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//
// Copyright 2021 Ettus Research, A National Instruments Brand
//
// SPDX-License-Identifier: LGPL-3.0-or-later
//
// Package: PkgRandom
//
// Description:
//
// SystemVerilog has great randomization support, but some features require a
// more expensive license or aren't supported by all tools. This package
// tries to fill that gap by providing some useful randomization functions
// beyond what's supported by standard Verilog.
//
package PkgRandom;
import PkgMath::*;
//---------------------------------------------------------------------------
// Functions
//---------------------------------------------------------------------------
// Return a real value in the range [0,max), where max is 1.0 by default.
function automatic real frand(real max = 1.0);
bit [63:0] real_bits;
real num;
// Build a double-precision floating point value per IEEE-754 standard,
// which SystemVerilog follows.
// Positive, with exponent 0
real_bits[63:52] = 12'h3FF;
// Mantissa in the range [1.0, 2.0). The leading 1 in the mantissa is
// implied by the floating point format.
real_bits[31: 0] = $urandom();
real_bits[51:32] = $urandom();
// Compensate for the implied leading 1 in the mantissa by subtracting 1.
num = $bitstoreal(real_bits) - 1.0;
// Scale the result to return a value in the desired range.
return num * max;
endfunction : frand
// Return a real value in the range [a,b), [b,a), or [0,a) depending on
// whether a or b is larger and whether b is provided. This matches the
// behavior of $urandom_range().
//
// frand_range(1.0, 2.0) -> Random value in the range [1,2)
// frand_range(2.0, 1.0) -> Random value in the range [1,2)
// frand_range(1.0) -> Random value in the range [0,1)
//
function automatic real frand_range(real a = 1.0, real b = 0.0);
if (a > b) return b + frand(a - b);
if (b > a) return a + frand(b - a);
return a;
endfunction : frand_range
// Return a real value with a normal distribution, having the mean value mu
// and standard deviation sigma.
function automatic real frandn(real sigma = 1.0, real mu = 0.0);
// Use the Box-Muller transform to convert uniform random variables to a
// Gaussian one.
return sigma*$sqrt(-2.0*$ln(frand())) * $cos(TAU*frand()) + mu;
endfunction : frandn
//---------------------------------------------------------------------------
// Template Functions
//---------------------------------------------------------------------------
class Rand #(WIDTH = 64);
// These are static class functions. They can be called directly, as in:
//
// Rand#(N)::rand_bit()
//
// Or, you can declare an object reference, as in:
//
// Rand #(N) rand;
// rand.rand_bit();
typedef bit [WIDTH-1:0] unsigned_t;
typedef bit signed [WIDTH-1:0] signed_t;
// Returns a WIDTH-bit random bit packed array.
static function unsigned_t rand_bit();
unsigned_t result;
int num_rand32 = (WIDTH + 31) / 32;
for (int i = 0; i < num_rand32; i++) begin
result = {result, $urandom()};
end
return result;
endfunction : rand_bit
// Returns a WIDTH-bit random number in the UNSIGNED range [a,b], [b,a], or
// [0,a] depending on whether a or b is greater and if b is provided. This
// is equivalent to $urandom_range() but works with any length.
static function bit [WIDTH-1:0] rand_bit_range(
unsigned_t a = {WIDTH{1'b1}},
unsigned_t b = 0
);
unsigned_t num;
int num_bits;
if (a > b) begin
// Swap a and b
unsigned_t temp;
temp = a;
a = b;
b = temp;
end
num_bits = $clog2(b - a + unsigned_t'{1});
do begin
num = a + (rand_bit() & ((unsigned_t'{1} << num_bits) - 1));
end while (num > b);
return num;
endfunction : rand_bit_range
// Returns a random number in the given SIGNED range. Behavior is the same
// as rand_bit_range(), bunsigned_t treats the range values as SIGNED numbers.
static function signed_t rand_sbit_range(
signed_t a = {1'b0, {WIDTH{1'b1}}},
signed_t b = 0
);
if (a > b) return b + $signed(rand_bit_range(0, a-b));
if (b > a) return a + $signed(rand_bit_range(0, b-a));
return a;
endfunction : rand_sbit_range
// Rand#(WIDTH)::rand_logic() returns a WIDTH-bit random logic packed
// array. Each bit will be 0 or 1 with equal probability (not X or Z).
static function logic [WIDTH-1:0] rand_logic();
return rand_bit();
endfunction : rand_logic
endclass : Rand
endpackage : PkgRandom
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