[Qemu-devel] [PATCH v2 1/2] target/mips: Make the results of DIV_<U|S>.<B|H|W|D> the same as on hardware

[Mateja Marjanovic <mateja.marjanovic@rt-rk.com>]

From: Mateja Marjanovic <Mateja.Marjanovic@rt-rk.com>

MSA instructions DIV_<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 141, 142).

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

Signed-off-by: Mateja Marjanovic <mateja.marjanovic@rt-rk.com>
---
 target/mips/msa_helper.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/target/mips/msa_helper.c b/target/mips/msa_helper.c
index 655148d..8c77f12 100644
--- a/target/mips/msa_helper.c
+++ b/target/mips/msa_helper.c
@@ -641,14 +641,15 @@ static inline int64_t msa_div_s_df(uint32_t df, int64_t arg1, int64_t arg2)
     if (arg1 == DF_MIN_INT(df) && arg2 == -1) {
         return DF_MIN_INT(df);
     }
-    return arg2 ? arg1 / arg2 : 0;
+    return arg2 ? arg1 / arg2
+                : arg1 >= 0 ? -1 : 1;
 }
 
 static inline int64_t msa_div_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 arg2 ? u_arg1 / u_arg2 : -1;
 }
 
 static inline int64_t msa_mod_s_df(uint32_t df, int64_t arg1, int64_t arg2)
-- 
2.7.4