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[Qemu-devel] [6233] target-mips: CP0 Random register improvements
From: |
Aurelien Jarno |
Subject: |
[Qemu-devel] [6233] target-mips: CP0 Random register improvements |
Date: |
Thu, 08 Jan 2009 18:48:12 +0000 |
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 <address@hidden>
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;
}
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