Message ID | 20210910112624.72748-6-luis.pires@eldorado.org.br |
---|---|
State | New |
Headers | show |
Series | target/ppc: DFP instructions using decodetree | expand |
On 9/10/21 4:26 AM, Luis Pires wrote: > 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 <luis.pires@eldorado.org.br> Reviewed-by: Richard Henderson <richard.henderson@linaro.org> Frederic, I had forgotten about this work that Luis has done here and in the next 3 patches. This overlaps with what you were doing in the RV128 patch set wrt getting a proper 128-bit divide. r~ > --- > include/hw/clock.h | 5 +++-- > include/qemu/host-utils.h | 36 +++++++++++++---------------------- > target/ppc/int_helper.c | 14 +++++++++----- > util/host-utils.c | 40 ++++++++++++++++++--------------------- > 4 files changed, 43 insertions(+), 52 deletions(-) > > diff --git a/include/hw/clock.h b/include/hw/clock.h > index a7187eab95..5a40a076aa 100644 > --- a/include/hw/clock.h > +++ b/include/hw/clock.h > @@ -320,8 +320,9 @@ 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) > -{ > - 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; > - } > +static inline void divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor) > +{ > + __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 > >
diff --git a/include/hw/clock.h b/include/hw/clock.h index a7187eab95..5a40a076aa 100644 --- a/include/hw/clock.h +++ b/include/hw/clock.h @@ -320,8 +320,9 @@ 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) -{ - 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; - } +static inline void divu128(uint64_t *plow, uint64_t *phigh, uint64_t divisor) +{ + __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
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 <luis.pires@eldorado.org.br> --- include/hw/clock.h | 5 +++-- include/qemu/host-utils.h | 36 +++++++++++++---------------------- target/ppc/int_helper.c | 14 +++++++++----- util/host-utils.c | 40 ++++++++++++++++++--------------------- 4 files changed, 43 insertions(+), 52 deletions(-)