diff options
| -rw-r--r-- | lib/xixanta/src/assembler.rs | 31 |
1 files changed, 31 insertions, 0 deletions
diff --git a/lib/xixanta/src/assembler.rs b/lib/xixanta/src/assembler.rs index c6615d2..eb4821a 100644 --- a/lib/xixanta/src/assembler.rs +++ b/lib/xixanta/src/assembler.rs @@ -1660,6 +1660,20 @@ impl<'a> Assembler<'a> { // address being referenced, which is never on the zeropage // section, so it wouldn't fit on a single byte anyways. if val.size == 1 || (val.resolved && val.bytes[1] == 0x00) { + // If despite all of the above the parsed instruction + + // zeropage indexing is actually not valid but the absolute + // indexing is, then convert this instruction to absolute + // indexing. + let mnemonic = node.value.value.to_lowercase(); + if let Some(entries) = INSTRUCTIONS.get(&mnemonic) { + if entries.get(&AddressingMode::ZeropageIndexedX).is_none() + && entries.get(&AddressingMode::IndexedX).is_some() + { + val.size = 2; + return Ok((AddressingMode::IndexedX, val)); + } + } + // Re-inforce the optimization when val.size == 2 by forcing // the size to 1. val.size = 1; @@ -1671,6 +1685,17 @@ impl<'a> Assembler<'a> { "y" => { // Same optimization as with the "x" case. if val.size == 1 || (val.resolved && val.bytes[1] == 0x00) { + // Similar to the case on "x" indexing. + let mnemonic = node.value.value.to_lowercase(); + if let Some(entries) = INSTRUCTIONS.get(&mnemonic) { + if entries.get(&AddressingMode::ZeropageIndexedY).is_none() + && entries.get(&AddressingMode::IndexedY).is_some() + { + val.size = 2; + return Ok((AddressingMode::IndexedY, val)); + } + } + val.size = 1; Ok((AddressingMode::ZeropageIndexedY, val)) } else { @@ -2360,6 +2385,9 @@ mod tests { assert_instruction("lda ($20, x)", &[0xA1, 0x20]); assert_instruction("lda ($20), y", &[0xB1, 0x20]); + // Expand zeropage-looking into absolute index. + assert_instruction("lda $42, y", &[0xB9, 0x42, 0x00]); + // ldx assert_instruction("ldx #$20", &[0xA2, 0x20]); assert_instruction("ldx $20", &[0xA6, 0x20]); @@ -2482,6 +2510,9 @@ mod tests { assert_instruction("sta ($20, x)", &[0x81, 0x20]); assert_instruction("sta ($20), y", &[0x91, 0x20]); + // Expand zeropage-looking into absolute index. + assert_instruction("sta $42, y", &[0x99, 0x42, 0x00]); + // stx assert_instruction("stx $20", &[0x86, 0x20]); assert_instruction("stx $20, y", &[0x96, 0x20]); |