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List: kde-games-devel
Subject: Re: [Kde-games-devel] Review Request 126919: Fix crash when placing bonuses in the arena
From: Mathias Kraus <k.hias () gmx ! de>
Date: 2016-01-29 19:30:15
Message-ID: 20160129193015.29981.5315 () mimi ! kde ! org
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> On Jan. 29, 2016, 11:16 a.m., Frederik Schwarzer wrote:
> > In line 354 of the same file the author already tries to handle the 4th quarter.
> > ```cpp
> > nQuarterSize = (nQuarter < 3 ? nFullSize / 4 : nFullSize - 3 * nFullSize / 4);
> > ```
> > Can you fix the issue in that line instead?
> > I mean, if I divide by 4, I am always at the lower bound of possibilities. E.g. \
> > with a size of 75, I get 18.75 mathematically, which is 18 with the '/'. If I \
> > then take three fourth of the size (size*3/4), it's 56,25, resulting in 56 being \
> > subtracted from the 75, which is 19. Boom?
> > So I would suggest something like:
> > ```cpp
> > - nQuarterSize = (nQuarter < 3 ? nFullSize / 4 : nFullSize - 3 * nFullSize \
> > / 4); + if (nQuarter < 3) {
> > + nQuarterSize = nFullSize / 4;
> > + } else {
> > + if ((nFullSize * 3 % 4) == 0) {
> > + nQuarterSize = nFullSize - nFullSize * 3 / 4;
> > + } else {
> > + nQuarterSize = nFullSize - nFullSize * 3 / 4 - 1;
> > + }
> > + }
> > ```
> > around line 354 so nQuarterSize is correct throughout the whole rest of that \
> > method.
> > Or am I barking up the wrong tree here?
>
> Mathias Kraus wrote:
> This would also fix the crash, but the solution from Julian is how it was supposed \
> to work. Because of the division by 4, the sum of the four quarters would be less \
> than nFullSize. That was the reason for the special handling of the fourth quarter, \
> which will be equal or bigger than the privious three. But the index of the fourth \
> quarter should start at the end of the third quarter, not three times the possibly \
> bigger fourth quarter, so the solution from Julian is correct.
> The solution from above will set the bonus to a block already set in quarter 3. \
> Let's assume nFullSize is a multiple of 4, e.g. 16. In this case the last quarter \
> would have a size of 3. The start index would be calculated to 9, which would be \
> part of the third quarter and could overwrite an already set bonus from m_blocks.
> The calculation of the fourth quarter is also not correct, it should be
> ```cpp
> nQuarterSize = (nQuarter < 3 ? nFullSize / 4 : nFullSize - 3 * (nFullSize / 4));
> ```
> else the last quarter will be to small. Julian, could you also fix tha and then \
> commit?
BTW, thank's Julian for looking into the problem :)
- Mathias
-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://git.reviewboard.kde.org/r/126919/#review91767
-----------------------------------------------------------
On Jan. 28, 2016, 1:30 p.m., Julian Helfferich wrote:
>
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/126919/
> -----------------------------------------------------------
>
> (Updated Jan. 28, 2016, 1:30 p.m.)
>
>
> Review request for KDE Games.
>
>
> Repository: granatier
>
>
> Description
> -------
>
> The crash takes place in game.cpp - Game::createBonus(). The total amount of blocks \
> is nFullSize. To place the bonuses, the game iterates over 4 quarters, the first \
> three containing nFullSize/4 blocks and the last containing the remaining blocks. \
> Thus, nQuarterSize can be larger for the last quarter than for the previous three. \
> Now, when a bonus is assigned to a block, the index of the block is calculated as
> nIndex = nQuarter * nQuarterSize + i
>
> where i iterates from zero to nQuarterSize. The idea is that nQuarter * \
> nQuarterSize is the number of blocks of the previous quarters. However, since \
> nQuarterSize can be larger for the last quarter, this can lead to an index out of \
> bounds when a bonus is to be placed in one of the last blocks. The fixed version is \
> nIndex = nQuarter * (nFullSize/4) + i
>
> where nFullSize/4 is the size of the first three quarters.
>
>
> Diffs
> -----
>
> src/game.cpp 371fac9
>
> Diff: https://git.reviewboard.kde.org/r/126919/diff/
>
>
> Testing
> -------
>
> Started the game a lot of times. Crash did not happen.
