1 files changed, 94 insertions, 0 deletions
diff --git a/PGU/CHAP4/power.s b/PGU/CHAP4/power.s
new file mode 100644
index 0000000..124586e
--- /dev/null
+++ b/PGU/CHAP4/power.s
@@ -0,0 +1,94 @@
+# 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
+
+
+
+