23 Mar, 2016 @ 23:27

After having so much fun with the last Euler Problem I have taken on the second one. I plan to do atleast 2 or 3 a week and try to get them submitted here for anyone to be able to see.

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...

By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

This problem was good fun, but being new back at ASM it proved some fun challenges which got me using the DDD debugger frontend for GDB. Matching pop's with pushes turned out to be the problem and I focused alot on refactoring so not as many were required, with all the *jmp* you have to be very focused on the stack flow.

And finally probably what everyone is waiting for, the code!

# https://projecteuler.net/problem=2 # Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 # and 2, the first 10 terms will be: # 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ... # # By considering the terms in the Fibonacci sequence whose values do not exceed four million, # find the sum of the even-valued terms. # # Solution by Joseph Mullins # Answer: 4613732 # # Compile with gcc euler_2.s .global main .text main: mov $1, %rax # The first number mov $1, %rbx # The second number xor %rcx, %rcx # The result xor %rdx, %rdx # The total loop: mov %rax, %rcx # move first number into result add %rbx, %rcx # add second number to the result push %rax # Store everything push %rbx push %rdx mov $0, %rdx mov %rcx, %rax mov $2, %rbx # set up to divide by 2 to see if even div %rbx cmp $0, %rdx # if remainder is 0 then it was even so jump to add_to_total je add_to_total pop %rdx # If wasnt even, repopulate the registers, remembering the ordering we stacked them pop %rbx pop %rax push %rcx # we need rcx later to see if the term value is over 4,000,000 mov %rbx, %rcx # Store second number, add first number to it then put stored number into first number add %rax, %rbx mov %rcx, %rax pop %rcx # Retrieve rcx cmp $4000000, %rcx # compare if terms are over 4,000,000, if so jmp to print or repeat jnb print jmp loop add_to_total: pop %rdx # restore total add %rcx, %rdx # add to total pop %rbx # restore old values pop %rax mov %rbx, %rcx # Store second number, add first number to it then put into first number add %rax, %rbx mov %rcx, %rax jmp loop print: mov $format, %rdi # set first paramter of print f, formatting mov %rdx, %rsi # set 2nd paramter (the result) xor %rax, %rax # because printf is varargs call printf ret format: .asciz "%200d\n"

Answer: 4613732

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