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[174.21.75.75]) by smtp.gmail.com with ESMTPSA id i11sm4120257pgp.18.2021.10.28.21.33.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Oct 2021 21:33:32 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Subject: [PULL v2 02/60] host-utils: move checks out of divu128/divs128 Date: Thu, 28 Oct 2021 21:32:31 -0700 Message-Id: <20211029043329.1518029-3-richard.henderson@linaro.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211029043329.1518029-1-richard.henderson@linaro.org> References: <20211029043329.1518029-1-richard.henderson@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2607:f8b0:4864:20::62c; envelope-from=richard.henderson@linaro.org; helo=mail-pl1-x62c.google.com 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: Luis Pires Errors-To: qemu-devel-bounces+patch=linaro.org@nongnu.org Sender: "Qemu-devel" From: Luis Pires In preparation for changing the divu128/divs128 implementations to allow for quotients larger than 64 bits, move the div-by-zero and overflow checks to the callers. Signed-off-by: Luis Pires Reviewed-by: Richard Henderson Message-Id: <20211025191154.350831-2-luis.pires@eldorado.org.br> Signed-off-by: Richard Henderson --- include/hw/clock.h | 5 +++-- include/qemu/host-utils.h | 34 ++++++++++++--------------------- target/ppc/int_helper.c | 14 +++++++++----- util/host-utils.c | 40 ++++++++++++++++++--------------------- 4 files changed, 42 insertions(+), 51 deletions(-) -- 2.25.1 diff --git a/include/hw/clock.h b/include/hw/clock.h index 11f67fb970..7443e6c4ab 100644 --- a/include/hw/clock.h +++ b/include/hw/clock.h @@ -324,8 +324,9 @@ static inline uint64_t clock_ns_to_ticks(const Clock *clk, uint64_t ns) return 0; } /* - * Ignore divu128() return value as we've caught div-by-zero and don't - * need different behaviour for overflow. + * BUG: when CONFIG_INT128 is not defined, the current implementation of + * divu128 does not return a valid truncated quotient, so the result will + * be wrong. */ divu128(&lo, &hi, clk->period); return lo; diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h index ca9f3f021b..e82e6239af 100644 --- a/include/qemu/host-utils.h +++ b/include/qemu/host-utils.h @@ -52,36 +52,26 @@ static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c) return (__int128_t)a * b / c; } -static inline int divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor) +static inline void divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor) { - if (divisor == 0) { - return 1; - } else { - __uint128_t dividend = ((__uint128_t)*phigh << 64) | *plow; - __uint128_t result = dividend / divisor; - *plow = result; - *phigh = dividend % divisor; - return result > UINT64_MAX; - } + __uint128_t dividend = ((__uint128_t)*phigh << 64) | *plow; + __uint128_t result = dividend / divisor; + *plow = result; + *phigh = dividend % divisor; } -static inline int divs128(int64_t *plow, int64_t *phigh, int64_t divisor) +static inline void divs128(int64_t *plow, int64_t *phigh, int64_t divisor) { - if (divisor == 0) { - return 1; - } else { - __int128_t dividend = ((__int128_t)*phigh << 64) | (uint64_t)*plow; - __int128_t result = dividend / divisor; - *plow = result; - *phigh = dividend % divisor; - return result != *plow; - } + __int128_t dividend = ((__int128_t)*phigh << 64) | (uint64_t)*plow; + __int128_t result = dividend / divisor; + *plow = result; + *phigh = dividend % divisor; } #else void muls64(uint64_t *plow, uint64_t *phigh, int64_t a, int64_t b); void mulu64(uint64_t *plow, uint64_t *phigh, uint64_t a, uint64_t b); -int divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor); -int divs128(int64_t *plow, int64_t *phigh, int64_t divisor); +void divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor); +void divs128(int64_t *plow, int64_t *phigh, int64_t divisor); static inline uint64_t muldiv64(uint64_t a, uint32_t b, uint32_t c) { diff --git a/target/ppc/int_helper.c b/target/ppc/int_helper.c index f5dac3aa87..510faf24cf 100644 --- a/target/ppc/int_helper.c +++ b/target/ppc/int_helper.c @@ -104,10 +104,11 @@ uint64_t helper_divdeu(CPUPPCState *env, uint64_t ra, uint64_t rb, uint32_t oe) uint64_t rt = 0; int overflow = 0; - overflow = divu128(&rt, &ra, rb); - - if (unlikely(overflow)) { + if (unlikely(rb == 0 || ra >= rb)) { + overflow = 1; rt = 0; /* Undefined */ + } else { + divu128(&rt, &ra, rb); } if (oe) { @@ -122,10 +123,13 @@ uint64_t helper_divde(CPUPPCState *env, uint64_t rau, uint64_t rbu, uint32_t oe) int64_t rt = 0; int64_t ra = (int64_t)rau; int64_t rb = (int64_t)rbu; - int overflow = divs128(&rt, &ra, rb); + int overflow = 0; - if (unlikely(overflow)) { + if (unlikely(rb == 0 || uabs64(ra) >= uabs64(rb))) { + overflow = 1; rt = 0; /* Undefined */ + } else { + divs128(&rt, &ra, rb); } if (oe) { diff --git a/util/host-utils.c b/util/host-utils.c index a789a11b46..701a371843 100644 --- a/util/host-utils.c +++ b/util/host-utils.c @@ -86,24 +86,23 @@ void muls64 (uint64_t *plow, uint64_t *phigh, int64_t a, int64_t b) *phigh = rh; } -/* Unsigned 128x64 division. Returns 1 if overflow (divide by zero or */ -/* quotient exceeds 64 bits). Otherwise returns quotient via plow and */ -/* remainder via phigh. */ -int divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor) +/* + * Unsigned 128-by-64 division. Returns quotient via plow and + * remainder via phigh. + * The result must fit in 64 bits (plow) - otherwise, the result + * is undefined. + * This function will cause a division by zero if passed a zero divisor. + */ +void divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor) { uint64_t dhi = *phigh; uint64_t dlo = *plow; unsigned i; uint64_t carry = 0; - if (divisor == 0) { - return 1; - } else if (dhi == 0) { + if (divisor == 0 || dhi == 0) { *plow = dlo / divisor; *phigh = dlo % divisor; - return 0; - } else if (dhi >= divisor) { - return 1; } else { for (i = 0; i < 64; i++) { @@ -120,15 +119,20 @@ int divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor) *plow = dlo; *phigh = dhi; - return 0; } } -int divs128(int64_t *plow, int64_t *phigh, int64_t divisor) +/* + * Signed 128-by-64 division. Returns quotient via plow and + * remainder via phigh. + * The result must fit in 64 bits (plow) - otherwise, the result + * is undefined. + * This function will cause a division by zero if passed a zero divisor. + */ +void divs128(int64_t *plow, int64_t *phigh, int64_t divisor) { int sgn_dvdnd = *phigh < 0; int sgn_divsr = divisor < 0; - int overflow = 0; if (sgn_dvdnd) { *plow = ~(*plow); @@ -145,19 +149,11 @@ int divs128(int64_t *plow, int64_t *phigh, int64_t divisor) divisor = 0 - divisor; } - overflow = divu128((uint64_t *)plow, (uint64_t *)phigh, (uint64_t)divisor); + divu128((uint64_t *)plow, (uint64_t *)phigh, (uint64_t)divisor); if (sgn_dvdnd ^ sgn_divsr) { *plow = 0 - *plow; } - - if (!overflow) { - if ((*plow < 0) ^ (sgn_dvdnd ^ sgn_divsr)) { - overflow = 1; - } - } - - return overflow; } #endif