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LibWeb: Avoid division by zero when computing table measures

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For malformed tables which only have cells with span greater than 1, the
content sizes for row and column aren't initialized to non-zero values.
Avoid undefined behavior in such cases, which sometimes show up on
Wikipedia.
This commit is contained in:
Andi Gallo 2023-07-27 00:43:26 +00:00 • committed by Andreas Kling
parent 47595b9ef0
commit 3b75b9ef1c
3 changed files with 39 additions and 4 deletions
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24
Tests/LibWeb/Layout/expected/table/avoid-div-by-zero-in-table-measures.txt Normal file
View file

@ -0,0 +1,24 @@
Viewport <#document> at (0,0) content-size 800x600 children: not-inline
BlockContainer <html> at (0,0) content-size 800x600 [BFC] children: not-inline
BlockContainer <body> at (8,8) content-size 784x23.46875 children: not-inline
TableWrapper <(anonymous)> at (8,8) content-size 6x23.46875 [BFC] children: not-inline
Box <table> at (8,8) content-size 6x23.46875 table-box [TFC] children: not-inline
BlockContainer <(anonymous)> (not painted) children: inline
TextNode <#text>
Box <tbody> at (8,8) content-size 0x19.46875 table-row-group children: not-inline
BlockContainer <(anonymous)> (not painted) children: inline
TextNode <#text>
Box <tr> at (10,10) content-size 0x19.46875 table-row children: not-inline
BlockContainer <(anonymous)> (not painted) children: inline
TextNode <#text>
BlockContainer <td> at (11,11) content-size 0x17.46875 table-cell [BFC] children: inline
line 0 width: 14.265625, height: 17.46875, bottom: 17.46875, baseline: 13.53125
frag 0 from TextNode start: 0, length: 1, rect: [11,11 14.265625x17.46875]
"A"
TextNode <#text>
BlockContainer <(anonymous)> (not painted) children: inline
TextNode <#text>
BlockContainer <(anonymous)> (not painted) children: inline
TextNode <#text>
BlockContainer <(anonymous)> (not painted) children: inline
TextNode <#text>

7
Tests/LibWeb/Layout/input/table/avoid-div-by-zero-in-table-measures.html Normal file
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@ -0,0 +1,7 @@
<table>
<tbody>
<tr>
<td colspan="2">A</td>
</tr>
</tbody>
</table>

4
Userland/Libraries/LibWeb/Layout/TableFormattingContext.cpp
View file

@ -495,8 +495,10 @@ void TableFormattingContext::compute_table_measures()
// the product of:
// - the ratio of the max-content size based on cells of span up to N-1 of the column to the baseline max-content size
// - the outer min-content size of the cell minus the baseline max-content size and baseline border spacing, or 0 if this is negative
if (baseline_max_content_size != 0) {
cell_min_contribution += (rows_or_columns[rc_index].max_size / static_cast<double>(baseline_max_content_size))
* max(CSSPixels(0), cell_min_size<RowOrColumn>(cell) - baseline_max_content_size - baseline_border_spacing);
}
// The contribution of the cell is the sum of:
// the max-content size of the column based on cells of span up to N-1
@ -504,8 +506,10 @@ void TableFormattingContext::compute_table_measures()
// and the product of:
// - the ratio of the max-content size based on cells of span up to N-1 of the column to the baseline max-content size
// - the outer max-content size of the cell minus the baseline max-content size and the baseline border spacing, or 0 if this is negative
if (baseline_max_content_size != 0) {
cell_max_contribution += (rows_or_columns[rc_index].max_size / static_cast<double>(baseline_max_content_size))
* max(CSSPixels(0), cell_max_size<RowOrColumn>(cell) - baseline_max_content_size - baseline_border_spacing);
}
cell_min_contributions_by_rc_index[rc_index].append(cell_min_contribution);
cell_max_contributions_by_rc_index[rc_index].append(cell_max_contribution);
}