Question

Show the machine code corresponding to the Y86 version of the following code. Assume that the code starts at location 0x050. For each statement, list address: code bytes.

int sumInts ( long int n) { /* Add the integers from 1..n. */ long int i; long int sum = 0; for ( i = 1; i <= n; i++ ) { sum += i; } return sum; }

Answer 1

Assembly code :

sumInts:
1       irmovl $0,eax           # sum = 0
2       irmovl $1,ebx           # i = 1
Loop:
3       rrmovl %esp,%edx       # %esp = n; counter(%edx) = n ; to compare with i for looping
4       addl %ebx,%eax           # sum = sum + i
5       irmovl $1,%ecx
6       addl %ecx,%ebx           # i = i+1
7       subl %ebx,%edx           # counter = counter - i ; it becomes negative when i = n+1
8       jl Loop                   # if counter >= 0, goto Loop
9       ret                       # return when counter < 0

Corresponding machine code by line numbers as mentioned above assuming code starts at 0x050 :

1 0x050   : 30F000000000
2 0x056 : 30F100000001
3 0x05C : 2042
4 0x05F : 6010
5 0x061 : 30F200000001
6 0x067 : 6021
7 0x069 : 6113
8 0x06B : 720000005C
9 0x070 : 90