Memory Array Pointer to Long

sobakava

I've tables located in the memory and it is defined like this:

my_table1 byte $10 , $15
byte $12 , $20
.
.

my_table2 byte $17 , $11
byte $13 , $22
.
.

I am accesing this data in this way:

blabla :=  my_table1[ 4 ] * my_table1[ 5 ]

but I want to use another table instead of the first one. I thought I can use a pointer (long) and use it like this:

long my_table_pointer
.
.
.
.
if ( table_nr == 1 )
my_table_pointer := my_table1
if ( table_nr == 2 )
my_table_pointer := my_table2
.
.
[code]blabla := my_table_pointer[ 4 ] * my_table_pointer[ 5 ]

But it seems this approach does not work. I read incorrect data from memory.

What is the most convenient way to do this? I don't want to replicate blabla calculations using if conditions for each table because it requires a lot of memory space.

Thanks!

tonyp12

>blabla := my_table_pointer[ 4 ] * my_table_pointer[ 5 ]

Will not work.
Are all the tables the same lenght, say 32 bytes?
If so put them after each other.

blabla := my_table1[ 4 + table_nr *32] * my_table1[ 5 + table_nr *32]

JonnyMac

You can use a pointer if you assign it before the table access -- something like this

table1pntr := @table1
  table2pntr := @table2
  result := byte[table1pntr][index1] * byte[table2pntr][index2]

Note that when fetching values this way you need to be explicit as to the size of the elements in your table, hence byte[][] was used.

Dave Hein

You could use an array of pointers as follows:

my_table1 byte $10 , $15
byte $12 , $20
.
.
my_table2 byte $17 , $11
byte $13 , $22
.
.
my_table word @my_table1, @my_table2
.
.
blabla := byte[@@my_table[idx1]][4] * byte[@@my_table[idx2]][5]

idx1 and idx2 would have values of 0 or 1. The addresses stored in my_table are object offsets, so you need to use the @@ operator to get the absolute address. The object offsets could be converted to absolute address at the beginning of the program so you would not have to use the @@ operator later on. That would look something like this:

repeat i from 0 to 1
  my_table[i] := @@my_table[i]
.
.
blabla := byte[my_table[idx1]][4] * byte[my_table[idx2]][5]

Dave Hein

My previous example may be more complex than you need if idx1 equals idx2, which equals nr. In that case you could use my_table_ptr as follows:

my_table_ptr := @@my_table[nr-1]
blabla := byte[my_table_ptr][4] * byte[my_table_ptr][5]