Translation of Array References
We can access the elements of an array stored in consecutive blocks very easily and quickly. In a programming language like C and Java, the size of an array is one less than the number of the element stored in an array. We can categorize an array mainly in two types:
- One Dimensional Array
- Multi-Dimensional Array
The location of the ith element of an array ‘A’ having width ‘w’ of each array element is:
base + i * w
Here, the base is the relative address of the storage allocated for the array.
One Dimensional Array
The element of a one-dimensional array is numbered in the form of low, low + 1, and so on. We can rewrite the above formula for the ith element of an array as follows:
A[low] = base + (i – low) * w
The above expression can also be written as:
i * w + (base – low * w)
Multi-Dimensional Array
We can store the multi-dimensional array in two types:
- Row-Major
- Column-Major
Row-major: A[1, 1], A[1, 2], A[1,3], A[2, 1], A[2, 2], A[2, 3]
Column-major: A[1, 1], A[2, 1], A[1, 2], A[2, 2], A[1, 3], A[2, 3]
Translation Scheme for Array Elements
The translation scheme for an array element for the three-address statement is given below. This scheme consists of production and semantic action.
L.addr: Temporary variable
L.type: Pointer to symbol table entry for the array name
L.array: Array name
| Production Rule | Semantic Action |
| S => id = E; | L = E; | { gen ( top.get (id.lexeme) ‘=’ E.addr ); } {gen(L.array.base‘[‘ L.addr ‘]’ ‘=’ 0 E.addr ); } |
| E => E1 + E2 | id | L | {E.addr = new Temp (); gen(E.addr ‘=’ E1.addr ‘+’ E2.addr ); } {E.addr = top.get(id.lexeme ); } {E.addr = new Temp (); gen(E.addr ‘=’ L.array.base‘[‘ L.addr ‘]’);} |
| L => id [ E ] | {L.array = top.get(id.lexeme ); L.type = L.array.type.elem ; L.addr = new Temp (); gen (L.addr ‘=’ E.addr ‘*’ L.type.width ); } |
| L => L1 [ E ] | {L.array = L1.array ; L.type = L1.type .elem ; t = new Temp (); L.addr = new Temp (); gen( t ‘=’ E.addr ‘*’ L.type.width ); gen(L.addr ‘=’ L1.addr ‘+’ t ); } |
