(25 pts) Suppose we are compiling for a machine with 1-byte characters, 2-byte shorts, 4-byte integers, and 8-byte reals, and with alignment rules that require the address of every primitive data element to be an even multiple of the element’s size. Suppose further that the compiler is not permitted to reorder fields. How much space will be consumed by the following array? Explain.
A : array [0..9] of record
s : short
c : char
t : short
d : char
r : real
i : integer
(25 pts) For the following code specify which of the variables a,b,c,d are type equivalent under (a) structural equivalence, (b) strict name equivalence, and (c) loose name equivalence.
Type
T = array [1..10] of integer
S = T
a : T
b : T
c : S
d : array [1..10] of integer
(25 pts) We are trying to run the following C program: typedef struct
{
int a;
char * b;
} Cell;
void AllocateCell (Cell * q)
{
q = (Cell *) malloc ( sizeof(Cell) );
}
void main ()
{
Cell * c;
AllocateCell (c);
c-a = 1;
free(c);
}
The program produces a run-time error. Why?
Rewrite the functions AllocateCell and main so that the program runs correctly.
(25 pts) Consider the following C declaration, compiled on a 32-bit Pentium machine (with array elements aligned at addresses multiple of 4 bytes).
struct
{
int n; char c;
} A[10][10];
If the address of A[0][0] is 1000 (decimal), what is the address of A[3][7]? Explain how this is computed.
(Extra Credit - 10 pts) Write a small fragment of code that shows how unions can be used in C to interpret the bits of a value of one type as if they represented a value of some other type (non-converting type cast).
