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Full Discussion: C multiplication with GCC
Top Forums Programming C multiplication with GCC Post 302544983 by pheonix on Friday 5th of August 2011 03:50:14 PM
Old 08-05-2011
It wasn't about the imul instruction of intel, it was about GCC insisting that my "C" language statement wasn't a 32x32bit multiply just because the constant had the 31st bit set. GCC insisted that it should be done as a 64x32bit multiply. I saw no reason for a 2^17 * 2^32 should be done differently than a 2^17 *( 2^32 >> 1) considering they were unsigned multiplication. No reason to take high 32 of 2^17 = 0 * 2290649225 + low 32 of 2^17 * 2290649225, add in sign adjustment for the 2^17 for the answer. Especially since it doesn't do that on 2^17 * (2^32 >> 1).

I probably really shouldn't care how a compiler interprets a "C" statement. By the use of one "unsigned" where you normally don't need it, I can execute 4 instructions instead of 12 instructions. I never knew that it considered converting to "unsigned long long" was the same as converting to "long long" in this one instance. On a PPC execute 9 instructions instead of 21. And if done ppc asm only 5 (extra mr).
 

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LEARN ABOUT DEBIAN

perldgux

PERLDGUX(1)						 Perl Programmers Reference Guide					       PERLDGUX(1)

NAME

       perldgux - Perl under DG/UX.

SYNOPSIS

       One can read this document in the following formats:

	       man perldgux
	       view perl perldgux
	       explorer perldgux.html
	       info perldgux

       to list some (not all may be available simultaneously), or it may be read as is: as README.dgux.

DESCRIPTION

       Perl 5.7/8.x for DG/UX ix86 R4.20MU0x

BUILDING PERL ON DG
/UX
   Non-threaded Perl on DG/UX
       Just run ./Configure script from the top directory.  Then give "make" to compile.

   Threaded Perl on DG/UX
       If you are using as compiler GCC-2.95.x rev(DG/UX) an easy solution for configuring perl in your DG/UX machine is to run the command:

       ./Configure -Dusethreads -Duseithreads -Dusedevel -des

       This will automatically accept all the defaults and in particular /usr/local/ as installation directory.  Note that GCC-2.95.x rev(DG/UX)
       knows the switch -pthread which allows it to link correctly DG/UX's -lthread library.

       If you want to change the installation directory or have a standard DG/UX with C compiler GCC-2.7.2.x then you have no choice than to do an
       interactive build by issuing the command:

       ./Configure -Dusethreads -Duseithreads

       In particular with GCC-2.7.2.x accept all the defaults and *watch* out for the message:

	   Any additional ld flags (NOT including libraries)? [ -pthread]

       Instead of -pthread put here -lthread. CGCC-2.7.2.x that comes with the DG/UX OS does NOT know the -pthread switch. So your build will fail
       if you choose the defaults.  After configuration is done correctly give "make" to compile.

   Testing Perl on DG/UX
       Issuing a "make test" will run all the tests.  If the test lib/ftmp-security gives you as a result something like

	   lib/ftmp-security....File::Temp::_gettemp:
	   Parent directory (/tmp/) is not safe (sticky bit not set
	   when world writable?) at lib/ftmp-security.t line 100

       don't panic and just set the sticky bit in your /tmp directory by doing the following as root:

       cd / chmod +t /tmp (=set the sticky bit to /tmp).

       Then rerun the tests. This time all must be OK.

   Installing the built perl on DG/UX
       Run the command "make install"

AUTHOR

       Takis Psarogiannakopoulos University of Cambridge Centre for Mathematical Sciences Department of Pure Mathematics Wilberforce road
       Cambridge CB3 0WB , UK email <takis@XFree86.Org>

SEE ALSO

       perl(1).

perl v5.14.2							    2011-09-19							       PERLDGUX(1)
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