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01f59fa85f
heavily customized version of DUMB (Dynamic Universal Music Bibliotheque).
It has been slightly modified by me:
* Added support for Ogg Vorbis-compressed samples in XM files ala FMOD.
* Removed excessive mallocs from the replay core.
* Rerolled the loops in resample.c. Unrolling them made the object file
~250k large while providing little benefit. Even at ~100k, I think it's
still larger than it ought to be, but I'll live with it for now.
Other than that, it's essentially the same thing you'd hear in foobar2000,
minus some subsong detection features. Release builds of the library look
like they might even be slightly faster than FMOD, which is a plus.
- Fixed: Timidity::font_add() did not release the file reader it created.
- Fixed: The SF2 loader did not free the sample headers in its destructor.
SVN r995 (trunk)
129 lines
5.1 KiB
Text
129 lines
5.1 KiB
Text
/* _______ ____ __ ___ ___
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* \ _ \ \ / \ / \ \ / / ' ' '
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* | | \ \ | | || | \/ | . .
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* | | | | | | || ||\ /| |
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* | | | | | | || || \/ | | ' ' '
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* | | | | | | || || | | . .
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* | |_/ / \ \__// || | |
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* /_______/ynamic \____/niversal /__\ /____\usic /| . . ibliotheque
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* / \
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* / . \
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* ptr.txt - Pointer explanation. / / \ \
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* | < / \_
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* | \/ /\ /
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* \_ / > /
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* | \ / /
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* | ' /
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* \__/
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*/
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A pointer is a small variable (often the same size as an int BUT NOT ALWAYS)
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that holds the address of something in memory. You create a pointer by adding
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a * to a variable, as follows:
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int x, *y;
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x = 5;
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y = &x;
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The & means 'address of', so &x gives us a pointer to x. We are storing it in
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y.
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(*y)++;
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The * here means 'value at'. It's known as the 'dereferencing' operator. When
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written before a pointer, as it is here, it allows you to treat the value
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like a normal variable. In this case we are incrementing the value. If we
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look at x, we'll find that it now contains 6, not 5.
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y++;
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Here we are incrementing the pointer itself. This is useful for traversing
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through an array, but in this particular example it is not much use.
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*y++;
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Beware; this will increment the pointer, not the value stored there. It will
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return the value stored at the pointer (before incrementing the pointer), so
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you can use this in a bigger expression. This is why we needed brackets in
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the first example.
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Note that you will not need these three examples when working with DUMB; they
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are simply to help illustrate the idea of pointers.
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Also be aware that when defining pointers you attach the * to the variable,
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not to the type. The following example will create a pointer and an int, not
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two pointers:
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int *a, b;
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That is why I believe it's a good idea to put a space before the * and not
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after it, although programmers are divided on this.
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y = 0;
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y = NULL;
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These two statements are equivalent. 0, or NULL, is a special value that is
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guaranteed to have a different value from any valid pointer. This is most
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often used to indicate that something doesn't point anywhere. DUMB's
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functions may return it on occasion. However, in simple usage of DUMB, you
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will not actually need to check for it.
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Some of DUMB's functions return pointers to structs. (A struct is an
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aggregration of other variables, such as ints, pointers, or other structs.
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You can generally treat a struct as a single unit.) Here's an example of such
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a function:
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DUH *dumb_load_it(const char *filename);
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You do not know what the DUH struct actually contains; dumb.h and aldumb.h
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only give the compiler enough information to deal with pointers to them. DUMB
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will take charge of everything that happens inside a DUH struct.
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The above function will create a DUH struct for you. First it allocates
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the memory it needs, then it fills the struct with data, then it returns a
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pointer. This DUH struct will contain the data necessary to play an IT file.
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You can define a suitable variable and store the pointer in it as follows:
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DUH *duh = dumb_load_it("music.it");
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Or this can be split up:
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DUH *duh;
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duh = dumb_load_it("music.it");
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In order to use this DUH struct later, you must pass its pointer to other
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functions. To pass the pointer to a function, simply write 'duh' for the
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appropriate parameter.
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When you've finished with a DUH struct (this applies equally to the other
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structs DUMB deals with), you must pass it to an appropriate function for
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freeing up the memory:
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unload_duh(duh);
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After you've done this, the memory will no longer be allocated, and the
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pointer will have no meaning. You may wish to set it to NULL at this point
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for safety. Alternatively just be sure not to use the present value of the
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pointer any more. You can of course assign a new value to the pointer, e.g.
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by calling dumb_load_it() again.
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Note the following:
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DUH *duh2 = duh;
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This only duplicates the pointer, not the DUH itself. You still only have one
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copy of the DUH. There is no way of duplicating a DUH, short of loading it
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twice. This is not a problem, because DUMB can play it 'twice at the same
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time' anyway.
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That should be all you need to know about pointers in order to use DUMB. If
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there's anything you feel should be explained better here, or anything else
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that should be added, please don't hesitate to let me know!
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Ben Davis
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entheh@users.sf.net
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IRC EFnet #dumb
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See readme.txt for details on using IRC.
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