| """Efficiently compare files, boolean outcome only (equal / not equal). |
| |
| Tricks (used in this order): |
| - Files with identical type, size & mtime are assumed to be clones |
| - Files with different type or size cannot be identical |
| - We keep a cache of outcomes of earlier comparisons |
| - We don't fork a process to run 'cmp' but read the files ourselves |
| """ |
| |
| import os |
| |
| cache = {} |
| |
| def cmp(f1, f2, shallow=1): |
| """Compare two files, use the cache if possible. |
| Return 1 for identical files, 0 for different. |
| Raise exceptions if either file could not be statted, read, etc.""" |
| s1, s2 = sig(os.stat(f1)), sig(os.stat(f2)) |
| if s1[0] != 8 or s2[0] != 8: |
| # Either is a not a plain file -- always report as different |
| return 0 |
| if shallow and s1 == s2: |
| # type, size & mtime match -- report same |
| return 1 |
| if s1[:2] != s2[:2]: # Types or sizes differ, don't bother |
| # types or sizes differ -- report different |
| return 0 |
| # same type and size -- look in the cache |
| key = (f1, f2) |
| try: |
| cs1, cs2, outcome = cache[key] |
| # cache hit |
| if s1 == cs1 and s2 == cs2: |
| # cached signatures match |
| return outcome |
| # stale cached signature(s) |
| except KeyError: |
| # cache miss |
| pass |
| # really compare |
| outcome = do_cmp(f1, f2) |
| cache[key] = s1, s2, outcome |
| return outcome |
| |
| def sig(st): |
| """Return signature (i.e., type, size, mtime) from raw stat data |
| 0-5: st_mode, st_ino, st_dev, st_nlink, st_uid, st_gid |
| 6-9: st_size, st_atime, st_mtime, st_ctime""" |
| type = st[0] / 4096 |
| size = st[6] |
| mtime = st[8] |
| return type, size, mtime |
| |
| def do_cmp(f1, f2): |
| """Compare two files, really.""" |
| bufsize = 8*1024 # Could be tuned |
| fp1 = open(f1, 'rb') |
| fp2 = open(f2, 'rb') |
| while 1: |
| b1 = fp1.read(bufsize) |
| b2 = fp2.read(bufsize) |
| if b1 != b2: return 0 |
| if not b1: return 1 |