From 59d9413094d7295d74926e63d7df4963399ab53a Mon Sep 17 00:00:00 2001 From: aurel32 Date: Thu, 8 Jan 2009 18:48:12 +0000 Subject: [PATCH] target-mips: CP0 Random register improvements MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit - Use a LFSR to generate the random value - Make sure to not return the same value twice Based on a patch by Hervé Poussineau. Signed-off-by: Aurelien Jarno git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6233 c046a42c-6fe2-441c-8c8c-71466251a162 --- hw/mips_timer.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/hw/mips_timer.c b/hw/mips_timer.c index 13217b2da0..67b873511c 100644 --- a/hw/mips_timer.c +++ b/hw/mips_timer.c @@ -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; }