opt

1 files changed, 123 insertions, 2 deletions

diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md
index be46820..a608c15 100644
--- a/Optimizing-assembly-code.md
+++ b/Optimizing-assembly-code.md
@@ -15,14 +15,17 @@ WikiTI's advice fully applies here:
 
 ## Contents
 
-- [Registers](#registers)
+- [8-bit registers](#8-bit-registers)
   - [Set `a` to 0](#set-a-to-0)
   - [Increment or decrement `a`](#increment-or-decrement-a)
   - [Invert the bits of `a`](#invert-the-bits-of-a)
+  - [Rotate the bits of `a`](#rotate-the-bits-of-a)
   - [Set `a` to some constant minus `a`](#set-a-to-some-constant-minus-a)
   - [Set `a` to one constant or another depending on the carry flag](#set-a-to-one-constant-or-another-depending-on-the-carry-flag)
   - [Shift `a` right by 3 bits](#shift-a-right-by-3-bits)
   - [Set `a` to some value plus carry](#set-a-to-some-value-plus-carry)
+  - [Load from HRAM to `a` or from `a` to HRAM](#load-from-hram-to-a-or-from-a-to-hram)
+- [16-bit registers](#16-bit-registers)
   - [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)
@@ -38,17 +41,19 @@ WikiTI's advice fully applies here:
   - [Compare `a` to 0](#compare-a-to-0)
   - [Compare `a` to 1](#compare-a-to-1)
   - [Compare `a` to 255](#compare-a-to-255)
+  - [Compare `a` to 0 after masking it](#compare-a-to-0-after-masking-it)
 - [Subroutines (functions)](#subroutines-functions)
   - [Tail call optimization](#tail-call-optimization)
   - [Call `hl`](#call-hl)
   - [Inlining](#inlining)
   - [Fallthrough](#fallthrough)
+  - [Conditional fallthrough](#conditional-fallthrough)
   - [Call `rst $38` depending on a flag](#call-rst-38-depending-on-a-flag)
 - [Jump and lookup tables](#jump-and-lookup-tables)
   - [Chain comparisons](#chain-comparisons)
 
 
-## Registers
+## 8-bit registers
 
 
 ### Set `a` to 0
@@ -119,6 +124,47 @@ But do:
 ```
 
 
+### Rotate the bits of `a`
+
+Don't do:
+
+```asm
+	rl a ; 2 bytes, 2 cycles
+```
+
+```asm
+	rlc a ; 2 bytes, 2 cycles
+```
+
+```asm
+	rr a ; 2 bytes, 2 cycles
+```
+
+```asm
+	rrc a ; 2 bytes, 2 cycles
+```
+
+But do:
+
+```asm
+	rla ; 1 byte, 1 cycle
+```
+
+```asm
+	rlca ; 1 byte, 1 cycle
+```
+
+```asm
+	rra ; 1 byte, 1 cycle
+```
+
+```asm
+	rrca ; 1 byte, 1 cycle
+```
+
+The exception is if you need to set the zero flag when the operation results in 0 for `a`; the two-byte operations can set `z`, the one-byte operations cannot.
+
+
 ### Set `a` to some constant minus `a`
 
 Don't do:
@@ -317,6 +363,32 @@ But do:
 ```
 
 
+### Load from HRAM to `a` or from `a` to HRAM
+
+Don't do:
+
+```asm
+	ld a, [hFoo] ; 3 bytes, 4 cycles
+```
+
+```asm
+	ld [hFoo], a ; 3 bytes, 4 cycles
+```
+
+But do:
+
+```asm
+	ldh a, [hFoo] ; 2 bytes, 3 cycles
+```
+
+```asm
+	ldh [hFoo], a ; 2 bytes, 3 cycles
+```
+
+
+## 16-bit registers
+
+
 ### Multiply `hl` by 2
 
 Don't do:
@@ -711,6 +783,23 @@ with:
 ```
 
 
+### Compare `a` to 0 after masking it
+
+Don't do:
+
+```asm
+	; 3 bytes, 3 cycles; sets zero flag if a == 0
+	and MASK
+	and a
+```
+
+But do:
+
+```asm
+	and MASK ; 2 bytes, 2 cycles; sets zero flag if a == 0
+```
+
+
 ## Subroutines (functions)
 
 
@@ -826,6 +915,38 @@ Function:
 You can still `call Function` elsewhere, but one tail call can be optimized into a fallthrough.
 
 
+## Conditional fallthrough
+
+(The example uses `z`, but `nz`, `c`, or `nc` would also work.)
+
+Don't do:
+
+```asm
+	(some code)
+	jr z, .foo
+	jr .bar
+
+.foo
+	(foo code)
+
+.bar
+	(bar code)
+```
+
+But do:
+
+```asm
+	(some code)
+	jr nz, .bar
+	; fallthrough
+.foo
+	(foo code)
+
+.bar
+	(bar code)
+```
+
+
 ### Call `rst $38` depending on a flag
 
 (The example uses `z`, but `nz`, `c`, or `nc` would also work.)