Indexing - The Spade Hardware Description Language

Array Indexing

Arrays can be indexed using []. Indices can either be single runtime integers such as [2] or [i], or compile-time ranges, such as [10..15]. Arrays are written and indexed zero-based as in most software languages. The leftmost array element is at index 0.

Single Element Indexing

Non-range indices can be runtime (unsigned) integers like [i]. The size of the index is the smallest power of two that can represent the size of the array. However, if the array size is not an even power of two, indexing outside the range causes undefined behavior.

Range Indexing

The indices for range indexing can only be integers known at compile time, i.e. not runtime values. Ranges take the form [i..j] where $𝑖 \leq 𝑗$ .

The beginning i of the range is included, and the end j of the range is excluded. For example, a[0..1] creates an array with a single element containing the first element of a.

Range indexing supports half-open ranges like [i..] and [..j] which extend all the way to the start or end of the array respectively.

Even the fully open range [..] is supported and selects the whole array.

Examples

// index:    0   1   2   3   4
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. array = [10, 11, 12, 13, 14];

letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[0]; // 10
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[1]; // 11
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[2]; // 12
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[5]; // Out of bounds access (array length is 5), result is undefined

letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[0..1]; // [10]
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[1..3]; // [11, 12]
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[0..5]; // [10, 11, 12, 13, 14]

letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[..3]; // [10, 11, 12]
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[3..]; // [13, 14]

letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = array[..]; // [10, 11, 12, 13, 14]

Tuple indexing

Tuples can also be indexed, though tuple indexing uses ., for example tup.0 for the leftmost tuple value. Tuple indices can only be known at compile time.

Examples

// index:                              0     1  2
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. tuple: (boolType used to represent 1 bit values, uint<2>Type used to represent unsigned integers. The generic parameter (<N>) specifReturns 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, uint<3>Type used to represent unsigned integers. The generic parameter (<N>) specifReturns 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) = (true, 3, 7);

letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = tuple.0; // true
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = tuple.1; // 3
letlet is used to define a variable. Spade infers the type of most variables from context, but you can also specifReturns 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.y the type with : <type> before the =. _ = tuple.2; // 7