>
>
> Thanks,
>
> Julian Helfferich
>
>
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This is an automatically generated e-mail. To reply, visit:
<a href="https://git.reviewboard.kde.org/r/126919/">https://git.reviewboard.kde.org/r/126919/</a>
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<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <p style="margin-top: 0;">On January 29th, 2016, 11:16 a.m. UTC, <b>Frederik \
Schwarzer</b> wrote:</p> <blockquote style="margin-left: 1em; border-left: 2px solid \
#d0d0d0; padding-left: 10px;"> <pre style="white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">In line 354 of the same file the author already tries \
to handle the 4th quarter.</p> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;"><div class="codehilite" \
style="background: #f8f8f8"><pre style="line-height: 125%"> nQuarterSize <span \
style="color: #666666">=</span> (nQuarter <span style="color: #666666"><</span> \
<span style="color: #666666">3</span> <span style="color: #666666">?</span> nFullSize \
<span style="color: #666666">/</span> <span style="color: #666666">4</span> <span \
style="color: #666666">:</span> nFullSize <span style="color: #666666">-</span> <span \
style="color: #666666">3</span> <span style="color: #666666">*</span> nFullSize <span \
style="color: #666666">/</span> <span style="color: #666666">4</span>); </pre></div>
</p>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Can you fix the issue in that line instead? I mean, if \
I divide by 4, I am always at the lower bound of possibilities. E.g. with a size of \
75, I get 18.75 mathematically, which is 18 with the '/'. If I then take three fourth \
of the size (size*3/4), it's 56,25, resulting in 56 being subtracted from the 75, \
which is 19. Boom?</p> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">So I would suggest something like:</p> \
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;"><div class="codehilite" style="background: \
#f8f8f8"><pre style="line-height: 125%"><span style="color: #666666">-</span> \
nQuarterSize <span style="color: #666666">=</span> (nQuarter <span style="color: \
#666666"><</span> <span style="color: #666666">3</span> <span style="color: \
#666666">?</span> nFullSize <span style="color: #666666">/</span> <span style="color: \
#666666">4</span> <span style="color: #666666">:</span> nFullSize <span style="color: \
#666666">-</span> <span style="color: #666666">3</span> <span style="color: \
#666666">*</span> nFullSize <span style="color: #666666">/</span> <span style="color: \
#666666">4</span>); <span style="color: #666666">+</span> <span style="color: \
#008000; font-weight: bold">if</span> (nQuarter <span style="color: \
#666666"><</span> <span style="color: #666666">3</span>) { <span style="color: \
#666666">+</span> nQuarterSize <span style="color: #666666">=</span> \
nFullSize <span style="color: #666666">/</span> <span style="color: \
#666666">4</span>; <span style="color: #666666">+</span> } <span style="color: \
#008000; font-weight: bold">else</span> { <span style="color: #666666">+</span> \
<span style="color: #008000; font-weight: bold">if</span> ((nFullSize <span \
style="color: #666666">*</span> <span style="color: #666666">3</span> <span \
style="color: #666666">%</span> <span style="color: #666666">4</span>) <span \
style="color: #666666">==</span> <span style="color: #666666">0</span>) { <span \
style="color: #666666">+</span> nQuarterSize <span style="color: \
#666666">=</span> nFullSize <span style="color: #666666">-</span> nFullSize <span \
style="color: #666666">*</span> <span style="color: #666666">3</span> <span \
style="color: #666666">/</span> <span style="color: #666666">4</span>; <span \
style="color: #666666">+</span> } <span style="color: #008000; \
font-weight: bold">else</span> { <span style="color: #666666">+</span> \
nQuarterSize <span style="color: #666666">=</span> nFullSize <span style="color: \
#666666">-</span> nFullSize <span style="color: #666666">*</span> <span style="color: \
#666666">3</span> <span style="color: #666666">/</span> <span style="color: \
#666666">4</span> <span style="color: #666666">-</span> <span style="color: \
#666666">1</span>; <span style="color: #666666">+</span> }
<span style="color: #666666">+</span> }
</pre></div>
</p>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">around line 354 so nQuarterSize is correct throughout \
the whole rest of that method.</p> <p style="padding: 0;text-rendering: \
inherit;margin: 0;line-height: inherit;white-space: inherit;">Or am I barking up the \
wrong tree here?</p></pre> </blockquote>
<p>On January 29th, 2016, 7:28 p.m. UTC, <b>Mathias Kraus</b> wrote:</p>
