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| -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 |