--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Lib/lib-old/cmp.py	Thu Feb 03 15:26:16 2000 +0000
@@ -0,0 +1,63 @@
+"""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