Initial commit of OpenSPARC T2 architecture model.

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

"""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