[Qemu-devel] [PULL 02/12] target/mips: Make the results of MOD_<U|S>.<B|H|W|D> the same as on hardware

[Aleksandar Markovic]

From: Mateja Marjanovic <address@hidden>

MSA instructions MOD_<U|S>.<B|H|W|D> when dividing by zero,
didn't return the same value when executed on a referent hardware
(FPGA MIPS 64 r6, little endian) and when executed on QEMU, which
is not a real bug, because the result when dividing by zero is
UNPREDICTABLE [1] (page 255, 256).

[1] MIPS Architecture for Programmers
    Volume IV-j: The MIPS64 SIMD
    Architecture Module, Revision 1.12

Signed-off-by: Mateja Marjanovic <address@hidden>
Signed-off-by: Aleksandar Markovic <address@hidden>
Reviewed-by: Aleksandar Markovic <address@hidden>
Message-Id: <address@hidden>
---
 target/mips/msa_helper.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/mips/msa_helper.c b/target/mips/msa_helper.c
index 596190b..274c6ca 100644
--- a/target/mips/msa_helper.c
+++ b/target/mips/msa_helper.c
@@ -657,14 +657,14 @@ static inline int64_t msa_mod_s_df(uint32_t df, int64_t 
arg1, int64_t arg2)
     if (arg1 == DF_MIN_INT(df) && arg2 == -1) {
         return 0;
     }
-    return arg2 ? arg1 % arg2 : 0;
+    return arg2 ? arg1 % arg2 : arg1;
 }
 
 static inline int64_t msa_mod_u_df(uint32_t df, int64_t arg1, int64_t arg2)
 {
     uint64_t u_arg1 = UNSIGNED(arg1, df);
     uint64_t u_arg2 = UNSIGNED(arg2, df);
-    return u_arg2 ? u_arg1 % u_arg2 : 0;
+    return u_arg2 ? u_arg1 % u_arg2 : u_arg1;
 }
 
 #define SIGNED_EVEN(a, df) \
-- 
2.7.4