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# Power Program
#
# Computes the value of a number raised to a power
# using functions.
#
# Everything in the main program is stored in registers
# no need for data section
.section .data
.section .text
.globl _start
_start:
pushq $3 # Second argument (power)
pushq $2 # First argument (base)
call power # Call the function power
# Cleanup stack removing the arguments from it
addq $16, %rsp
# Save the answer in the stack before calling power again
push %rax
pushq $2 # Second argument (Power)
pushq $5 # First argument (Base)
call power
addq $16, %rsp # Cleanup stack
# Second answer is already in %rax, get the first
# back from stack to %rdi
popq %rdi
# Just add them
addq %rax, %rdi
#Sum is already in %rdi, just call exit() with %rdi as argument
movq $60, %rax
syscall
##################
# Power Function #
##################
# - First Arg - Base power
# - Second Arg - The power to raise it to
#
# NOTE: So far, power must be 1 or greater
#
# Variables
#
# - %rbx - holds the base number
# - %rcx - holds the power (also acts as a counter)
# - -8(%rbp) holds the current result
.type power, @function
power:
pushq %rbp # Save old Base Pointer
movq %rsp, %rbp # make stack pointer the base pointer
subq $8, %rsp # Add space in stack for local storage
movq 16(%rbp), %r8 # Retrieve Base number from stack to %rbx
movq 24(%rbp), %r9 # Retrieve second argument from stack to %rcx
movq %r8, -8(%rbp) # Store current result (the operand by itself)
power_loop_start:
cmpq $1, %r9 # If power is 1, we are done
je end_power
movq -8(%rbp), %rax # Move current into %rax
imulq %r8, %rax # Multiply current result by base number
movq %rax, -8(%rbp) # Save current result
decq %r9 # Decrease the power (using as a counter)
jmp power_loop_start
end_power:
movq -8(%rbp), %rax # Retrieve end result into %rax
# Return value goes into %rax
movq %rbp, %rsp # Restore stack pointer
popq %rbp # Restore base pointer
ret
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