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Re: [Qemu-devel] [PATCH] target-ppc: fix nego and subf*o instructions


From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH] target-ppc: fix nego and subf*o instructions
Date: Sun, 31 Mar 2013 16:19:45 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4

On 2013-03-30 16:54, Aurelien Jarno wrote:
The overflow computation of nego and subf*o instructions has been broken
in commit ffe30937. This patch fixes it.

With this change the PPC emulation passes the Gwenole Beauchesne
testsuite again.

Cc: Alexander Graf <address@hidden>
Cc: Richard Henderson <address@hidden>
Signed-off-by: Aurelien Jarno <address@hidden>
---
  target-ppc/translate.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target-ppc/translate.c b/target-ppc/translate.c
index 5e741d1..062493a 100644
--- a/target-ppc/translate.c
+++ b/target-ppc/translate.c
@@ -749,7 +749,7 @@ static inline void gen_op_arith_compute_ov(DisasContext 
*ctx, TCGv arg0,
      tcg_gen_xor_tl(cpu_ov, arg0, arg1);
      tcg_gen_xor_tl(t0, arg1, arg2);
      if (sub) {
-        tcg_gen_and_tl(cpu_ov, cpu_ov, t0);
+        tcg_gen_andc_tl(cpu_ov, t0, cpu_ov);
      } else {
          tcg_gen_andc_tl(cpu_ov, cpu_ov, t0);
      }

I'm a bit confused. This is the exact same algorithm that's used on ARM and i386. And as far as I can determine, all three platforms have the same definition of "overflow".


r~



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