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Clarify

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Andy McFadden 2018-10-26 15:59:00 -07:00
parent a8af7e8794
commit 372eea385d
1 changed files with 12 additions and 8 deletions
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@ -175,8 +175,8 @@ code, but also needs to know how to handle the corner cases.</p>
and assemblers like 64tass do it the other way around. So cc65
regards the expression as <code>(label >> 8) - 16</code>, while the
more common interpretation would be <code>label >> (8 - 16)</code>.
(This is actually somewhat convenient, since many common expressions
don't require parenthesis.)</li>
(This is actually somewhat convenient, since none of the expressions
SourceGen currently generates require parenthesis.)</li>
<li>Undocumented opcodes: SBX ($cb) uses the mnemonic AXS. All other
opcodes match up with the "unintended opcodes" document.</li>
</ul>
@ -194,16 +194,20 @@ code, but also needs to know how to handle the corner cases.</p>
<p>Quirks:</p>
<ul>
<li>Operator precedence is unusual. Expressions are processed from
left to right, with no operator precedence.</li>
<li>Operator precedence is unusual. Expressions are generally processed
from left to right. The byte-selection operators have a lower
precedence than all of the others, and so are always processed last.</li>
<li>The byte selection operators ('&lt;', '&gt;', '^') are actually
word-selection operators, yielding 16-bit values when wide registers
are enabled on the 65816.</li>
<li>Values loaded into registers are implicitly mod 256 or 65536. There
is no need to explicitly mask an expression.</li>
<li>The assembler tracks register widths when it sees SEP/REP instructions,
but doesn't attempt to track the emulation flag. So if the registers
are long when you switch to emulation, incorrect code is generated.
(Really I just want to be able to turn the auto-tracking off.)</li>
<li>Non-unique local labels don't cause an error.</li>
but doesn't attempt to track the emulation flag. So if you issue a REP
while in emulation mode, the assembler will incorrectly assume long
registers. (Really I just want to be able to turn the width-tracking
off, but there's no way to do that.)</li>
<li>Non-unique local labels should cause an error, but don't.</li>
</ul>
</div>