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target/mips: Make the results of DIV_<U|S>.<B|H|W|D> the same as on hardware

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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

Backports commit d2a40a5f6938f30f44b536e997e1e89bb62b971c from qemu
This commit is contained in:
Mateja Marjanovic 2019-05-28 19:24:16 -04:00 committed by Lioncash
parent 1d6acaa604
commit d712d3f226
No known key found for this signature in database
GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 3 additions and 2 deletions
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5
qemu/target/mips/msa_helper.c
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@ -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)