From 5f02f07c763b6b22dd2136691083895b0e2547a9 Mon Sep 17 00:00:00 2001
From: Clanmaster21 <asalukehopkins@gmail.com>
Date: Wed, 9 Oct 2019 22:43:52 +0100
Subject: [PATCH] Optimised intoXX functions

Rewrote intoXX functions to mainly rely on intoHL, as the HL instructions are smaller and faster. Also removed some redundant push and pop instructions. I edited the given unit tests to test these, and they seem to work as expected.
---
 kernel/core.asm | 41 +++++++++++++++++------------------------
 1 file changed, 17 insertions(+), 24 deletions(-)

diff --git a/kernel/core.asm b/kernel/core.asm
index 9259aaa..6ffa452 100644
--- a/kernel/core.asm
+++ b/kernel/core.asm
@@ -12,7 +12,6 @@
 ; *** DATA ***
 ; Useful data to point to, when a pointer is needed.
 P_NULL:		.db 0
-
 ; *** REGISTER FIDDLING ***
 
 ; add the value of A into DE
@@ -27,34 +26,28 @@ addDE:
 noop:				; piggy backing on the first "ret" we have
 	ret
 
-; copy (DE) into DE, little endian style (addresses in z80 are always have
-; their LSB before their MSB)
-intoDE:
-	push	af
-	ld	a, (de)
-	inc	de
-	ex	af, af'
-	ld	a, (de)
-	ld	d, a
-	ex	af, af'
-	ld	e, a
-	pop	af
+; copy (HL) into HL, utilising the optimised HL instructions. The first ld
+; edits the address of the second ld to now be HL.
+intoHL:
+	ld (.load+1), hl
+.load:			
+	ld hl, (.load)		; (.load) is just a placeholder so the
+				; assembler will assemble the correct opcode
 	ret
 
-intoHL:
-	push	de
-	ex	de, hl
-	call	intoDE
-	ex	de, hl
-	pop	de
+intoDE:
+	ex de, hl
+	call intoHL
+	ex de, hl		; de not affected by intoHL, so no push/pop 
+				; is necessary
 	ret
 
 intoIX:
-	push	de
-	push	ix \ pop de
-	call	intoDE
-	push	de \ pop ix
-	pop	de
+	push ix
+	ex (sp), hl		;swap hl with ix, on the stack
+	call intoHL
+	ex (sp), hl		;restore hl from stack
+	pop ix
 	ret
 
 ; add the value of A into HL