- 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 <aurelien@aurel32.net>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6233
c046a42c-6fe2-441c-8c8c-
71466251a162
/* 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;
}