commit 4eabc6db47fe64b6757f7a5f0e651a41f02efca3 Author: Nick Mathewson nickm@torproject.org Date: Fri Sep 14 08:30:24 2018 -0400
Use a slightly more accurate formula for OSX 32-bit msec conversion
We use an optimized but less accurate formula for converting coarse time differences to milliseconds on 32-bit OSX platforms, so that we can avoid 64-bit division.
The old numbers were off by 0.4%. The new numbers are off by .006%.
This should make the unit tests a bit cleaner, and our tolerances a bit closer. --- src/common/compat_time.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/src/common/compat_time.c b/src/common/compat_time.c index 40847a844..f92dc09c4 100644 --- a/src/common/compat_time.c +++ b/src/common/compat_time.c @@ -299,11 +299,11 @@ monotime_init_internal(void) } { // For converting ticks to milliseconds in a 32-bit-friendly way, we - // will first right-shift by 20, and then multiply by 20/19, since - // (1<<20) * 19/20 is about 1e6. We precompute a new numerate and + // will first right-shift by 20, and then multiply by 2048/1953, since + // (1<<20) * 1953/2048 is about 1e6. We precompute a new numerator and // denominator here to avoid multiple multiplies. - mach_time_info_msec_cvt.numer = mach_time_info.numer * 20; - mach_time_info_msec_cvt.denom = mach_time_info.denom * 19; + mach_time_info_msec_cvt.numer = mach_time_info.numer * 2048; + mach_time_info_msec_cvt.denom = mach_time_info.denom * 1953; } }