builtins.md

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Built-in functions

Alogic provides a set of built-in functions, this section is a comprehensive reference of their semantics.

General semantics and concepts

Names of Alogic built-in functions start with either the $ or @ characters.

Built-in functions starting with a $ are borrowed from the Verilog language, and intended to behave as close to the corresponding Verilog function as possible, any relevant differences from the Verilog semantics of these function are described below. Note however that the syntax of function calls is of the Alogic syntax, and in particular a pair of empty () is required when calling function which take no arguments.

Built-in functions whose name starts with an @ are provided by Alogic and their semantics are defined below.

All built-in function calls are combinatorial statements when used in statement position.

Some built-in functions are overloaded, i.e.: they are available with multiple signatures, or have a generic signature.

List of $ built-in functions

Built-in $clog2

Signature:

uint $clog2(arg);

Returns the number of address bits required for a memory of the depth given by the argument. The argument must be a constant expression.

Built-in $signed

Signature:

int(N) $signed(expr);

Cast argument to a signed integer. The result is the same width as the argument. The argument can have any packed type.

Built-in $unigned

Signature:

uint(N) $unsigned(expr);

Cast argument to an unsigned integer. The result is the same width as the argument. The argument can have any packed type.

List of @ built-in functions

Built-in @bits

Signatures:

uint @bits(type);
uint @bits(expr);

@bits can be invoked on either a packed type, or an expression of packed type, and returns the number of width in bits of the argument. @bits is always evaluated at compile time.

Built-in @zx

Signatures:

uint(N) @zx(N, expr);
 int(N) @zx(N, expr);

Zero extend the second argument to the width specified by the first argument. The first argument must be a constant expression. The second argument can be any packed type with a width no greater than N. The result is unsigned if the second argument is unsigned, and the result is signed if the second argument is signed.

@zx(N, a) is the same as @ex(1'b0, N, a)

Built-in @sx

Signatures:

uint(N) @sx(N, expr);
 int(N) @sx(N, expr);

Sign extend the second argument to the width specified by the first argument. The first argument must be a constant expression. The second argument can be any packed type with a width no greater than N. The result is unsigned if the second argument is unsigned, and the result is signed if the second argument is signed.

Sign extending an unsigned value is defied as extension by the MSB.

@sx can only be called on arguments for which @msb is defined.

@sx(N, a) is the same as @ex(@msb(a), N, a)

Built-in @msb

Signature:

bool @msb(expr);

Evaluates to the MSB of the expression. Can only be be called on expression to which a [ ] index can be applied.

Built-in @ex

Signatures:

uint(N) @ex(bit, N, expr);
 int(N) @ex(bit, N, expr);

Extend the third argument to the width specified by the second argument, inserting the bit value given as the first argument into the MSBs of the result. The second argument must be a constant expression. The third argument can be any packed type with a width no greater than N. The result is unsigned if the second argument is unsigned, and the result is signed if the second argument is signed.

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