Cirrus Logic CS485 Bedienungsanleitung PDF herunterladen (Seite 29)

CS485G Spring 2015 29

8. Lecture 16, 2/25/2015

9. General addressing case: T A[R][C]; deﬁnes a two-dimensional

array of type T with R rows and C columns. Say type T requires k

bytes. Then the location of A[i][j] is A + kiR + kj = A + k(iR + j).

10. Example:

1 int getElement(int n, int x[n][n], int i, int j) {

2 return a[i][j];

3 }

movl 8(%ebp), %eax # n (param 1)

sall $2, %eax # a = 4n

movl %eax, %edx # d = 4n

imull 16(%ebp), %edx # d = 4 n

movl 20(%ebp), %eax # a = j (param 4)

sall $2, %eax # a = 4j

addl 12(%ebp), %eax # a = x + 4j

movl (%eax,%edx), %eax # a =

(x + 4j + 4n

11. Walking down a column can be optimized by computing the address

of the ﬁrst element in the column, then repeatedly adding the stride

(the number of bytes per row).

29 Structures

1. A struct is a contiguously allocated region of memory with named

ﬁelds. Each ﬁeld has its own type.

2. Example:

1 struct rec {

2 int y[3];

3 int i;

4 struct rec

5 };

Memory layout of rec, starting at address x, is based on offsets:

y x

i x+12

n x+16

end x+20

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Cirrus Logic CS485 Bedienungsanleitung Seite 29