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| author | Rangi <remy.oukaour+rangi42@gmail.com> | 2020-10-06 08:35:44 -0400 |
|---|---|---|
| committer | Rangi <remy.oukaour+rangi42@gmail.com> | 2020-10-06 08:35:44 -0400 |
| commit | 61398dcd34dbcb985d71306df65ec255afb5506e (patch) | |
| tree | 839a3a3eb2dd517859c33e5d5300d30a35b24e5d /Optimizing-assembly-code.md | |
| parent | 2860eb2607fe6f2fc13decb039a3b9260811fc65 (diff) | |
Fix jr
Diffstat (limited to 'Optimizing-assembly-code.md')
| -rw-r--r-- | Optimizing-assembly-code.md | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/Optimizing-assembly-code.md b/Optimizing-assembly-code.md index a2c52d9..513f97b 100644 --- a/Optimizing-assembly-code.md +++ b/Optimizing-assembly-code.md @@ -1247,10 +1247,12 @@ But do: ```asm ; 2 bytes, 2 or 7 cycles - jr z, @ - 1 ; the byte for @ - 1 is $ff, which is the opcode for rst $38 + jr z, @ + 1 ; the byte for @ + 1 is $ff, which is the opcode for rst $38 ... ``` +(The label `@` evaluates to the current `pc` value, which in `jr z, @ + 1` is right before the `jr` instruction. The instruction consists of two bytes, the opcode and the relative offset. `@ + 1` evaluates to in-between those two bytes. The `jr` instruction encodes its offset relative to the *end* of the instruction, i.e. the *next* `pc` value after the instruction has been read, so the relative offset is `-1`, aka `$ff`.) + ## Jump and lookup tables |