Indexing vectors and arrays with

Question

I am seeing a code in SystemVerilog which has something like this   if address 2 pointer  2     do something    How should I understand the    when indexing this vector   I found that it is called bit slicing  but I can t find an explanation about it

User · Accepted Answer

Description and examples can be found in IEEE Std 1800-2017 § 11.5.1 "Vector bit-select and part-select addressing". First IEEE appearance is IEEE 1364-2001 (Verilog) § 4.2.1 "Vector bit-select and part-select addressing". Here is an direct example from the LRM:

logic [31: 0] a_vect;
logic [0 :31] b_vect;
logic [63: 0] dword;
integer sel;
a_vect[ 0 +: 8] // == a_vect[ 7 : 0]
a_vect[15 -: 8] // == a_vect[15 : 8]
b_vect[ 0 +: 8] // == b_vect[0 : 7]
b_vect[15 -: 8] // == b_vect[8 :15]
dword[8*sel +: 8] // variable part-select with fixed width

If sel is 0 then dword[8*(0) +: 8] == dword[7:0]
If sel is 7 then dword[8*(7) +: 8] == dword[63:56]

The value to the left always the starting index. The number to the right is the width and must be a positive constant. the + and - indicates to select the bits of a higher or lower index value then the starting index.

Assuming address is in little endian ([msb:lsb]) format, then if(address[2*pointer+:2]) is the equivalent of if({address[2*pointer+1],address[2*pointer]})

User · Answer

This is another way to specify the range of the bit-vector   x    N   The start position of the vector is given by x and you count up from x by N   There is also   x -  N  in this case the start position is x and you count down from x by N   N is a constant and x is an expression that can contain iterators   It has a couple of benefits -   It makes the code more readable  You can specify an iterator when referencing bit-slices without getting a  cannot have a non-constant value  error

[system-verilog] Indexing vectors and arrays with +:

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