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gdatetime: Mark the usecs as volatile

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On i386, we were seeing that this calculation was producing an incorrect
result, probably because usec was being stored in an 80-bit register
before being written back into a 64-bit float in memory. If we mark the
variables as volatile, they are not stored in registers and we avoid
this bug.
This commit is contained in:
Iain Lane
2018-01-12 11:24:47 +00:00
parent d870628782
commit e2054240c2
1 changed files with 7 additions and 2 deletions
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9
glib/gdatetime.c
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@@ -1294,7 +1294,11 @@ g_date_time_new (GTimeZone *tz,
{ {
GDateTime *datetime; GDateTime *datetime;
gint64 full_time; gint64 full_time;
gint64 usec; /* keep these variables as volatile. We do not want them ending up in
* registers - them doing so may cause us to hit precision problems on i386.
* See: https://bugzilla.gnome.org/show_bug.cgi?id=792410 */
volatile gint64 usec;
volatile gdouble usecd;
g_return_val_if_fail (tz != NULL, NULL); g_return_val_if_fail (tz != NULL, NULL);
@@ -1328,7 +1332,8 @@ g_date_time_new (GTimeZone *tz,
* FP numbers work. * FP numbers work.
* See https://bugzilla.gnome.org/show_bug.cgi?id=697715. */ * See https://bugzilla.gnome.org/show_bug.cgi?id=697715. */
usec = seconds * USEC_PER_SECOND; usec = seconds * USEC_PER_SECOND;
if ((usec + 1) * 1e-6 <= seconds) { usecd = (usec + 1) * 1e-6;
if (usecd <= seconds) {
usec++; usec++;
} }