# Illustration of Intel string instructions.

# The STOS (STOre String) family of instructions do an extremely fast
# copy of a given string to a bunch of consecutive memory locations,
# much faster than one could do with MOV instructions in a programmer-
# written loop.

# The stosl instruction copies the word in EAX to the memory word
# pointed to by the EDI register, and increments EDI by 4.

# If we add the "prefix" rep, this effectively becomes the equivalent of
# a loop:  The stosl instruction will be executed repeatedly, with ECX
# being decremented by 1 each time, until ECX reaches 0.  Note that the
# rep is in effect an extra op code, prepended before the instruction
# itself.

# EDI, EAX and ECX are wired-in operands for this instruction.  The
# programmer has no option here, and thus they do not appear in the
# assembly code.  The way to remember EDI is that the D stands for
# "destination."

# The STOS family of instructions includes 4-byte, 2-byte and 1-byte
# versions.  The latter two use AX and AL for the source string,
# respectively, and in AT&T syntax are named stos and stosb.

# There is also the MOVS family, which copies one possibly very long
# string in memory to another place in memory.  EDI again plays the
# destination role, i.e. points to the place to be copied to, and the
# ESI resgister points to the source string.

.data
x: 
     .space 20  # set up 5 words of space

.text

.globl _start

_start:
      movl $x,%edi
      movl $5,%ecx  # we will copy our string to 5 words
      movl $0x12345678,%eax  # the string to be copied is 0x12345678
      rep stosl
done: