Create a memory copying "wmemcpy" function that is efficient and is capable of dealing with the case where the two segments of memory (destination and source) are overlapping. This assignment will have a due date announced later. This function should fit the following prototype:
void wmemcpy ( int *srcp, int *destp, int size );
I discussed the relationships between for, while, and do while loops. A general loop will have: A beginning. A body. A branch (to beginning or end). An end. This would appear in well-structured assembly code as
# loop begins on next line loop: # beginning of the body # body instructions go here test: beq $t0,$0,loop # branch back to repeat, forward to end done: #loop has finished (end)A do-while loop will fit the above exactly. A while loop would have a jump to the test label before the beginning of the loop. A for loop would include an explicit iterator before the test, as well as an explicit initialization before the jump to the label.
I also discussed if-then statements and switch (or case) statements. Switch statements can be seen as a special case of nested if-then statements. There is a relatively common case where switch statements can be much more quickly implemented than the associated if-then sequence. To do so, the case statement should include an argument in some range that can be normalized to a sequence of integers, like (1, 2, 3, ... ). This allows the cases to be enumerated, and have their labels put into a JumpTable.
Pseudo-assembly code that would have this effect:
.data JTable: .word L0,L1,L2 .text switch: bgtu $t0,2,End # unsigned compare means negatives work too -- bsy li $t1,4 mult $s0,$t0,$t1 # ($s0 = index) gets input * 4 lw $s1, JTable($s0) jr $s1 L0: add $s2, $s2, $s3 j End L1: add $s4, $s4, $s5 j End L2: sub $s2, $s2, $s3 j End End:
Similar C code:
switch(k) {
case 0: x = x + y; break;
case 1: z = z + t; break;
case 2: x = x - y; break;
}
If I (Matt Hohlfeld) discussed anything else during this lecture, that isn't covered here, please send me mail at hohlfeld@cs.ucsd.edu.
A page for lecture 15 will be forthcoming. Since I didn't take detailed notes during lecture, if anyone with complete notes that would like to make them available to me for creating the lecture 15 page, I would greatly appreciate it.
Thank you for your attention and questions. It was fun leading class.
bsy@cse.ucsd.edu, last updated