From 2224a9264efafcfece76d6d1fc4e8751e6e92492 Mon Sep 17 00:00:00 2001
From: Clanmaster21 <asalukehopkins@gmail.com>
Date: Sun, 13 Oct 2019 18:45:28 +0100
Subject: [PATCH] Corrected error in comments, and a new parseHex

5 bytes saved in parseHex, again hard to say what that does to speed, the shortest possible speed is probably a little slower but I think non-error cases should be around 9 cycles faster for decimal and 18 cycles faster for hex as there's now only two conditional returns and no compliment carries.
---
 kernel/parse.asm | 20 +++++++++-----------
 1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/kernel/parse.asm b/kernel/parse.asm
index 9c97992..fda3a6e 100644
--- a/kernel/parse.asm
+++ b/kernel/parse.asm
@@ -11,23 +11,21 @@
 ; On success, the carry flag is reset. On error, it is set.
 parseHex:
 	; First, let's see if we have an easy 0-9 case
-	sub	'0'
-	ret	c
-	cp	10
-	ccf
+	
+	add 	a, 0xc6	; maps '0'-'9' onto 0xf6-0xff
+	sub 	0xf6	; maps to 0-9 and carries if not a digit
 	ret	nc
 
 .alpha:
-	and 	0xdf		; converts uppercase to lowercase
-	sub	0x11		; C if <'A'
-	ret	c
-	cp	6		; not C if >'F'
-	ccf
-	ret	c
+	and 	0xdf		; converts lowercase to uppercase
+	add	0xe9		; map 0x11-x017 onto 0xFA - 0xFF
+	sub 	0xfa		; map onto 0-6
+	ret 	c
 	; We have alpha.
-	add	a, 10		; C is clear
+	add	a, 10		; C is clear, map back to 0xA-0xF
 	ret
 
+
 ; Parses 2 characters of the string pointed to by HL and returns the numerical
 ; value in A. If the second character is a "special" character (<0x21) we don't
 ; error out: the result will be the one from the first char only.