Namespace math

This namespace is used to provide support functions for math operations.

template<pint Worig, Wnew> function sign_extend (int<Worig> x) : int<Wnew>;

This function takes an integer x of width Worig, and sign extends its most significant bit to return a result that has width Wnew. It assumes that Wnew is at least Worig.

template<pint Worig, Wnew> function zero_extend (int<Worig> x) : int<Wnew>;

This function takes an integer x of width Worig, and zero extends it to return a result that has width Wnew. It assumes that Wnew is at least Worig.

The standard math library has a fixed point data type.

export template <pint A, B> deftype fixpoint(int<A+B> x);

This datatype uses the standard Q(A,B) fixed point format, where A bits are used for the integer part and B bits are used for the fractional part. This datatype defines operators for addition, subtraction, multiplication, division, as well as comparison operators.

The following code fragment initializes the fixed point value x to 5.25. x.const(5.25) returns a parameterized integer corresponding to translating the real number 5.25 to the fixed point representation used by x. Note that x.const() returns a pint, so it is limited to 64 bits. x.set() is a macro that takes an integer of bitwidth (A+B) and sets x to the specified fixed point number.

math::fixpoint<8,3> x;
...
chp {
    x.set(x.const(5.25));
    ...
}

Other ways to initialize x to the fixed point number corresponding to the integer representation 0x0f (which corresponds to 1.875 for Q(8,3)) are:

...
chp {
   x.x := 0x0f;
   ...
   x.set(0x0f);
   ...
}

For debugging purposes, two macros are also provided for displaying the value of a fixed point number. The log() macro just displays the number using the log() statement, while the log_p() displays it without a new line.

chp { 
   ...
   x.log();
   ...
}

The math::fxp namespace contains simple definitions for fixed-point arithmetic functions. Functions take two parameters A and B, and integers use the standard Q-format where the representation Q(A,B) corresponds to A digits for the integer part and B digits for the fractional part. The representation uses 2's complement for negative numbers, so addition and subtraction are the same for signed and unsigned arithmetic.

template<pint A,B> function add (int<A+B> x, y) : int<A+B>;

This returns the sum of two Q(A,B) numbers x and y.

template<pint A,B> function sub (int<A+B> x, y) : int<A+B>;

This returns the difference of two Q(A,B) numbers x and y.

template<pint A,B> function multu (int<A+B> x, y) : int<A+B>;

This returns the unsigned product of two Q(A,B) numbers x and y.

template<pint A,B> function divu (int<A+B> x, y) : int<A+B>;

This returns the unsigned division result x/y of two Q(A,B) numbers x and y.

template<pint A,B> function mults (int<A+B> x, y) : int<A+B>;

This returns the signed product of two Q(A,B) numbers x and y.

template<pint A,B> function divs (int<A+B> x, y) : int<A+B>;

This returns the signed division result x/y of two Q(A,B) numbers x and y.

template<pint A,B> function uminus (int<A+B> x) : int<A+B>;

This returns the negated value of a signed Q(A,B) number x.

template<pint A,B> function positive (int<A+B> x) : bool;

This is true if the fixed point number is positive (greater than zero), and false otherwise.

template<pint A,B> function negative (int<A+B> x) : bool;

This is true if the fixed point number is negative, and false otherwise

template<pint A,B> function le(int<A+B> x, y) : bool;

This tests if the value in x is less than or equal to y.

function conv_to_fxp(pint A, B; preal v) : pint;

This can be used to convert a real constant value into its fixed point representation. Note that since pint values are 64-bit wide (max), this only works when A+B is at most 64.

These functions are used by the fixed point data type.