Mercurial > hg
changeset 373:67081329d49a
Change the size of the short hash representation
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Hash: SHA1
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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| author | mpm@selenic.com |
|---|---|
| date | Wed, 15 Jun 2005 21:11:40 -0800 |
| parents | 4b0f562c61f4 |
| children | f07d00fcd281 |
| files | mercurial/revlog.py |
| diffstat | 1 files changed, 1 insertions(+), 1 deletions(-) [+] |
line wrap: on
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--- a/mercurial/revlog.py Wed Jun 15 19:58:48 2005 -0800 +++ b/mercurial/revlog.py Wed Jun 15 21:11:40 2005 -0800 @@ -13,7 +13,7 @@ def hex(node): return binascii.hexlify(node) def bin(node): return binascii.unhexlify(node) -def short(node): return hex(node[:4]) +def short(node): return hex(node[:6]) def compress(text): if not text: return text