1 files changed, 48 insertions, 0 deletions
diff --git a/3/8_array_allocation_and_access/40_diagonal_elements.c b/3/8_array_allocation_and_access/40_diagonal_elements.c
new file mode 100644
index 0000000..ab541db
--- /dev/null
+++ b/3/8_array_allocation_and_access/40_diagonal_elements.c
@@ -0,0 +1,48 @@
+// A in rdi, val in rsi
+//  fix_set_diag:
+//      movl    $0, %eax
+//  .L13
+//      movl    %esi, (%rdi, %rax)
+//      addq    $68, %rax
+//      cmpq    $1088, %rax
+//      jne     .L13
+//      rep; ret
+#include <stdio.h>
+#define N 16
+typedef int fix_matrix[N][N];
+
+void fix_set_diag(fix_matrix A, int val) {
+    long i;
+    for (i = 0; i < N; i++) {
+        A[i][i] = val;
+    }
+}
+
+void fix_set_diag_opt(fix_matrix A, int val) {
+    int *Aptr = &A[0][0];
+    int *Aend = &A[N][N];
+    do {
+        *Aptr = val;
+        Aptr += N; // Next row
+        Aptr ++; // Next column
+    } while (Aptr != Aend);
+}
+
+int main(void) {
+    int i, j;
+    fix_matrix A;
+    for (i=0; i < N; i++) {
+        for (j=0; j < N; j++) {
+            A[i][j] = 0;
+        }
+    }
+
+    i, j = 0, 0;
+    fix_set_diag_opt(A, 1);
+    for (i=0; i < N; i++) {
+        for (j=0; j < N; j++) {
+            printf("%ld", A[i][j]);
+        }
+        printf("\n");
+    }
+}