int lo_hi[0:15];
int c_style[16];
//Array structure: [int] [int] [int] [int]  ...  [int]

✅ Key Point: Can be declared low-to-high or using C-style syntax.

Calculating address width

parameter int MEM_SIZE = 256;
parameter int ADDR_WIDTH = $clog2(MEM_SIZE); //$clog2(256)=8
bit [15:0] mem[MEM_SIZE];
bit [ADDR_WIDTH-1:0] addr;

/*
mem
Index:    mem[0]        mem[1]        mem[2]         ...       mem[255]
Data:   [15:0]        [15:0]        [15:0]                    [15:0]
Bits:   b15 ... b0    b15 ... b0    b15 ... b0        ...     b15 ... b0
*/

✅ Key Point: $clog2(MEM_SIZE) gives number of bits needed to address MEM_SIZE elements.

Multi-dimensional arrays

int array2 [0:7][0:3]; //Verbose declaration
int array3 [8][4]; //Compact declaration
Row \ Col 0 1 2 3
0 array2[0][0] array2[0][1] array2[0][2] array2[0][3]
1 array2[1][0] array2[1][1] array2[1][2] array2[1][3]
... ... ... ... ...
7 array2[7][0] array2[7][1] array2[7][2] array2[7][3]
✅ Key Point: First index = row, second index = column.

Unpacked Array

The example shown above are unpacked array. The values are stores in the
lower portion of the word, whereas the upper bits are unused.
Unpacked array storage.png

Packed Array

bit [3:0] [7:0] barray [5]; //5 elements: packed 4-bytes
bit [31:0] lw = 32'h0123_4567;
bit [7:0] [3:0] nibbles;
barray[0] = lw;
barray[0][3] = 8'h01;
barray[0][1][6] = 1'b1;
nibbles = barray[2];

✅ Key Point:

Packed array bit.png