This lab is scheduled for 23 & 24 April.
This week we'll look at:
Begin by executing the following commands to create a directory csci/255/lab10 and copy one file into it.
The copied file is an LC-2 program that is missing a single routine. You'll write that routine.
The complete program is based on an age-old problem called the Syracuse problem. All your program really needs to do is compute the Syracuse function:
int SYR(int x) {
if (x & 1)
return 3*x + 1 ;
else
return x/2 ;
}
In most computers, it's not hard to computer x/2.
They have divide or shift right instructions. The LC-2
has neither. However, we've provided a function
DIV2 that does this for you.
All you have to do is call it.
When you run the complete program, it will prompt you for a
four hexadecimal-digit number. It will then call your
Syracuse function (SYR) over and over,
first with your input number and thereafter with the
result of the last call of the Syracuse function, until
the Syracuse function returns a one.
If you write your SYR correctly, a
run will look something like this:
Enter a four hexadecimal-digit number: 1c71 Syracuse test: 1C71 Syracuse test: 5554 Syracuse test: 2AAA Syracuse test: 1555 Syracuse test: 4000 Syracuse test: 2000 Syracuse test: 1000 Syracuse test: 0800 Syracuse test: 0400 Syracuse test: 0200 Syracuse test: 0100 Syracuse test: 0080 Syracuse test: 0040 Syracuse test: 0020 Syracuse test: 0010 Syracuse test: 0008 Syracuse test: 0004 Syracuse test: 0002 Syracuse test: 0001
It can take a while to get to 1. If your 3*X+1 overflows,
you may never get there. By the way, the 3*X+1 will
always overflow when X is
greater than or equal to 21845 (0x5555).
Your program must implement SYR
and call DIV2 using the
calling register conventions described in the
22 April lecture.
| R0 | Caller must save |
| R1 | Caller must save |
| R2 | Caller must save |
| R3 | Callee must save |
| R4 | Callee must save |
| R5 | Global pointer |
| R6 | Frame pointer |
| R7 | Return address |
All the code you add to lab10.asm will be at the very end of the file. Do not change any of the code in the first 114 lines of this file.
Don't delete your lab10.asm.