Add x86_64 asm

Signed-off-by: Carlos Maiolino <[email protected]>

1 files changed, 37 insertions, 0 deletions

diff --git a/x86_64/exponent.s b/x86_64/exponent.s
new file mode 100644
index 0000000..e469d26
--- /dev/null
+++ b/x86_64/exponent.s
@@ -0,0 +1,37 @@
+# Compute a^b, where %rbx=a and %rcx=b
+#
+# Result is added to the accumulator (%rax)
+
+
+.globl _start
+
+.section .text
+
+_start:
+	movq	$2, %rbx # Base
+	movq	$5, %rcx # Exponent
+
+	movq	$1, %rax # Initialize accumulator, take advantage of the fact
+			 # that anything to the power of 0 is 1.
+
+	# We just need to run this once, as decq will set ZF if %rcx reaches
+	# zero, and the jmp instruction does nothing with the ZF
+	cmpq	$0, %rcx
+	je	complete
+
+mainloop:
+
+	# Multiply %rbx by %rax, and stores the result in %rax
+	# Hence %rax is the accumulator register
+	mulq	%rbx
+
+	# loopq instruction is very nice, in a single instruction it does:
+	#	- decrement %rcx - The counter register -
+	#	- compare %rcx to zero
+	#	- Jump to the location specified if after decrementing %rcx is not 0
+	loopq	mainloop
+
+complete:
+	movq	%rax, %rdi
+	movq	$60, %rax
+	syscall