Cirrus Logic CS485 Instrukcja Użytkownika Pobierz pdf (Strona 30)

CS485G Spring 2015 30

3. The compiler knows all the offsets.

30 Linked lists

1. Example:

1 void set_val(struct rec

r, int val) {

2 while (r) {

3 int i = r->i;

4 r->y[i] = val;

5 r = r->n;

6 }

7 }

# assume d = r

# assume c = val

.L17: # loop:

movl 12(%edx), %eax # a = r->i

movl %ecx, (%edx,%eax,4) # r->y[r->i] = val

movl 16(%edx), %edx # r = r->n

testl %edx, %edx # Test r

jne .L17 # If != 0 goto loop

31 Alignment

1. Example:

1 struct S1 {

2 char c;

3 int y[2];

4 double v; // uses 8 bytes

5 }

2. The character c uses only 1 byte, so the array y starts at offset 1, and

v at offset 9.

3. But the x86 advises that n-byte primitive data should start at an ad-

dress divisible by n, that is, it should be aligned to such an address.

(a) 1 byte (char): any address

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Cirrus Logic CS485 Instrukcja Użytkownika Strona 30