a / 16

1 files changed, 32 insertions, 0 deletions

diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md
index 7d7afd9..3dbc306 100644
--- a/Optimizing-assembly-code.md
+++ b/Optimizing-assembly-code.md
@@ -23,6 +23,7 @@ WikiTI's advice fully applies here:
   - [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)
   - [Divide `a` by 8 (shift `a` right 3 bits)](#divide-a-by-8-shift-a-right-3-bits)
+  - [Divide `a` by 16 (shift `a` right 4 bits)](#divide-a-by-16-shift-a-right-4-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)
@@ -331,6 +332,37 @@ But do:
 ```
 
 
+### Divide `a` by 16 (shift `a` right 4 bits)
+
+Don't do:
+
+```asm
+	; 6 bytes, 9 cycles
+	; (15 bytes, at least 21 cycles, counting the definition of SimpleDivide)
+	ld c, 16 ; divisor
+	call SimpleDivide
+	ld a, b ; quotient
+```
+
+And don't do:
+
+```asm
+	; 8 bytes, 8 cycles
+	srl a
+	srl a
+	srl a
+	srl a
+```
+
+But do:
+
+```asm
+	; 4 bytes, 4 cycles
+	swap a
+	and $f
+```
+
+
 ### Set `a` to some value plus carry
 
 (The example uses `b` and `c`, but any registers besides `a` would also work, including `[hl]`.)