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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" \
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<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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