System Verilog - data type

One 、 Built in data type

Four valued logic type	Binary logic type
logic integer reg net-type	byte int longint shortint bit

There are sign types	Unsigned type
byte integer int longint shortint	logic bit reg net-type

Tips:
（1） The default value returned by the four value status is x, The default value returned by binary status is 0.
（2）logic Type can only have one driver .
（3） The output of the network is when there is no driver z.

Two 、 Array

1. Fixed width array

Declaration of fixed width array

int array_lo_hi[0:15];//16 It's an integer [0]...[15]
int array_c_style[16];//16 It's an integer [0]...[15]

Declaration of multidimensional array

int array1 [0:7][0:3];// Complete statement 
int array2 [8][4];// A compact statement 
array1[7][3] = 1;// Set the last element 

Initialization of constant array

int ascend[4] = '{
    0, 1, 2, 3};// Initialize the four elements 
int descend[5];

descend = '{
    4, 3, 2, 1, 0};// Assign values to five elements 
descend[0:2] = '{
    5, 6,  7};// Assign values to the first three elements 
ascend = '{
    4{
    8}};// Assign all four values to 8
ascend = '{
    9, 8, default:1};// The assignment is {9,8,1,1,1}

Basic array operations
<1> foreach
Syntax format of multidimensional array traversal

int md[2][3] = '{
     '{
    0, 1, 2}, '{
    3, 4, 5}};
foreach(md[i, j])
	$display("md[%0d][%0d]=%0d", i, j, md[i, j]);

For arrays f[0:4] Come on ,foreach(f[i]) Equate to

for(int i=0;i<=4;i++)

For arrays rev[6:2] Come on ,foreach(rev[i]) Equate to

for(int i=6;i>=2; i--)

<2> Copy and compare

dst == src;// hold src All elements of the are copied to dst

Use “？：” Operators for comparison ,
Such as A?B:C, Judge A,A Carry out for real B, Otherwise execution C.

<3> Use of merged and non merged arrays

Merge / Declaration of unconsolidated mixed arrays

bit[3:0][7:0]barray[3];// A non merged array with three merged elements ,3x32 The bit 
bit[31:0]lw = 32'h0123_4567;// One word 
bit[7:0][3:0]nibbles;// Merge array 

barray[0] = lw;// Use a subscript , You can get one word of data 
barray[0][3] = 8'h01;// Use two subscripts , You can get a byte of data 
barray[0][1][6] = 1'b1;// Use three subscripts , A single bit can be accessed 
nibbles = barray[0];// Copy the element values of the merged array 

Tips：
（1） When declaring a merged array , The combined bit and array size must be specified before the variable name as part of the data type . The format of the array size definition must be [msb:lsb], instead of [size].
（2） The array declaration specifies the size of the array after the variable name barray[3], This dimension is not merged , So when using this array, there must be at least one subscript .

2. The dynamic array

（1） The width of a dynamic array is not given at compile time like a fixed width array , Instead, specify when the program is running .
（2） The array is empty at the beginning , Need to call new[ ] To allocate space , At the same time, pass the array width in square brackets .
（3） As long as the basic data types are the same , For example, it's all int, Fixed width array and dynamic array can be assigned to each other , With the same number of elements , You can copy the values of a dynamic array to a fixed width array .

int d1[],d2[];// Declare dynamic arrays 

initial begin
	d1 = new[5];// Assigned to d1 The five elements 
	foreach(d1[i])	d1[i] = i;// Initialize the element 
	d2 = d1;// Copy a dynamic array 
	d2[0] = 5;// Modify the copy value 
	$display(d1[0], d2[0]);// Display value （0 and 5）
	d1 = new[20](d1);// Distribute 20 An integer value and the original d1 The array is copied to the first five elements 
	d1 = new[100];// Distribute 100 A new integer value , The old value no longer exists 
	d1.delete();// Delete all elements 
end

3. Associative array

Associative arrays can be used to hold elements of sparse matrices , When you address a very large address space , The array only allocates space for the elements actually written , So that the occupied space is very small .

initial begin
	bit[63:0]assoc[bit[63:0]], idx = 1;
	// Initialize sparsely distributed elements 
	repeat(64) begin
		assoc[idx] = idx;
		idx = idx<<1;
	end
	// Use foreach Traversal array 
	foreach(assoc[i])
		$display("assoc[%h] = %h", i, assoc[i]);
end
	

