[css-counter-styles-3] Rewrite the additive representation algo. This is partially for style, but also properly handles the case where you hit a 0-weight symbol when there's still value left. Fixes w3c#5784.

Author: tabatkins

css-counter-styles-3/Overview.bs

@@ -632,33 +632,33 @@ Accumulating Numerals: the ''additive'' system</h4>
 		</pre>
 	</div>
 
-	To construct the representation, run this algorithm:
+	<div algorithm="additive representation">
+		To construct the representation:
 
+		1. Let |value| initially be the counter value,
+			|S| initially be the empty string,
+			and |symbol list| initially be the list of <a>additive tuples</a>.
 
-	Let <var>value</var> initially be the counter value,
-	<var>S</var> initially be the empty string,
-	and <var>symbol list</var> initially be the list of <a>additive tuples</a>.
+		2. If |value| is 0, and there is an <a>additive tuple</a> with a weight of 0, append that tuple's <a>counter symbol</a> to |S| and return |S|.
 
-	<ol>
-		<li>If <var>value</var> is initially 0, and there is an <a>additive tuple</a> with a weight of 0, append that tuple's <a>counter symbol</a> to S and return S.
+		3. For each |tuple| in |symbol list|:
 
-		<li>While <var>value</var> is greater than 0 and there are elements left in the <var>symbol list</var>:
+			1. Let |symbol| and |weight| be |tuple|'s [=counter symbol=] and weight, respectively.
 
-			<ol>
-				<li>Pop the first <a>additive tuple</a> from the <var>symbol list</var>.
-				This is the <dfn>current tuple</dfn>.
+			2. If |weight| is zero, or |weight| is greater than |value|,
+				[=iteration/continue=].
 
-				<li>Append the <a>current tuple</a>’s <a>counter symbol</a> to <var>S</var>
-				<code>floor( <var>value</var> / <var><a>current tuple</a>’s weight</var> )</code>
-				times (this may be 0).
+			3. Let |reps| be <code>floor( |value| / |weight| )</code>.
 
-				<li>Decrement <var>value</var> by the <var><a>current tuple</a>’s weight</var> multiplied
-				by the number of times the <a>current tuple</a> was appended to <var>S</var>
-				in the previous step.
-			</ol>
+			4. Append |symbol| to |S| |reps| times.
 
-		<li>If the loop ended because <var>value</var> is 0, return S.  Otherwise, the given counter value cannot be represented by this counter style, and must instead be represented by the fallback counter style.
-	</ol>
+			5. Decrement |value| by <code>|weight| * |reps|</code>.
+				If |value| is now zero, return |S|.
+
+		4. Assertion: |value| is still non-zero.
+
+			The given counter value cannot be represented by this counter style, and must instead be represented by the fallback counter style.
+	</div>
 
 	Note: All of the predefined additive ''@counter-style'' rules in this specification
 	produce representations for every value in their range,