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[tor-commits] [tor/maint-0.3.4] Use a slightly more accurate formula for OSX 32-bit msec conversion
commit 4eabc6db47fe64b6757f7a5f0e651a41f02efca3
Author: Nick Mathewson <nickm@xxxxxxxxxxxxxx>
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;
}
}
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