diff options
| -rw-r--r-- | changes/bug40684 | 6 | ||||
| -rw-r--r-- | src/lib/time/compat_time.c | 11 |
2 files changed, 13 insertions, 4 deletions
diff --git a/changes/bug40684 b/changes/bug40684 new file mode 100644 index 0000000000..8c751ede2c --- /dev/null +++ b/changes/bug40684 @@ -0,0 +1,6 @@ + o Major bugfixes (OSX): + - Fix coarse-time computation on Apple platforms (like Mac M1) where + the Mach absolute time ticks do not correspond directly to + nanoseconds. Previously, we computed our shift value wrong, which + led us to give incorrect timing results. + Fixes bug 40684; bugfix on 0.3.3.1-alpha. diff --git a/src/lib/time/compat_time.c b/src/lib/time/compat_time.c index 6bbad4f98a..9a5ce062d7 100644 --- a/src/lib/time/compat_time.c +++ b/src/lib/time/compat_time.c @@ -253,11 +253,14 @@ monotime_init_internal(void) tor_assert(mach_time_info.denom != 0); { - // approximate only. - uint64_t ns_per_tick = mach_time_info.numer / mach_time_info.denom; - uint64_t ms_per_tick = ns_per_tick * ONE_MILLION; + // We want to compute this, approximately: + // uint64_t ns_per_tick = mach_time_info.numer / mach_time_info.denom; + // uint64_t ticks_per_ms = ONE_MILLION / ns_per_tick; + // This calculation multiplies first, though, to improve accuracy. + uint64_t ticks_per_ms = (ONE_MILLION * mach_time_info.denom) + / mach_time_info.numer; // requires that tor_log2(0) == 0. - monotime_shift = tor_log2(ms_per_tick); + monotime_shift = tor_log2(ticks_per_ms); } { // For converting ticks to milliseconds in a 32-bit-friendly way, we |