More optimal code

1 files changed, 27 insertions, 0 deletions

diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md
index 80d83a6..325798a 100644
--- a/Optimizing-assembly-code.md
+++ b/Optimizing-assembly-code.md
@@ -11,6 +11,7 @@ Most of these tricks come from either [Jeff's GB Assembly Code Tips v1.0](http:/
   - [Set `a` to some constant minus `a`](#set-a-to-some-constant-minus-a)
   - [Multiply `hl` by 2](#multiply-hl-by-2)
   - [Add `a` to a 16-bit register](#add-a-to-a-16-bit-register)
+  - [Add `a` to an address](#add-a-to-an-address)
   - [Increment or decrement a 16-bit register](#increment-or-decrement-a-16-bit-register)
   - [Load from an address to `hl`](#load-from-an-address-to-hl)
   - [Exchange two 16-bit registers](#exchange-two-16-bit-registers)
@@ -118,6 +119,7 @@ But do:
 
 (The `SpeciesItemBoost` routine in [engine/battle/effect_commands.asm](../../blob/master/engine/battle/effect_commands.asm#L2812-L2814) actually does this!)
 
+
 ### Add `a` to a 16-bit register
 
 (The example uses `hl`, but `bc` or `de` would also work.)
@@ -176,6 +178,31 @@ Or if you can spare another 16-bit register and want to optimize for size over s
 	add hl, de
 ```
 
+### Add `a` to an address
+
+(The example uses `hl`, but `bc` or `de` would also work.)
+
+Don't do:
+
+```asm
+	; 7 bytes, 8 cycles; uses another 16-bit register
+	ld e, a
+	ld d, 0
+	ld hl, Address
+	add hl, de
+```
+
+But do:
+
+```asm
+	; 7 bytes, 7 cycles
+	add a, LOW(Address)
+	ld l, a
+	adc a, HIGH(Address)
+	sub l
+	ld h, a
+```
+
 
 ### Increment or decrement a 16-bit register