From 5efaead1b0f907f67941d481d7988951bf3323b4 Mon Sep 17 00:00:00 2001
From: Jeremiah Orians <jeremiah@pdp10.guru>
Date: Sun, 14 Aug 2016 15:24:37 -0400
Subject: [PATCH] Trivial prototype for strcmp function

---
 Library function prototypes/strcmp.s | 39 ++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 Library function prototypes/strcmp.s

diff --git a/Library function prototypes/strcmp.s b/Library function prototypes/strcmp.s
new file mode 100644
index 0000000..e352537
--- /dev/null
+++ b/Library function prototypes/strcmp.s	
@@ -0,0 +1,39 @@
+	# We will be using R0 and R1 to pass values to the function
+	# R15 will be used as the stack pointer
+:start
+	LOADUI R0 @string
+	COPY R1 R0
+	LOADUI R2 33
+	LOADUI R3 44
+	LOADUI R4 55
+	LOADUI R15 0x600
+	CALLI R15 @strcmp
+	HALT
+:string
+	HALT
+	NOP
+
+;;  Our simple string compare function
+:strcmp
+	;; Preserve registers
+	PUSHR R2 R15
+	PUSHR R3 R15
+	PUSHR R4 R15
+	;; Setup registers
+	MOVE R2 R0
+	MOVE R3 R1
+	LOADUI R4 0
+:cmpbyte
+	LOADXU8 R0 R2 R4			; Get a byte of our first string
+	LOADXU8 R1 R3 R4			; Get a byte of our second string
+	ADDUI R4 R4 1				; Prep for next loop
+	CMP R1 R0 R1				; Compare the bytes
+	CMPSKIP.E R0 0				; Stop if byte is NULL
+	JUMP.E R1 @cmpbyte			; Loop if bytes are equal
+;; Done
+	MOVE R0 R1					; Prepare for return
+	;; Restore registers
+	POPR R4 R15
+	POPR R3 R15
+	POPR R2 R15
+	RET R15