1 / 16

Stack and Nested Procedures

Csci136 Computer Architecture II Lab#4 - Stack and Nested Procedures - Project#1: due on Feb 13, 2005 - Quiz#1 Feb.9, 2005. Stack and Nested Procedures. Why? -may be modified by others… Must be saved before you go! Return address Local parameters Others How? -save to stacks!

tschwab
Download Presentation

Stack and Nested Procedures

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Csci136 Computer Architecture IILab#4 - Stack and Nested Procedures - Project#1: due on Feb 13, 2005 - Quiz#1Feb.9, 2005

  2. Stack and Nested Procedures • Why? -may be modified by others… • Must be saved before you go! • Return address • Local parameters • Others • How? -save to stacks! • Before you go… addi $sp,$sp, -framesize sw $ra, framesize-4($sp) # save $ra save other regs if need be • Before you return… restore other regs if need be lw $ra, framesize-4($sp) # restore $ra addi $sp,$sp, framesize jr $ra

  3. Example: Fibonacci Numbers 1/7 • Definition: F(n) = F(n – 1) + F(n – 2), F(0) and F(1) are defined to be 1. • C Programming: int fib(int n) { if(n == 0) { return 1; }   if(n == 1) { return 1; }   return (fib(n - 1) + fib(n - 2)); }

  4. Example: Fibonacci Numbers 2/7 • Now, let’s translate this to MIPS! • You will need space for three words on the stack • Why three? • Return addr($ra) • n($a0) • temp sum($s0) • Write the Prologue: # Space for three words # Save the return address # Save $s0 addi $sp, $sp, -12 sw $ra, 8($sp) sw $s0, 4($sp) fib: ___________________ ___________________ ___________________

  5. Example: Fibonacci Numbers 3/7 • Now write the Epilogue: lw $s0, 4($sp) lw $ra, 8($sp) addi $sp, $sp, 12 # Restore $s0 # Restore return address # Pop the stack frame # Return to caller fin: ___________________ ___________________ ___________________ jr $ra_____________

  6. Example: Fibonacci Numbers 4/7 • Finally, write the body. The C code is below. Start by translating the lines indicated in the comments int fib(int n) { if(n == 0) { return 1; } /*Translate Me!*/ if(n == 1) { return 1; } /*Translate Me!*/ return (fib(n - 1) + fib(n - 2)); } # $v0 = 1 # # $t0 = 1 # addi $v0, $zero, 1_ _______, _____,_fin addi $t0, $zero, 1_ _______,______,_fin Continued on next slide. . . ___________________ __if (n == 0). . . ______ ____________ __if (n == 1). . . beq $a0 $zero beq $a0 $t0

  7. Example: Fibonacci Numbers 5/7 • Finally, write the body. The C code is below. Start by translating the lines indicated in the comments int fib(int n) { … return (fib(n - 1) + fib(n - 2)); } # $a0 = n - 1 # # # # addi $a0, $a0, -1__ sw____, ___________ ___________________ lw____,____________ addi $a0, ___,_____ $a0 0($sp) jal fib $a0 0($sp) $a0, -1 Continued on next slide. . . ___________________ __Need $a0 after jal _ fib(n – 1) ______ __Restore $a0______ __$a0 = n – 2_________

  8. Example: Fibonacci Numbers 6/7 • Remember that $v0 is caller saved! int fib(int n) { . . . return (fib(n - 1) + fib(n - 2)); } # Place fib(n – 1) # somewhere it won’t get # clobbered # # add $s0,_ ___,______ ___________________ add $v0, $v0, $s0__ To the epilogue and beyond. . . _______ $v0 $zero jal fib ____________________ ____________________ ____________________ __fib(n – 2) __________ __$v0 = fib(n-1) + fib(n-2)

  9. Example: Fibonacci Numbers 7/7 • Here’s the complete code for reference fib: addi $sp, $sp, -12 sw $ra, 8($sp) sw $s0, 4($sp) addi $v0, $zero, 1 beq $a0, $zero, fin addi $t0, $zero, 1 beq $a0, $t0, fin addi $a0, $a0, -1 sw $a0, 0($sp) jal fib lw $a0, 0($sp) addi $a0, $a0, -1 add $s0, $v0, $zero jal fib add $v0, $v0, $s0 fin: lw $s0, 4($sp) lw $ra, 8($sp) addi $sp, $sp, 12 jr $ra

  10. Exercise • Show the content of the stack when computing Fib(2). • Assume the top of the stack is at address 0x7FFF and initially the stack is empty. • fib(2)=fib(1)+fib(0) • fib(1)=fib(0)=1

  11. Project#1: MergeSort • Procedure Mergesort (input A[1:n], i,j; output B[1:n]) begin Datatype C[1:n]; If i=j then B[i] = A[i]; Return; endif Mergesort (A,i,(i+j)/2;C); /* sorts the first half*/ Mergesort (A,(i+j)/2 +1,j;C); /* sorts the second half*/ Merge(C,i,j;B); /*merges the two sorted halves * *into a single sorted list */ end

  12. Project#1: MergeSort • Example:

  13. Project#1: MergeSort

  14. Quiz#1 • Give the MIPS code to load a large constant number 0xABCD9876 into register $s0. • Why not lw? • Compile the C code A[5]=A[4]+100 into MIPS code, where A is an integer array. • MIPS Addressing mode • Immediate addressing • Register addressing • Base/Displacement addressing • PC-relative addressing

  15. Quiz#1 • Specify the types of the following MIPS instructions. Describe the changes to PC after each instruction is executed. • Lw $s5, 8($sp) • Jr $31 • Beq $1, $2, 100 • J, Jr, Jal …

  16. Quiz#1 • Fast multiplication: int fmult(int a,b) { if(b == 0) { return 0; } if (even(b)) return fmult(2*a,b/2); if (odd(b)) return (a+fmult(a, b-1)); } • Use stack in your programming! • Nested Procedures

More Related