Add new code

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

1 files changed, 65 insertions, 0 deletions

diff --git a/PGU/CHAP3/max_value.s b/PGU/CHAP3/max_value.s
new file mode 100644
index 0000000..7025b05
--- /dev/null
+++ b/PGU/CHAP3/max_value.s
@@ -0,0 +1,65 @@
+# 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