Initial commit of OpenSPARC T2 architecture model.

[OpenSPARC-T2-SAM] / sam-t2 / devtools / v9 / lib / python2.4 / lib-old / cmpcache.py

"""Efficiently compare files, boolean outcome only (equal / not equal).

Tricks (used in this order):
   - Use the statcache module to avoid statting files more than once
   - 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
from stat import *
import statcache


# The cache.
#
cache = {}


def cmp(f1, f2, shallow=1):
   """Compare two files, use the cache if possible.
   May raise os.error if a stat or open of either fails.
   Return 1 for identical files, 0 for different.
   Raise exceptions if either file could not be statted, read, etc."""
   s1, s2 = sig(statcache.stat(f1)), sig(statcache.stat(f2))
   if not S_ISREG(s1[0]) or not S_ISREG(s2[0]):
       # 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
   if cache.has_key(key):
       cs1, cs2, outcome = cache[key]
       # cache hit
       if s1 == cs1 and s2 == cs2:
           # cached signatures match
           return outcome
       # stale cached signature(s)
   # 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."""
   return S_IFMT(st[ST_MODE]), st[ST_SIZE], st[ST_MTIME]

def do_cmp(f1, f2):
   """Compare two files, really."""
   #print '    cmp', f1, f2 # XXX remove when debugged
   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