Change the size of the short hash representation
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Change the size of the short hash representation
First note that this number doesn't really matter, as we always check
for ambiguous short hash ids.
Here's the math on collision probability:
>>> import math
>>> def p(f, n): return 1 - (1 / math.exp(n**2/(2*f)))
...
>>> p(2**32, 30000.0)
0.09947179164613551 # with 30000 changesets (BKCVS), we have a 9% chance
>>> p(2**32, 65000.0)
0.38850881217977273 # and with a full import from BK, we'd have a 39% chance
>>> p(2**40, 1e6)
0.36539171908447321 # we'd like to be "safe" for 1M csets, so 40 isn't enough
>>> p(2**48, 1e6)
0.001774780051374103 # But 48 looks good
>>> p(2**48, 1e7)
0.16275260939624481
>>> p(2**48, 5e6)
0.043437281083569146
>>> p(2**48, 2e6)
0.0070802434913129764
>>> p(2**48, 3e6)
0.01586009440574343
manifest hash: 24d9f928a463f46708b0e11fb781d5a241851424
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#!/bin/bash
set -e
tests=0
failed=0
H=$PWD
function run_one
{
D=`mktemp -d`
if [ "$D" == "" ] ; then
echo mktemp failed!
fi
cd $D
fail=0
if ! $H/$f > .out 2>&1 ; then
echo $f failed with error code $?
fail=1
fi
if [ -s .out -a ! -r $H/$f.out ] ; then
echo $f generated unexpected output:
cat .out
cp .out $H/$f.err
fail=1
elif [ -r $H/$f.out ] && ! diff -u $H/$f.out .out > /dev/null ; then
echo $f output changed:
diff -u $H/$f.out .out && true
cp .out $H/$f.err
fail=1
fi
cd $H
rm -r $D
return $fail
}
TESTS=$@
if [ "$TESTS" == "" ] ; then
TESTS=`ls test-* | grep -Ev "\.|~"`
fi
for f in $TESTS ; do
echo -n "."
if ! run_one $f ; then
failed=$[$failed + 1]
fi
tests=$[$tests + 1]
done
echo
echo Ran $tests tests, $failed failed
if [ $failed -gt 0 ] ; then
exit 1
fi