projects / OpenSPARC-T2-SAM / blame
| Commit | Line | Data |
|---|---|---|
| 920dae64 AT |
1 | """Efficiently compare files, boolean outcome only (equal / not equal). |
| 2 | ||
| 3 | Tricks (used in this order): | |
| 4 | - Use the statcache module to avoid statting files more than once | |
| 5 | - Files with identical type, size & mtime are assumed to be clones | |
| 6 | - Files with different type or size cannot be identical | |
| 7 | - We keep a cache of outcomes of earlier comparisons | |
| 8 | - We don't fork a process to run 'cmp' but read the files ourselves | |
| 9 | """ | |
| 10 | ||
| 11 | import os | |
| 12 | from stat import * | |
| 13 | import statcache | |
| 14 | ||
| 15 | ||
| 16 | # The cache. | |
| 17 | # | |
| 18 | cache = {} | |
| 19 | ||
| 20 | ||
| 21 | def cmp(f1, f2, shallow=1): | |
| 22 | """Compare two files, use the cache if possible. | |
| 23 | May raise os.error if a stat or open of either fails. | |
| 24 | Return 1 for identical files, 0 for different. | |
| 25 | Raise exceptions if either file could not be statted, read, etc.""" | |
| 26 | s1, s2 = sig(statcache.stat(f1)), sig(statcache.stat(f2)) | |
| 27 | if not S_ISREG(s1[0]) or not S_ISREG(s2[0]): | |
| 28 | # Either is a not a plain file -- always report as different | |
| 29 | return 0 | |
| 30 | if shallow and s1 == s2: | |
| 31 | # type, size & mtime match -- report same | |
| 32 | return 1 | |
| 33 | if s1[:2] != s2[:2]: # Types or sizes differ, don't bother | |
| 34 | # types or sizes differ -- report different | |
| 35 | return 0 | |
| 36 | # same type and size -- look in the cache | |
| 37 | key = f1 + ' ' + f2 | |
| 38 | if cache.has_key(key): | |
| 39 | cs1, cs2, outcome = cache[key] | |
| 40 | # cache hit | |
| 41 | if s1 == cs1 and s2 == cs2: | |
| 42 | # cached signatures match | |
| 43 | return outcome | |
| 44 | # stale cached signature(s) | |
| 45 | # really compare | |
| 46 | outcome = do_cmp(f1, f2) | |
| 47 | cache[key] = s1, s2, outcome | |
| 48 | return outcome | |
| 49 | ||
| 50 | def sig(st): | |
| 51 | """Return signature (i.e., type, size, mtime) from raw stat data.""" | |
| 52 | return S_IFMT(st[ST_MODE]), st[ST_SIZE], st[ST_MTIME] | |
| 53 | ||
| 54 | def do_cmp(f1, f2): | |
| 55 | """Compare two files, really.""" | |
| 56 | #print ' cmp', f1, f2 # XXX remove when debugged | |
| 57 | bufsize = 8*1024 # Could be tuned | |
| 58 | fp1 = open(f1, 'rb') | |
| 59 | fp2 = open(f2, 'rb') | |
| 60 | while 1: | |
| 61 | b1 = fp1.read(bufsize) | |
| 62 | b2 = fp2.read(bufsize) | |
| 63 | if b1 != b2: return 0 | |
| 64 | if not b1: return 1 |