Optimize hl|bc|de = Foo + a

1 files changed, 26 insertions, 0 deletions

diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md
index b3453b4..d2fafc2 100644
--- a/Optimizing-assembly-code.md
+++ b/Optimizing-assembly-code.md
@@ -177,6 +177,8 @@ The exception is if you need to set the zero flag when the operation results in
 
 (This optimization is from [Retro Programming](http://www.retroprogramming.com/2014/01/fast-z80-bit-reversal.html)).
 
+(The example uses `b` and `c`, but any of `d`, `e`, `h`, or `l` would also work.)
+
 Don't do:
 
 ```asm
@@ -769,6 +771,30 @@ Don't do:
 	add hl, de
 ```
 
+And don't do:
+
+```asm
+	; 8 bytes, 8 cycles
+	ld hl, Address
+	add l
+	ld l, a
+	adc h
+	sub l
+	ld h, a
+```
+
+And don't do:
+
+```asm
+	; 8 bytes, 7 or 8 cycles
+	ld h, HIGH(Address)
+	add LOW(Address)
+	ld l, a
+	jr nc, .no_carry
+	inc h
+.no_carry
+```
+
 But do:
 
 ```asm