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| -rw-r--r-- | Optimizing-assembly-code.md | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md index f6e4651..8a90e9e 100644 --- a/Optimizing-assembly-code.md +++ b/Optimizing-assembly-code.md @@ -21,6 +21,7 @@ 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) - [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) - [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) @@ -233,6 +234,47 @@ But do: ``` +### Set `a` to some value plus carry + +(The example uses `b` and `c`, but any registers besides `a` would also work, including `[hl]`.) + +Don't do: + +```asm + ; 4 bytes, 4 cycles + ld b, a + ld a, c + adc 0 +``` + +But do: + +```asm + ; 3 bytes, 3 cycles + ld b, a + adc c + sub b +``` + +And don't do: + +```asm + ; 5 bytes, 5 cycles + ld b, a + ld a, N + adc 0 +``` + +But do: + +```asm + ; 4 bytes, 4 cycles + ld b, a + adc N + sub b +``` + + ### Multiply `hl` by 2 Don't do: |