.UserData[PC_COMM_PERSIST+3];
> > }
> >
> > Two things confuse me here:
> >
> > First, is the "while (s[-1]);". That's obviously being used to detect the end of the string, but how? What is at s[-1]??
> >
> > Second, as I understand this method, PC_COMM_PERSIST is set to PC_COMM_MSG and PC_COMM_PERSIST+1 should be set as a pointer to the string. But PC_COMM_PERSIST+1 doesn't get set at all here?? And, indeed, when I try to use PC_COMM_PERSIST+1 as the string offset, I get garbage.
> >
> > Regards,
> > Ray L.
> >
>