From: Aurelien Jarno <aurelien@aurel32.net>
To: qemu-devel@nongnu.org
Subject: [Qemu-devel] [6233] target-mips: CP0 Random register improvements
Date: Thu, 08 Jan 2009 18:48:12 +0000 [thread overview]
Message-ID: <E1LKzvQ-0004C4-OO@cvs.savannah.gnu.org> (raw)
Revision: 6233
http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=6233
Author: aurel32
Date: 2009-01-08 18:48:12 +0000 (Thu, 08 Jan 2009)
Log Message:
-----------
target-mips: CP0 Random register improvements
- Use a LFSR to generate the random value
- Make sure to not return the same value twice
Based on a patch by Herv?\195?\169 Poussineau.
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Modified Paths:
--------------
trunk/hw/mips_timer.c
Modified: trunk/hw/mips_timer.c
===================================================================
--- trunk/hw/mips_timer.c 2009-01-08 16:01:33 UTC (rev 6232)
+++ trunk/hw/mips_timer.c 2009-01-08 18:48:12 UTC (rev 6233)
@@ -7,10 +7,15 @@
/* XXX: do not use a global */
uint32_t cpu_mips_get_random (CPUState *env)
{
- static uint32_t seed = 0;
+ static uint32_t lfsr = 1;
+ static uint32_t prev_idx = 0;
uint32_t idx;
- seed = seed * 314159 + 1;
- idx = (seed >> 16) % (env->tlb->nb_tlb - env->CP0_Wired) + env->CP0_Wired;
+ /* Don't return same value twice, so get another value */
+ do {
+ lfsr = (lfsr >> 1) ^ (-(lfsr & 1u) & 0xd0000001u);
+ idx = lfsr % (env->tlb->nb_tlb - env->CP0_Wired) + env->CP0_Wired;
+ } while (idx == prev_idx);
+ prev_idx = idx;
return idx;
}
reply other threads:[~2009-01-08 18:48 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=E1LKzvQ-0004C4-OO@cvs.savannah.gnu.org \
--to=aurelien@aurel32.net \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).