old_contents: # Module 'cmp'
  
  # 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): # 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 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, 'r')
  	fp2 = open(f2, 'r')
  	while 1:
  		b1 = fp1.read(bufsize)
  		b2 = fp2.read(bufsize)
  		if b1 <> b2: return 0
  		if not b1: return 1
  
new_contents: # Module 'cmp'
  
  # 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
  
subject: Patch by Mikael Lyngvig: