Merge pull request #4 from hab20002/lab2

Add Lab2

lab2/lab2.md

@@ -0,0 +1,91 @@
+# Reverse bits
+
+**Deadline:** Sunday, 2/11/2024
+
+*If you work on a lab computer, save your files to cloud storage like OneDrive.
+Otherwise, you may lose your files.*
+
+Write concise comments in code.
+
+## Learning Objectives
+
+* Logical and bit-wise operations 
+
+* Binary representation of signed integers
+
+* ASCII characters  
+
+    In order to print a newline character we will have to use the addi instruction to save the ASCII character ('\n') into a register as following:  
+  ``` addi    a0, x0, '\n' ```  
+   Now we have to do a syscall to print the ACSII character, look in the syscall tab and find the appropriate argument to print ACSII characters.
+
+## Description
+
+In this lab, we write a program in RISC-V assembly language that reverse the order
+of the bits in a register.
+
+The program reads a signed integer from the console and reverse the 32 bits in the 
+number. 
+
+Skeleton code in `lab2.s` reads an integer, using a system call, and saves it in `s1`. 
+
+Implement the following steps with RISC-V instructions.
+
+*   Write a loop to reverse the bits in `s1` and save the results in `s2`. 
+
+    Think about the strategy/algorithm first. One method is provided in
+    pseudocode at the bottom of this page. Note that we are working on bits in
+    registers and do not interprete them as signed values.  
+
+*   Use a system call to print `s1` in binary. 
+
+    Find the system call number in RARS's help. Using the syscall manual, which number represents PrintIntBinary functionality?
+
+*   Use a system call to print a newline character. 
+
+*   Use a system call to print `s2` in binary.
+
+*   Use a system call to print a newline character.   
+
+Here are some example inputs/outputs of the program. 
+
+```
+170
+00000000000000000000000010101010
+01010101000000000000000000000000
+
+20232023
+00000001001101001011011101010111
+11101010111011010010110010000000
+
+1431655765
+01010101010101010101010101010101
+10101010101010101010101010101010
+
+-3666
+11111111111111111111000110101110
+01110101100011111111111111111111
+
+-2010819982
+10001000001001010101001001110010
+01001110010010101010010000010001
+
+```
+
+## Deliverables
+
+Please submit lab2.s by the deadline.
+
+## Pseudocode 
+
+Here is one of the methods. All registers are unsigned.
+
+```
+1.  t0 = s1         // copy s1 to t0
+2.  s2 = 0
+3.  FOR (i = 0; i < 32; i += 1)  // repeat 32 times
+        // copy the the LSB in t0 to s2 
+        s2 <<= 1            // s2 = s2 << 1
+        s2 |= (t0 & 1)
+        t0 >>= 1            
+```

lab2/lab2.s

@@ -0,0 +1,22 @@
+#       CSE 3666 Lab 2
+
+        .globl  main
+
+        .text
+main:   
+        # use system call 5 to read integer
+        addi    a7, x0, 5
+        ecall
+        addi    s1, a0, 0       # copy to s1
+
+        # TODO
+        # Add you code here
+        #   reverse bits in s1 and save the results in s2
+        #   print s1 in binary, with a system call
+        #   print newline
+        #   print s2 in binary
+        #   print newline
+
+        # exit
+exit:   addi    a7, x0, 10      
+        ecall