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timer: fix (usually impossible) timespec.tv_sec overflow 

This usually can't happen, because even if time_us (first input value)
is INT64_MAX, the value added to tv_sec will be about 2^43, and tv_sec
will be <2^31, far below a possible overflow in 64 bits. But should
time_t be 32 bits (32 bit Linux/Windows?), an overflow could happen.
This commit is contained in:
wm4 2014-05-22 20:55:36 +02:00
parent 7b7e15a460
commit d31b594f77
1 changed files with 13 additions and 1 deletions
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14
osdep/timer.c
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@ -90,6 +90,16 @@ static void get_realtime(struct timespec *out_ts)
#endif
}
// Calculate the maximum of type T, assuming it's a signed integer type and
// represented in 2's complement.
// Works like: (1 << 14) + ((1 << 14) - 1) == (1 << 15) - 1 (but no overflow)
#define SIGNED_MAX(T) ((((T)1) << (sizeof(T) * 8 - 2)) + \
((((T)1) << (sizeof(T) * 8 - 2)) - 1))
// If you don't like this, go fix POSIX. tv_sec is time_t, but time_t is
// an unknown integer type, and the limits are unknown to the application.
#define MAX_TIME_T SIGNED_MAX(time_t)
struct timespec mp_time_us_to_timespec(int64_t time_us)
{
struct timespec ts;
@ -98,7 +108,7 @@ struct timespec mp_time_us_to_timespec(int64_t time_us)
// CLOCK_REALTIME - so we have to remap the times.
int64_t unow = mp_time_us();
int64_t diff_us = time_us - unow;
long diff_secs = diff_us / (1000L * 1000L);
int64_t diff_secs = diff_us / (1000L * 1000L);
long diff_nsecs = (diff_us - diff_secs * (1000L * 1000L)) * 1000L;
if (diff_nsecs < 0) {
diff_secs -= 1;
@ -108,6 +118,8 @@ struct timespec mp_time_us_to_timespec(int64_t time_us)
diff_secs += 1;
diff_nsecs -= 1000000000UL;
}
if (diff_secs > MAX_TIME_T - ts.tv_sec)
diff_secs = MAX_TIME_T - ts.tv_sec;
ts.tv_sec += diff_secs;
ts.tv_nsec += diff_nsecs;
return ts;