--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/lib-old/cmpcache.py	Thu Feb 03 15:26:16 2000 +0000
@@ -0,0 +1,64 @@
+"""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