digitalmars.D.bugs - [Issue 6098] New: CTFE static array corruption of data
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http://d.puremagic.com/issues/show_bug.cgi?id=6098
Summary: CTFE static array corruption of data
Product: D
Version: D2
Platform: Other
OS/Version: Windows
Status: NEW
Severity: major
Priority: P2
Component: DMD
AssignedTo: nobody puremagic.com
ReportedBy: andrej.mitrovich gmail.com
06:15:46 PDT ---
import std.math;
import std.stdio;
import std.range;
auto makeSine(int TableSize)()
{
double[TableSize] result;
// double[] result = new double[](TableSize); // this fixes the issue
foreach (index, ref sample; result)
{
sample = cast(double)sin((cast(double)index / cast(double)TableSize) *
PI * 2.);
}
writeln(result);
return cycle(result);
}
void main()
{
auto sineTable = makeSine!(10);
writeln(take(sineTable, 10));
writeln(take(sineTable, 10));
double[] arr;
foreach (sample; take(sineTable, 10))
{
arr ~= sample;
}
writeln(arr);
}
Results:
[0, 0.587785, 0.951057, 0.951057, 0.587785, -5.42101e-20, -0.587785, -0.951057,
-0.951057, -0.587785]
[6.14906e-318, 2.59842e-307, 2.31044e-317, 0.951057, 0.587785, -5.42101e-20,
2.64149e-308, 2.08636e-317, 1.82805e-307, 2.641e-308]
[6.14906e-318, 2.59842e-307, 2.31044e-317, 2.59842e-307, 2.31044e-317,
-5.42101e-20, 2.64149e-308, 2.08636e-317, 1.82805e-307, 2.641e-308]
[6.14906e-318, 2.64128e-308, 2.49803e-307, 2.2817e-314, 6.3666e-314,
-5.42101e-20, 2.64149e-308, -nan, 1.82805e-307, 2.64126e-308]
If bugzilla makes it hard to read I've pasted the results here:
http://paste.pocoo.org/show/400027/
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Andrej Mitrovic <andrej.mitrovich gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|DMD |Phobos
Summary|CTFE static array |Static array corruption of
|corruption of data |data
06:25:49 PDT ---
Actually this has nothing to do with CTFE:
import std.math;
import std.stdio;
import std.range;
auto makeSine()
{
double[10] result;
//~ double[] result = new double[](TableSize); // this fixes the issue
foreach (index, ref sample; result)
{
sample = cast(double)sin((cast(double)index / cast(double)10) * PI *
2.);
}
writeln(result);
return cycle(result);
}
void main()
{
auto sineTable = makeSine();
writeln(take(sineTable, 10));
}
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Steven Schveighoffer <schveiguy yahoo.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |schveiguy yahoo.com
Resolution| |INVALID
06:34:16 PDT ---
Actually, it's expected :) result is on the stack, which goes away when you
return from the function (this is why the heap-allocating version has no
issues).
I'm assuming the whole shenanigans with cycle and take are so the compiler
doesn't complain? That should probably be a hint...
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http://d.puremagic.com/issues/show_bug.cgi?id=6098 06:42:45 PDT --- Smiley face, but this is a subtle thing without any warnings from the compiler. I'm using cycle here for good purpose and not to drown the compiler, take would be used to fill a buffer of some certain length. I'll just use the heap, it's not a problem. I just assumed using a range on stack-allocated data would copy the data when returning the range from the function. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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http://d.puremagic.com/issues/show_bug.cgi?id=6098 06:45:00 PDT --- Actually I can just dup manually instead of using the heap: return cycle(result.dup); -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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http://d.puremagic.com/issues/show_bug.cgi?id=6098 06:58:42 PDT ---I'm using cycle here for good purpose and not to drown the compiler, take would be used to fill a buffer of some certain length.OK, it just seemed strange that you were cycling something of length 10, and then only taking 10 elements from it. I wondered what the purpose of this was. Sorry for the assumption. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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http://d.puremagic.com/issues/show_bug.cgi?id=6098 07:16:40 PDT --- Here's a more complete example: http://paste.pocoo.org/show/400066/ Basically it's a sinewave that repeats forever. Changing the stepping will increase the pitch, the buffer length depends on the soundcard (for example the soundcard might require a couple of buffers of a certain length to be filled each second), table size basically increases the resolution or smoothness of the curve. I think that's it, anyway. I'm still new to the whole concept of audio programming. :) -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
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bearophile_hugs eml.cc changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bearophile_hugs eml.cc
Actually I can just dup manually instead of using the heap:
return cycle(result.dup);
.dup creates a copy on the heap.
This is a safer implementation:
import std.stdio, std.math, std.algorithm, std.range;
auto makeSine() {
return cycle(map!q{ sin(a * PI) }(iota(0, 2, 0.2)));
}
void main() {
auto sineTable = makeSine();
writeln(take(sineTable, 10));
}
Regarding the unsafety of the version that uses a fixed sized array, I'd like
the compiler to warn better against such bugs.
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kennytm gmail.com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |kennytm gmail.com
Actually I can just dup manually instead of using the heap:
return cycle(result.dup);
.dup creates a copy on the heap.
This is a safer implementation:
import std.stdio, std.math, std.algorithm, std.range;
auto makeSine() {
return cycle(map!q{ sin(a * PI) }(iota(0, 2, 0.2)));
}
void main() {
auto sineTable = makeSine();
writeln(take(sineTable, 10));
}
Regarding the unsafety of the version that uses a fixed sized array, I'd like
the compiler to warn better against such bugs.
This will evaluate 'sin(a * PI)' N times, which totally goes against the reason
of making a sine table. You should 'array' the 'map' before 'cycle'-ing.
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