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From: | Pádraig Brady |
Subject: | bug#12350: Composites identified as primes in factor.c (when HAVE_GMP) |
Date: | Mon, 08 Oct 2012 15:43:41 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 |
On 10/08/2012 02:21 PM, Torbjorn Granlund wrote:
Jim Meyering <address@hidden> writes: However, this little command does a lot of I/O, too: 191M input, 77M output. Sure. I've never seen significant variance for such stuff, measurable as CPU time. I tested with a Sandybridge i3-2120T now. The range takes 32 s. In both cases, the systems run GNU/Linux. The kernel version is 3.2. The factoring speed varies very much with GCC version. I particular the trial division code has a very tight loop, and such loops have more compiler reliance. GCC 4.6 an later generate code that executes 4 insns per (unsuccessful) division.
gcc (GCC) 4.6.0 20110603 (Red Hat 4.6.0-10) With -march=native -O2
It is also important to use a 32bit binary. We should perhaps have
s/to use/to not use/ I presume. Yep I'm on 64 bit.
provided better 32-bit code paths to be used for numbers < 2^32 on 32-bit hardware. Now, Pádraig's example needs about 3x more time for a 32-bit binary on the same hardware.
thanks, Pádraig.
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