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Fix formatting real to binary and hex strings on ARM 

Directly casting a negative double to a unsigned integer type is undefined
behavior and has different results on x86 and ARM based platforms.

On x86 the behavior is similar to casting a signed int to an unsigned
integer, i.e. the sign bit will end up in the MSB. But on ARM the result
will be 0.

To get consistent behavior, first cast to signed integer and then cast the
signed integer value to an unsigned integer value.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
This commit is contained in:
Lars-Peter Clausen 2023-05-08 08:09:12 -07:00
parent b210eb8264
commit abe1099335
1 changed files with 11 additions and 3 deletions
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14
vvp/vpi_callback.cc
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@ -858,6 +858,14 @@ static double vlg_round(double rval)
}
}
static uint64_t vlg_round_to_u64(double rval)
{
// Directly casting a negative double to an unsigned integer types is
// undefined behavior and behaves differently on different architectures.
// Cast to signed integer first to get the behavior we want.
return static_cast<uint64_t>(static_cast<int64_t>(vlg_round(rval)));
}
static void real_signal_value(struct t_vpi_value*vp, double rval)
{
static const size_t RBUF_SIZE = 64 + 1;
@ -890,12 +898,12 @@ static void real_signal_value(struct t_vpi_value*vp, double rval)
break;
case vpiHexStrVal:
snprintf(rbuf, RBUF_SIZE, "%" PRIx64, (uint64_t)vlg_round(rval));
snprintf(rbuf, RBUF_SIZE, "%" PRIx64, vlg_round_to_u64(rval));
vp->value.str = rbuf;
break;
case vpiBinStrVal: {
uint64_t val = (uint64_t)vlg_round(rval);
uint64_t val = vlg_round_to_u64(rval);
unsigned len = 0;
while (val > 0) {
@ -903,7 +911,7 @@ static void real_signal_value(struct t_vpi_value*vp, double rval)
val /= 2;
}
val = (uint64_t)vlg_round(rval);
val = vlg_round_to_u64(rval);
for (unsigned idx = 0 ; idx < len ; idx += 1) {
rbuf[len-idx-1] = (val & 1)? '1' : '0';
val /= 2;