C51: a lot of values assignment

I have three groups-(v1,...v50), (w1,...w50) and (y1,...y50), each group has 50 constant values.
By if-else condition, it needs to choose one group to assign the constant values
to "a" variables(a1,a2,...a50).

Instead of one by one assignment, I want to know if there is any other better coding method
that is more efficient and with smaller code or data memory size usage.

Please provide some suggestions. Thanks a lot!

I have three groups-(v1,...v50), (w1,...w50) and (y1,...y50), each group has 50 constant values.
By if-else condition, it needs to choose one group to assign the constant values
to "a" variables(a1,a2,...a50).

Instead of one by one assignment, I want to know if there is any other better coding method
that is more efficient and with smaller code or data memory size usage.

Please provide some suggestions. Thanks a lot!

I assume I'm doing your homework, anyway...

      unsigned char xdata a [50];
const unsigned char code  v [50] = {1,1,1,1,1,1,1,1 /* and so on up to all 50 */ };
const unsigned char code  w [50] = {2,2,2,2,2,2,2,2 /* and so on up to all 50 */ };
const unsigned char code  y [50] = {3,3,3,3,3,3,3,3 /* and so on up to all 50 */ };

void init_a (unsigned variant)
{
    switch(variant)
    {
    case 0: memcpy(a,v,sizeof(a)); break;
    case 2: memcpy(a,v,sizeof(a)); break;
    case 3: memcpy(a,v,sizeof(a)); break;
    default: /* cry for help */    break;
    }
}

/* Or maybe this? */

const unsigned char code * a2;
void init_a2 (unsigned variant)
{
    switch(variant)
    {
    case 0: a2 = v; break;
    case 2: a2 = w; break;
    case 3: a2 = y; break;
    default: /* cry for help */    break;
    }
}

"needs to choose one group to assign the constant values"

Does it really need to assign all the individual values?

Can't you just have a pointer and set that to point to the appropriate set of constants?

Hi Jane,

Thanks for your reply.

By Keil C51 v4 compiler, it shows your method 2 has smaller code memory usage than method 1.

In your method 2, about the pointer *a2:
Is *a2 being an array that consists 50 elements and can be assigned the values from v, w and y?

The value assignment is one by one mapping ?
Like a2[0] <-> v[0], a2[1] <-> v[1], ..., a2[50] <-> v[50]...etc ?

Thanks!

"Is *a2 being an array that consists 50 elements"

No!

a2 is a pointer which points to the start of one of the constant arrays - so there is no copying of the data!

Of course, in 'C', arrays & pointers are very closely related; eg, the indexing operator [] can be applied to a pointer:

*a2 dereferences the pointer; ie it gives the pointed-to item - which is the 1st element of one of the constant arrays.

a2[0] is equivalent to *a2.

a2[1] gives the second element of one of the constant arrays.

etc, etc,...

This is 'C' textbook stuff - nothing specific to the 8051, Keil, C51, or embedded.

c-faq.com/.../index.html

How about maybe respond with some answer to:
"Another thing - should you really assign 50 values? Or have change one pointer to point to a struct/array containing the specific set of 50 values? Is it real variable variables or do you use them as constants, where it would be possible to have them stored in code memory?"

There are no reason to waste RAM if we are talking about constants.