The Spade Hardware Description Language

if-expressions

Syntax

if expression block else block

The if-expression looks a lot like an if-statement in languages you may be used to, but unlike most languages where if is used to conditionally do something, in Spade, it is used to select values.

For example, the following function returns a if select_a is true, otherwise it returns b.

Functions together with Entities together with fn and Defines a pipeline. The number in in the parentheses is input-to-output latency of the pipeline. are the basic building blocks of Spade circuits. Unlike fn, entity can contain registers and therefore have state and unlike Defines a pipeline. The number in in the parentheses is input-to-output latency of the pipeline., they do not have a statically known latency or Defines a pipeline. The number in in the parentheses is input-to-output latency of the pipeline. structure. and Defines a pipeline. The number in in the parentheses is input-to-output latency of the pipeline. are the basic building blocks of Spade circuits. Unlike entities and pipelines, functions have no internal state, they are combinational (pure). select(select_a: Type used to represent 1 bit values, a: Type used to represent signed integers. The generic parameter (<N>) specReturns the value of the first branch if the condition is true, otherwise the second branch.
Note that unlike software languages, Spade does not have conditional execution. You do not conditionally assign values inside if expressiosn, you compute a value and return it.ies the number of bits, b: Type used to represent signed integers. The generic parameter (<N>) specReturns the value of the first branch if the condition is true, otherwise the second branch.
Note that unlike software languages, Spade does not have conditional execution. You do not conditionally assign values inside if expressiosn, you compute a value and return it.ies the number of bits) -> Type used to represent signed integers. The generic parameter (<N>) specReturns the value of the first branch if the condition is true, otherwise the second branch.
Note that unlike software languages, Spade does not have conditional execution. You do not conditionally assign values inside if expressiosn, you compute a value and return it.ies the number of bits {
    Returns the value of the first branch if the condition is true, otherwise the second branch.
Note that unlike software languages, Spade does not have conditional execution. You do not conditionally assign values inside if expressiosn, you compute a value and return it. select_a {
        a
    } else {
        b
    }
}

This code makes heavy use of blocks. The body of the function, as well as each if-branch is a block.

In traditional hardware description languages, this would instead look like

fn select(select_a: bool, a: int<8>, b: int<8>) -> int<8> {
    var result;
    if select_a {
        result = a;
    } else {
        result = b;
    }
    return result
}

but the Spade version is much closer to the actual hardware that is generated. Hardware in general does not support conditional execution, it will evaluate both branches and select the result.