Re: [Qemu-devel] [PATCH v2] target-mips: Fix incorrect shift for SHILO and SHILOV

[Aurelien Jarno <aurelien@aurel32.net>]

On Wed, Dec 05, 2012 at 12:29:10AM +0100, Petar Jovanovic wrote:
> From: Petar Jovanovic <petarj@mips.com>
> 
> helper_shilo has not been shifting an accumulator value correctly for negative
> values in 'shift' field. Minor optimization for shift=0 case.
> This change also adds tests that will trigger issue and check for regressions.
> 
> Signed-off-by: Petar Jovanovic <petarj@mips.com>
> ---
>  target-mips/dsp_helper.c           |   17 +++++++++--------
>  tests/tcg/mips/mips32-dsp/shilo.c  |   18 ++++++++++++++++++
>  tests/tcg/mips/mips32-dsp/shilov.c |   20 ++++++++++++++++++++
>  3 files changed, 47 insertions(+), 8 deletions(-)
> 
> diff --git a/target-mips/dsp_helper.c b/target-mips/dsp_helper.c
> index e7949c2..44f6dc7 100644
> --- a/target-mips/dsp_helper.c
> +++ b/target-mips/dsp_helper.c
> @@ -3814,17 +3814,18 @@ void helper_shilo(target_ulong ac, target_ulong rs, CPUMIPSState *env)
>  
>      rs5_0 = rs & 0x3F;
>      rs5_0 = (int8_t)(rs5_0 << 2) >> 2;
> -    rs5_0 = MIPSDSP_ABS(rs5_0);
> +
> +    if (unlikely(rs5_0 == 0)) {
> +        return;
> +    }
> +
>      acc   = (((uint64_t)env->active_tc.HI[ac] << 32) & MIPSDSP_LHI) |
>              ((uint64_t)env->active_tc.LO[ac] & MIPSDSP_LLO);
> -    if (rs5_0 == 0) {
> -        temp = acc;
> +
> +    if (rs5_0 > 0) {
> +        temp = acc >> rs5_0;
>      } else {
> -        if (rs5_0 > 0) {
> -            temp = acc >> rs5_0;
> -        } else {
> -            temp = acc << rs5_0;
> -        }
> +        temp = acc << -rs5_0;
>      }
>  
>      env->active_tc.HI[ac] = (target_ulong)(int32_t)((temp & MIPSDSP_LHI) >> 32);
> diff --git a/tests/tcg/mips/mips32-dsp/shilo.c b/tests/tcg/mips/mips32-dsp/shilo.c
> index b686616..ce8ebc6 100644
> --- a/tests/tcg/mips/mips32-dsp/shilo.c
> +++ b/tests/tcg/mips/mips32-dsp/shilo.c
> @@ -23,5 +23,23 @@ int main()
>      assert(ach == resulth);
>      assert(acl == resultl);
>  
> +
> +    ach = 0x1;
> +    acl = 0x80000000;
> +
> +    resulth = 0x3;
> +    resultl = 0x0;
> +
> +    __asm
> +        ("mthi %0, $ac1\n\t"
> +         "mtlo %1, $ac1\n\t"
> +         "shilo $ac1, -1\n\t"
> +         "mfhi %0, $ac1\n\t"
> +         "mflo %1, $ac1\n\t"
> +         : "+r"(ach), "+r"(acl)
> +        );
> +    assert(ach == resulth);
> +    assert(acl == resultl);
> +
>      return 0;
>  }
> diff --git a/tests/tcg/mips/mips32-dsp/shilov.c b/tests/tcg/mips/mips32-dsp/shilov.c
> index f186032..e1d6cea 100644
> --- a/tests/tcg/mips/mips32-dsp/shilov.c
> +++ b/tests/tcg/mips/mips32-dsp/shilov.c
> @@ -25,5 +25,25 @@ int main()
>      assert(ach == resulth);
>      assert(acl == resultl);
>  
> +
> +    rs  = 0xffffffff;
> +    ach = 0x1;
> +    acl = 0x80000000;
> +
> +    resulth = 0x3;
> +    resultl = 0x0;
> +
> +    __asm
> +        ("mthi %0, $ac1\n\t"
> +         "mtlo %1, $ac1\n\t"
> +         "shilov $ac1, %2\n\t"
> +         "mfhi %0, $ac1\n\t"
> +         "mflo %1, $ac1\n\t"
> +         : "+r"(ach), "+r"(acl)
> +         : "r"(rs)
> +        );
> +    assert(ach == resulth);
> +    assert(acl == resultl);
> +
>      return 0;
>  }

Thanks, applied. I added a CC: to qemu-stable@nongnu.org, as it is
definitely stable material.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net