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Overview
This page has some useful links for the MinGW C compiler and lists some
useful information/tips that I've learned about using MinGW. Click on
any of the links in the left (blue) or right (green) tables.
Starter Links and References
There are several good links to MinGW documentation at the
MinGW site. Advanced users
can quickly find answers to many technical questions by searching through the
MinGW
users mail archive.
For introductions, try
Colin Peters' Programming
Win32 with GNU C and C++ page, and
Mike Linkovich's MinGW
Startup Guide.
Other good references are Matt Daws'
All about
MinGW page (Matt has a very interesting set of pages
in general) and Mumit Khan's
GNU
Win32 Related Projects page for integrated development environments
(IDE's) and other tools that work with Cygwin32.
A development environment
for MinGW can be obtained from the folks at
bloodshed.net.
Compile Flags
I do a lot of numeric (double precision floating point) programming, and
my experience is that the -O3 -ffast-math compile flag combination
consistently yields just about the best result. Be warned that
-ffast-math
takes some math shortcuts and does not follow all IEEE error-handling
conventions, so if you use this flag, you should verify your results,
especially if you need very high accuracy. My experience is that it
is well worth the speed boost to use this flag. I have seen on the
MinGW users mail archive that
-Os (optimize for small code size) can
also yield the best results in some cases, perhaps because it allows the
code to fit better into the CPU's L1 or L2 cache. I also prefer to
use the -Wall flag
to report all warnings. This is an excellent practice.
Some Fast Math Functions
When MinGW's
pow function became 10x slower in release 3.0 and caused some of my
codes which used it heavily to become much slower, I started investigating
ways to implement some faster math functions. I first patched the 3.0
pow() function to go back to how it was in 2.0, but then I decided to
be more aggressive.
The floating point unit in most modern Intel and AMD CPU's (e.g. Pentiums
and Athlons) has many built-in transcendental functions such as sine,
cosine, arc-tangent, etc. These built-ins are automatically used by
the Microsoft C run-time library DLL which MinGW links to by default,
but making calls to the DLL typically incurs significant overhead.
You can use the header file here to in-line some of these functions
for faster performance on Pentiums and Athlons. It requires use of
the -ffast-math compile flag. I took
some of the code from Chapter 14 (pp. 807-808) of the Art of Assembly
Language link below. Note that the exp() and atan2() in-line versions
are actually slower on a 64-bit Opteron compile (SuSE Linux 8.0).
Also note that these in-line functions do not do any error
checking or trapping of any kind.
NOTE! My in-line pow() function now returns correct
results if the first argument is zero (Rev 1.01).
NOTE 2! GCC
v4.0 will include a more complete set of fast math intrinsics for
x87-compatible processors, including fsincos.
x87inline.h
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x87test.c
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Art of Assembly
In-line
Assy How-To
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In-line
Assy Linux Docs
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Gnu C In-line Assy docs
Results: PIII
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P4 Xeon
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Opteron (32-bit)
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Opteron (64-bit)
MinGW and Win32 DLLs
A very cool feature in MinGW is that you can put
DLL files directly in the compile/link command
(just like .o files) to be linked into your program without the
need to create library stub files. For more about how to do that,
try
Colin
Peters' DLL Page
(from Colin
Peters' Win32 Programming Page). Colin Peters started MinGW. Also,
regarding function name mangling (decorating) in MinGW, try
Wu YongWei's
Page (local copy here).
No Globbing
By default compile, if you run a MinGW compiled command-line utility and
pass it a wildcard argument such as *.c, it acts exactly as a unix
utility and looks for every file ending in .c in your current file
directory, replacing the *.c argument with the name of every one of
those files so that your program never actually sees the *.c. To prevent
this "globbing," put CRT_noglob.o
(in the MinGW library
directory) at the beginning of your link list when linking.
No Console Window
To make sure your application doesn't open a console window, use
the -mwindows flag when linking.
Binary stdout
If you want the output from the stdout FILE stream to be
binary (no translation of CR/LF chars):
#ifdef __MINGW32__
/* Required header file */
#include <fcntl.h>
#endif
...
#ifdef __MINGW32__
/* Switch to binary mode */
_setmode(_fileno(stdout),_O_BINARY);
#endif
Seeing all predefined macros
Create a file test.c that has one line in it:
int main(void) {}
Then compile with this command:
gcc -dM -E test.c
Even easier (I got an e-mail tip on this)
gcc -dM -E -
(Type in the above, press ENTER, then, in Unix, press CTRL-D, or from the Windows CMD line, press CTRL-Z or F6 followed by the ENTER key.)
(These work with any gcc port.)
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