Variables in QUA¶

The following page describes the three types of variables in QUA: Integers, fixed point numbers and booleans.

Definitions¶

Integers¶

Integers in QUA are 32 bit, so their range is \([-2^{31}, 2^{31}-1]\) which is roughly \(\pm 2e9\).

To create an integer variable we declare() as follows:

i = declare(int)  # creates a variable named "i" of type integer

Warning

If assigning a value outside the range, the variable will overflow. When a variable overflows, the value will "wrap around". For example:

big_number = declare(int)
assign(big_number, 2**31-1)
# big_number is now 2^31-1
assign(big_number, big_number+1)
# big_number is now -2^31

Fixed point numbers¶

Fixed point numbers in QUA are in 4.28 format. There are 4 integer bits, including a sign bit, and 28 fractional bits. Therefore, the range of the fixed point number is \([-8, 8)\) in steps of \(2^{-28} = ~3.7e-9\).

To create a fixed variable we declare() as follows:

i = declare(fixed)  # creates a variable named "i" of type fixed point

Note

If assigning a value larger than 8, the variable will overflow. When a variable overflows, the value will be the modulo 16 unsigned, i.e. \(((x + 8) % 16) - 8\). In other words, the value will be wrapped around the range. For example:

\(8.0 \rightarrow -8.0\)
\(9.0 \rightarrow -7.0\)
\(17.0 \rightarrow 1.0\)
\(100.0 \rightarrow 4.0\)

Booleans¶

To create a boolean variable we declare() as follows:

b = declare(bool)  # creates a variable named "b" of type fixed boolean

When assigning the truth value of the boolean, every non-zero value will be considered as true, and zero will be false. For example:

b = declare(bool)

## True:
assign(b, True)
assign(b, 4<8)
assign(b, 2)
assign(b, 0.1)

## False:
assign(b, False)
assign(b, 4>8)
assign(b, 0)
assign(b, 0.0)

Casting¶

QUA enables casting between different types of variables using the Cast library. There are three normal casting operations, two casting by multiplication operations and two "unsafe" casting operations.

We list a few things to note while casting from one type to another:

Casting from int to fixed only gives an expected result when the integer is in the range [-8,7]. Otherwise, the result fixed variable will overflow.
Casting to Boolean, will behave according to the examples above.
The unsafe casting operation unsafe_cast_fixed() treats the input, bitwise, as a fixed number. When applied to an integer, this is equivalent to a multiplication by \(2^{-28}\).
The unsafe casting operation unsafe_cast_int() treats the input, bitwise, as an integer. When applied to a fixed number, this is equivalent to a multiplication by \(2^{28}\).