tablera, tablewa

   ar       tablera     kfn, kstart, koff
   kstart   tablewa     kfn, asig, koff

DESCRIPTION

INITIALIZATION

kfn - i or k rate number of the table to read or write.

kstart - Where in table to read or write.

asig - a rate signal to read from when writing to the table.

koff - i or k rate offset into table. Range unlimited - see explanation at end of this section.

PERFORMANCE

These read from and write to sequential locations in a table at audio rates, with ksmps floats being written and read each cycle.

tablera starts reading from location kstart. tablewa starts writing to location kstart, and then writes to kstart with the number of the location one more than the one it last wrote. (Note that for tablewa, kstart is both an input and output variable.) If the writing index reaches the end of the table, then no further writing occurs and zero is written to kstart.

For instance, if the table's length was 16 (locations 0 to 15), and ksmps was 5. Then the following steps would occur with repetitive runs of the tablewa ugen, assuming that kstart started at 0.

Run no. Initial  Final    locations written
        kstart   kstart

1       0        5        0 1 2 3 4
2       5        10       5 6 7 8 9
3       10       15       10 11 12 13 14
4       15       0        15

Notes on tablera and tablewa :

These are a fudge, but they allow all Csounds k rate operators to be used (with caution) on a rate variables - something that would only be possible otherwise by ksmps = 1, downsamp and upsamp.

Several cautions:

• The k rate code in the processing loop is really running at a rate, so time dependant functions like port and oscil work faster than normal - their code is expecting to be running at k rate.
• This system will produce undesirable results unless the ksmps fits within the table length. For instance a table of length 16 will accomodate 1 to 16 samples, so this example will work with ksmps = 1 to 16.

Both these ugens generate an error and deactivate the instrument if a table with length < ksmps is selected. Likewise an error occurs if kstart is below 0 or greater than the highest entry in the table - if kstart >= table length.

• kstart is intended to contain integer values between 0 and (table length - 1). Fractional values above this should not affect operation but do not achieve anything useful.
• These ugens do not do interpolation and the kstart and koff parameters always have a range of 0 to (table length - 1) - not 0 to 1 as is available in other table read/write ugens. koff can be outside this range but it is wrapped around by the final AND operation.
• These ugens are permanently in wrap mode. When koff is 0, no wrapping needs to occur, since the kstart++ index will always be within the table's normal range. koff != 0 can lead to wrapping.
• The offset does not affect the number of read/write cycles performed, or the value written to kstart by tablewa.
• These ugens cannot read or write the guardpoint. Use tablegpw to write the guardpoint after manipulations have been done with tablewa.

EXAMPLES:

                                  
 kstart   =       0      ; Read 5 values from table into an 
                         ; a rate variable.
 lab1:
   atemp  tablera ktabsource, kstart, 0 
                         ; Process the values using a rate code.
   atemp  =       log(atemp)    ; Write it back to the table
   kstart tablewa ktabdest, atemp, 0 
         ; Loop until all table locations have been processed.
 if ktemp > 0 goto lab1

This enables whole tables, parts of tables (with offsets and different control loops) and data from several tables at once to be manipulated with a rate code and written back to another (or to the same) table. This is a bit of a fudge, but it is faster than doing it with k rate table read and write code.

Another application is:

   kzero = 0                    
   kloop = 0                    
                                 
   kzero tablewa 23, asignal, 0 ; ksmps a rate samples written
                                ; into locations 0 to (ksmps -1) of table 23.
                                
   lab1: ktemp table kloop, 23  ; Start a loop which runs ksmps times, 
                                ; in which each cycle processes one of 
    [ Some code to manipulate ] ; table 23's values with k rate orchestra
    [ the value of ktemp. ]     ; code.
                                 
    tablew ktemp, kloop, 23     ; Write the processed value to the table.
                                ;
   kloop = kloop + 1            ; Increment the kloop, which is both the
                                ; pointer into the table and the loop 
   if kloop < ksmps goto lab1   ; counter. Keep looping until all values
                                ; in the table have been processed.
                                
   asignal   tablera 23, 0, 0   ; Copy the table contents back
                                ; to an a rate variable.

Ideally this would be an optional variable, defaulting to 0, however with the existing Csount orchestra read code, such default parameters must be init time only. We want k rate here, so we cannot have a default.