Opt

1 files changed, 39 insertions, 48 deletions

diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md
index f45a44a..2cc248a 100644
--- a/Optimizing-assembly-code.md
+++ b/Optimizing-assembly-code.md
@@ -7,30 +7,29 @@ Most of these tricks come from either [Jeff's GB Assembly Code Tips v1.0](http:/
 
 - [Registers](#registers)
   - [Set `a` to 0](#set-a-to-0)
-  - [Set `a` to some constant minus `a`](#set-a-to-some-constant-minus-a)
   - [Invert the bits of `a`](#invert-the-bits-of-a)
+  - [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)
-  - [Increment a 16-bit register](#increment-decrement-a-16-bit-register)
+  - [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)
   - [Load two constants into a register pair](#load-two-constants-into-a-register-pair)
   - [Load a constant into `[hl]`](#load-a-constant-into-hl)
-  - [Load a constant into `[hl]` and increment or decrement `hl`](#load-a-constant-into-hl-and-increment-or-decrement-hl)
+  - [Load a constant into `[hl]` and incrementing or decrementing `hl`](#load-a-constant-into-hl-and-incrementing-or-decrementing-hl)
   - [Increment or decrement `[hl]`](#increment-or-decrement-hl)
 - [Branching (control flow)](#branching-control-flow)
   - [Relative jumps](#relative-jumps)
   - [Compare `a` to 0](#compare-a-to-0)
   - [Compare `a` to 1](#compare-a-to-1)
   - [Compare `a` to 255](#compare-a-to-255)
-  - [Add `a` to `hl` without using a 16-bit register](#add-a-to-hl-without-using-a-16-bit-register)
 - [Subroutines (functions)](#subroutines-functions)
   - [Tail call optimization](#tail-call-optimization)
   - [Call `hl`](#call-hl)
   - [Inlining](#inlining)
   - [Fallthrough](#fallthrough)
 - [Jump and lookup tables](#jump-and-lookup-tables)
-  - [Chain comparisons](#chaining-comparisons)
+  - [Chain comparisons](#chain-comparisons)
 
 
 ## Registers
@@ -66,38 +65,38 @@ Don't use the optimized versions if you need to preserve flags. As such, `ld a,
 ```
 
 
-### Set `a` to some constant minus `a`
+### Invert the bits of `a`
 
 Don't do:
 
 ```asm
-	; 4 bytes, 4 cycles
-	ld b, a
-	ld a, CONST
-	sub b
+	xor $ff ; 2 bytes, 2 cycles
 ```
 
 But do:
 
 ```asm
-	; 3 bytes, 3 cycles
-	cpl
-	add CONST + 1
+	cpl ; 1 byte, 1 cycle
 ```
 
 
-### Invert the bits of `a`
+### Set `a` to some constant minus `a`
 
 Don't do:
 
 ```asm
-	xor $ff ; 2 bytes, 2 cycles
+	; 4 bytes, 4 cycles
+	ld b, a
+	ld a, CONST
+	sub b
 ```
 
 But do:
 
 ```asm
-	cpl ; 1 byte, 1 cycle
+	; 3 bytes, 3 cycles
+	cpl
+	add CONST + 1
 ```
 
 
@@ -150,7 +149,7 @@ and don't do:
 But do:
 
 ```asm
-	; 5 bytes, 5 cycles
+	; 5 bytes, 5 or 6 cycles
 	add l
 	ld l, a
 	jr nc, .no_carry
@@ -159,19 +158,28 @@ But do:
 .no_carry:
 ```
 
-Or better (doesn't require a label):
+Or better, do:
 
 ```asm
 	; 5 bytes, 5 cycles
-	add l ; = a + l
-	ld l, a ; cache a + l
-	adc h ; = a + l + carry + h
-	sub l ; = carry + h
+	add l
+	ld l, a
+	adc h
+	sub l
 	ld h, a
 ```
 
+Or if you can spare another 16-bit register and want to optimize for size over speed, do:
+
+```asm
+	; 4 bytes, 5 cycles
+	ld d, 0
+	ld e, a
+	add hl, de
+```
+
 
-### Increment / decrement a 16-bit register
+### Increment or decrement a 16-bit register
 
 When possible, avoid doing:
 
@@ -179,13 +187,19 @@ When possible, avoid doing:
 	inc hl ; 1 byte, 2 cycles
 ```
 
-If you can ensure that the low byte won't overflow (or that it won't matter if it does), then do this:
+```asm
+	dec hl ; 1 byte, 2 cycles
+```
+
+If the low byte won't overflow, then do:
 
 ```asm
 	inc l ; 1 byte, 1 cycle
 ```
 
-Further, if you intend your code to run on DMG (black & white GB), avoiding 16-bit inc/dec means less occasions to trigger the OAM corruption bug.
+```asm
+	dec l ; 1 byte, 1 cycle
+```
 
 
 ### Load from an address to `hl`
@@ -451,29 +465,6 @@ with:
 ```
 
 
-### Add `a` to `hl` without using a 16-bit register
-
-Don't do:
-
-```asm
-	; 4 bytes, 5 cycles
-	ld d, 0
-	ld e, a
-	add hl, de
-```
-
-But do:
-
-```asm
-	; 5 bytes, 5 or 6 cycles
-	add l
-	ld l, a
-	jr nc, .no_carry
-	inc h
-.no_carry
-```
-
-
 ## Subroutines (functions)