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[216.160.65.90]) by smtp.gmail.com with ESMTPSA id 66sm4746432pfa.92.2020.07.23.20.59.33 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jul 2020 20:59:33 -0700 (PDT) Subject: Re: [PATCH v2 4/7] target/riscv: Check nanboxed inputs to fp helpers To: LIU Zhiwei , qemu-devel@nongnu.org References: <20200724002807.441147-1-richard.henderson@linaro.org> <20200724002807.441147-5-richard.henderson@linaro.org> From: Richard Henderson Message-ID: Date: Thu, 23 Jul 2020 20:59:31 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::641; envelope-from=richard.henderson@linaro.org; helo=mail-pl1-x641.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: frank.chang@sifive.com, alistair23@gmail.com, qemu-riscv@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/23/20 7:47 PM, LIU Zhiwei wrote: > > > On 2020/7/24 8:28, Richard Henderson wrote: >> If a 32-bit input is not properly nanboxed, then the input is >> replaced with the default qnan. >> >> Signed-off-by: Richard Henderson >> --- >>   target/riscv/internals.h  | 11 +++++++ >>   target/riscv/fpu_helper.c | 64 ++++++++++++++++++++++++++++----------- >>   2 files changed, 57 insertions(+), 18 deletions(-) >> >> diff --git a/target/riscv/internals.h b/target/riscv/internals.h >> index 9f4ba7d617..f1a546dba6 100644 >> --- a/target/riscv/internals.h >> +++ b/target/riscv/internals.h >> @@ -43,4 +43,15 @@ static inline uint64_t nanbox_s(float32 f) >>       return f | MAKE_64BIT_MASK(32, 32); >>   } >>   +static inline float32 check_nanbox_s(uint64_t f) >> +{ >> +    uint64_t mask = MAKE_64BIT_MASK(32, 32); >> + >> +    if (likely((f & mask) == mask)) { >> +        return (uint32_t)f; >> +    } else { >> +        return 0x7fc00000u; /* default qnan */ >> +    } >> +} >> + > If possible, > > +static inline float32 check_nanbox(uint64_t f, uint32_t flen) > +{ > +    uint64_t mask = MAKE_64BIT_MASK(flen, 64 - flen); > + > +    if (likely((f & mask) == mask)) { > +        return (uint32_t)f; > +    } else { > +        return (flen == 32) ? 0x7fc00000u : 0x7e00u; /* default qnan */ > +    } > +} The difficulty of choosing the proper default qnan is an example of why we should *not* attempt to make this function fully general, but should instead define separate functions for each type. E.g. static inline float16 check_nanbox_h(uint64_t f); static inline bfloat16 check_nanbox_b(uint64_t f); r~