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# Find the maximum value inside a static list
# Variables used:
#
# - %r11 - Holds index of the data item being examined
# - %rdi - Largest data item found so far
# - %rax - Current data item
#
#
# Constant memory locations:
#
# data_items - contains the item data. (Marks the beginning actualy)
# So far, 0 is used as terminator
#
# This program is written for x86_64 processors, it won't assemble in x86
.section .data # Specify data section
# Array of data items. This use 8bytes (quad-word) for each location
data_items:
.quad 133,55,50,12,25,77,30,93,222,55,62,250,66,34,69,0
.section .text
# Mark program's starting point so Linux can 'see' it
.globl _start
_start:
movq $0, %r11 # Move 0 into %rdi to indicate
# the start of the index
movq data_items(,%r11,8), %rax # Load the first data item (8bytes long)
# This actually uses indexed access
# mode, where %rdi is the 'offset' into
# the data_items array, and 8 is the
# multiplier.
movq %rax, %rbx # This is the first item, so, %rax is
# current the biggest anyway
# Loop over all items
start_loop:
cmpq $0, %rax # compare current item with the
je loop_exit # terminator 0, and jump to exit
# if it is equal.
incq %r11 # Increment index so we can grab next
# item
movq data_items(,%r11,8), %rax # Grab next item once we incremented the
# index above
cmpq %rbx, %rax # If our current item in %rax is smaller
jle start_loop # we ignore it and move back to the loop
movq %rax, %rdi # Otherwise we store it as our new largest
jmp start_loop # item and jump back to the loop unconditionally
loop_exit:
movq $60, %rax # Call exit() syscall, our argument is
# already in %rdi, just setup syscall
syscall # number and call kernel
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