From 985d56ca5a6bc836cf73cd3e2a4614afedb10f25 Mon Sep 17 00:00:00 2001
From: Virgil Dupras <hsoft@hardcoded.net>
Date: Tue, 23 Jul 2019 22:59:10 -0400
Subject: [PATCH] core: preserve A in cpHLDE

---
 kernel/core.asm | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/core.asm b/kernel/core.asm
index 80ca9af..9259aaa 100644
--- a/kernel/core.asm
+++ b/kernel/core.asm
@@ -84,13 +84,22 @@ subHL:
 
 ; Compare HL with DE and sets Z and C in the same way as a regular cp X where
 ; HL is A and DE is X.
+; A is preserved through some register hocus pocus: having cpHLDE destroying
+; A bit me too many times.
 cpHLDE:
+	push	bc
+	ld	b, a	; preserve A
 	ld	a, h
 	cp	d
-	ret	nz	; if not equal, flags are correct
+	jr	nz, .end ; if not equal, flags are correct
 	ld	a, l
 	cp	e
-	ret		; flags are correct
+	; flags are correct
+.end:
+	; restore A but don't touch flags
+	ld	a, b
+	pop	bc
+	ret
 
 ; Write the contents of HL in (DE)
 writeHLinDE: