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host-utils: move checks out of divu128/divs128

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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>
Message-Id: <20211025191154.350831-2-luis.pires@eldorado.org.br>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Luis Pires 2021-10-25 16:11:36 -03:00 committed by Richard Henderson
parent 1c46937358
commit 9276a31c34
4 changed files with 42 additions and 51 deletions
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5
include/hw/clock.h
View file

@ -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;

34
include/qemu/host-utils.h
View file

@ -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)
{

14
target/ppc/int_helper.c
View file

@ -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) {

40
util/host-utils.c
View file

@ -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