<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;"> <pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;"><p style="padding: \
0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: inherit;">This \
would also fix the crash, but the solution from Julian is how it was supposed to \
work. Because of the division by 4, the sum of the four quarters would be less than \
nFullSize. That was the reason for the special handling of the fourth quarter, which \
will be equal or bigger than the privious three. But the index of the fourth quarter \
should start at the end of the third quarter, not three times the possibly bigger \
fourth quarter, so the solution from Julian is correct.</p> <p style="padding: \
0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: inherit;">The \
solution from above will set the bonus to a block already set in quarter 3. Let's \
assume nFullSize is a multiple of 4, e.g. 16. In this case the last quarter would \
have a size of 3. The start index would be calculated to 9, which would be part of \
the third quarter and could overwrite an already set bonus from m_blocks.</p> <p \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">The calculation of the fourth quarter is also not correct, it should be</p> \
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;"><div class="codehilite" style="background: \
#f8f8f8"><pre style="line-height: 125%">nQuarterSize <span style="color: \
#666666">=</span> (nQuarter <span style="color: #666666"><</span> <span \
style="color: #666666">3</span> <span style="color: #666666">?</span> nFullSize <span \
style="color: #666666">/</span> <span style="color: #666666">4</span> <span \
style="color: #666666">:</span> nFullSize <span style="color: #666666">-</span> <span \
style="color: #666666">3</span> <span style="color: #666666">*</span> (nFullSize \
<span style="color: #666666">/</span> <span style="color: #666666">4</span>)); \
</pre></div> </p>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">else the last quarter will be to small. Julian, could \
you also fix tha and then commit?</p></pre> </blockquote>
</blockquote>
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;"><p style="padding: \
0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: inherit;">BTW, \
thank's Julian for looking into the problem :)</p></pre> <br />
<p>- Mathias</p>
<br />
<p>On January 28th, 2016, 1:30 p.m. UTC, Julian Helfferich wrote:</p>
<table bgcolor="#fefadf" width="100%" cellspacing="0" cellpadding="12" style="border: \
1px #888a85 solid; border-radius: 6px; -moz-border-radius: 6px; \
-webkit-border-radius: 6px;"> <tr>
<td>
<div>Review request for KDE Games.</div>
<div>By Julian Helfferich.</div>
<p style="color: grey;"><i>Updated Jan. 28, 2016, 1:30 p.m.</i></p>
<div style="margin-top: 1.5em;">
<b style="color: #575012; font-size: 10pt;">Repository: </b>
granatier
</div>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" \
style="border: 1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">The crash takes place in game.cpp - \
Game::createBonus(). The total amount of blocks is nFullSize. To place the bonuses, \
the game iterates over 4 quarters, the first three containing nFullSize/4 blocks and \
the last containing the remaining blocks. Thus, nQuarterSize can be larger for the \
last quarter than for the previous three. Now, when a bonus is assigned to a block, \
the index of the block is calculated as</p> <p style="padding: 0;text-rendering: \
inherit;margin: 0;line-height: inherit;white-space: inherit;">nIndex = nQuarter * \
nQuarterSize + i</p> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">where i iterates from zero to \
nQuarterSize. The idea is that nQuarter * nQuarterSize is the number of blocks of the \
previous quarters. However, since nQuarterSize can be larger for the last quarter, \
this can lead to an index out of bounds when a bonus is to be placed in one of the \
last blocks. The fixed version is</p> <p style="padding: 0;text-rendering: \
inherit;margin: 0;line-height: inherit;white-space: inherit;">nIndex = nQuarter * \
(nFullSize/4) + i</p> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">where nFullSize/4 is the size of the \
first three quarters.</p></pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: \
1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Started the game a lot of times. Crash did not \
happen.</p></pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">
<li>src/game.cpp <span style="color: grey">(371fac9)</span></li>
</ul>
<p><a href="https://git.reviewboard.kde.org/r/126919/diff/" style="margin-left: \
3em;">View Diff</a></p>
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