4. Array method

1. Array reduction method （ Reduce an array to one value ）
   sum, Sum all the elements in the array .
   Besides , also product（ product ）,and（ And ）,or（ or ）,xor（ Exclusive or ）.
2. Array positioning method

// Array positioning method min, max, unique
int f[6] = '{
    1, 6, 2, 6, 8, 6};
int d[ ] = '{
    2, 4, 6, 8, 10};
int q[$] = '{
    1, 3, 5, 7}, tq[$];

tq = q.min();//{1}
tq = d.max();//{10}
tq = f.unique();//{1, 6, 2, 8}

// Array positioning method find
int d[ ] = '{
    9, 1, 8, 3, 4, 4}, tq[$];
// Find all that are greater than 3 The elements of 
tq = d.find with(item >3);//{9, 8, 4, 4}
// Equivalent code 
foreach (d[i])
	if (d[i])
		tq.push_back(d[i]);

tq = d.find_index with(item >3);//{0, 2, 4, 5},( namely 9, 8, 4, 4 Of index)
tq = d.find_first with(item >99);//{ } Can't find 
tq = d.find_first_index with(item == 8);//{2} d[2] = 8


// Array positioning method count and total
int count, total, d[ ] = '{
    9, 1, 8, 3, 4, 4};
count = d.sum with(item > 7);//2 {9, 8}
total = d.sum with((item > 7) * item);//17 1*9+1*8
count = d.sum with(item < 8);//4 {1, 3, 4, 4}
total = d.sum with(item < 8 ? item :0);//12 1+3+4+4
count = d.sum with(item == 4);//2 {4, 4}

3. Sort of array

int d[ ] = '{
    9, 1, 8, 3, 4, 4};
d.reverse();// reverse  {4, 4, 3, 8, 1, 9}
d.sort();// positive sequence  {1, 3, 4, 4, 8, 9}
d.rsort();// The reverse  {9, 8, 4, 4, 3, 1}
d.shuffle();// Shuffle  {9, 4, 3, 8, 1, 4}

3、 ... and 、 queue

1. It combines the advantages of linked list and array , You can add or remove elements anywhere else , And access to any element through the index .
2. The queue is declared using subscripts [ $ ], The label of the queue element is from 0 To $.（ You can use word subscripts to concatenate ,[ $:2 ] representative [0:2], [1 : $] representative [1:2].）
3. Queue not required new[ ] To create space , Just use its method to add or remove elements , At first, the space was 0.
4. The queue can pass through push_back() and pop_front() To achieve FIFO.

int j = 1;
q2[$] = {
    3, 4};// Queue constants do not need to use "'"
q[$] = {
    0, 2, 5};//{0, 2, 5}
initial begin
	q.insert(1, j);//{0, 1, 2, 5}  stay 2 Insert before 1
	q.insert(3, q2);//{0, 1, 2, 3, 4, 5}  stay q Insert a queue in 
	q.delete(1);//{0, 2, 3, 4, 5 }  Delete first element 
	q.push_front(6);//{6, 0, 2, 3, 4, 5}  Insert... In front of the queue 
	j = q.pop_back();//{6, 0, 2, 3, 4} j = 5
	q.push_back(8);//{6, 0, 2, 3, 4, 8}  Insert... At the end of the queue 
	j = q.pop_front();//{0, 2, 3 ,4, 8} j = 6
	foreach(q[i])
		$display(q[i]);// Print the entire queue 
	q.delete();// Delete the entire queue 
end

Four 、 character string

String method
getc（N）： return N Bytes at position .
toupper： Returns a string with all uppercase characters .
tolower： Returns a string with all characters in lowercase .
{ }： Used to concatenate strings .
putc（M, C）： Put bytes C Write to string M position .
substr(start, end)： Extract from position start To end All characters between .

string s;
initial begin
	s = "IEEE ";
	$display(s.getc(0));//73('I')
	$display(s.tolower());//ieee
	s.putc(s.len()-1, "-");// Change the space to '-'
	s = {
    s, "P1800"};//“IEEE-P1800”
	$display(s.substr(2, 5));//EE-P
end