olo_base_pkg_math.md

olo_base_pkg_math

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VHDL Source: olo_base_pkg_math

Description

This package contains different mathematics functions not defined in IEEE packages but used by Open Logic internally or on its interfaces to the user (e.g. for port-widths depending on generics). The package is written mainly for these purposes and does not aim for completeness - nevertheless as a user you are free to use it for your code of course.

The package uses array-types (e.g. t_abool or t_areal) defined in olo_base_pkg_array.

Definitions

None

Functions

log2()

Calculate the binary logarithm of an integer number.

function log2(arg : in natural) return natural;

log2ceil()

Calculate the binary logarithm of an integer number and round the result up.

function log2ceil(arg : in natural) return natural;

This function can be used to calculate the number of bits required to represent a given number. An example for this usage is given below.

signal UpToThousand : std_logic_vector(log2ceil(1000)-1 downto 0);

Note that log2ceil() implements a special case for zero as input. Although the mathematically correct result would be minus infinity the function returns zero. This special case handling is useful for the usecase depicted above - returning zero results in a valid zero-length array instead of a compile error.

isPower2()

Check if a number is a a power of two.

function isPower2(arg : in natural) return boolean;

max() / min()

Return the smaller or larger value out of two.

function max(a : in <T>; b : in <T>) return <T>;
function min(a : in <T>; b : in <T>) return <T>; 

Implemented for <T>: integer, real

choose()

Return one or the other value based depending on a boolean input. This is useful for decisions in constant calculations.

function choose(s : in boolean; t : in <T>; f : in <T>) return <T>;

Implemented for <T>: integer, real, std_logic, std_logic_vector, string, unsigned, boolean, t_areal

count()

Count the occurrences of a a given value in an array.

function count(a : in <A>; v : in <T>) return integer;

Implemented for the following <A> / <T> combinations:

• t_ainteger / integer
• t_abool / boolean
• std_logic_vector / std_logic

toUslv() / toSslv() / toStdl()

Convert an integer value to a signed/unsigned std_logic_vector representation of a given length or a std_logic representation.

function toUslv(input : integer; len   : integer) return std_logic_vector;
function toSslv(input : integer; len   : integer) return std_logic_vector;
function toStdl(input : integer range 0 to 1) return std_logic;

This function is implemented as pure simplification to avoid typing the very popular conversion below over and over again:

a := std_logic_vector(to_unsigned(someInteger, a'length));
-- The same can now be written simpler
a := toUslv(someInteger, a'length);

fromUslv() / fromSslv() / fromStdl()

Convert a signed/unsigned std_logic_vector value or a std_logic value into integer representation.

function fromUslv(input : std_logic_vector) return integer;
function fromSslv(input : std_logic_vector) return integer;
function fromStdl(input : std_logic) return integer;

This function is implemented as pure simplification to avoid typing the very popular conversion below over and over again:

a := to_integer(unsigned(someStdLogicVector));
-- The same can now be written simpler
a := fromUslv(someStdLogicVector);

fromString()

This function converts a string into other types.

function fromString(input : string) return <T>;

The <T> types is is implemented for plus some examples of the strings it takes for the corresponding conversion are given below:

• real
  • "1.234"
  • "-1.234e3"
  • "+5.67E-12"
• t_areal (real array)
  • "1.234, -1.234e3, +5.67E-12"
  • Values separated by comma (,) and NO brackets

minArray() / maxArray()

Return the minumum / maximum value out of an array.

function maxArray(a : in <A>) return <T>;
function minArray(a : in <A>) return <T>;

Implemented for the following <A> / <T> combinations:

• t_ainteger / integer
• t_areal / real