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# mpatch.py - Python implementation of mpatch.c
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#
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# Copyright 2009 Matt Mackall <mpm@selenic.com> and others
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#
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# This software may be used and distributed according to the terms of the
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# GNU General Public License version 2 or any later version.
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import struct
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try:
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from cStringIO import StringIO
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except ImportError:
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from StringIO import StringIO
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# This attempts to apply a series of patches in time proportional to
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# the total size of the patches, rather than patches * len(text). This
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# means rather than shuffling strings around, we shuffle around
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# pointers to fragments with fragment lists.
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#
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# When the fragment lists get too long, we collapse them. To do this
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# efficiently, we do all our operations inside a buffer created by
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# mmap and simply use memmove. This avoids creating a bunch of large
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# temporary string buffers.
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def patches(a, bins):
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if not bins:
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return a
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plens = [len(x) for x in bins]
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pl = sum(plens)
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bl = len(a) + pl
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tl = bl + bl + pl # enough for the patches and two working texts
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b1, b2 = 0, bl
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if not tl:
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return a
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m = StringIO()
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def move(dest, src, count):
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"""move count bytes from src to dest
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The file pointer is left at the end of dest.
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"""
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m.seek(src)
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buf = m.read(count)
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m.seek(dest)
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m.write(buf)
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# load our original text
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m.write(a)
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frags = [(len(a), b1)]
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# copy all the patches into our segment so we can memmove from them
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pos = b2 + bl
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m.seek(pos)
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for p in bins: m.write(p)
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def pull(dst, src, l): # pull l bytes from src
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while l:
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f = src.pop(0)
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if f[0] > l: # do we need to split?
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src.insert(0, (f[0] - l, f[1] + l))
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dst.append((l, f[1]))
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return
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dst.append(f)
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l -= f[0]
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def collect(buf, list):
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start = buf
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for l, p in list:
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move(buf, p, l)
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buf += l
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return (buf - start, start)
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for plen in plens:
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# if our list gets too long, execute it
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if len(frags) > 128:
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b2, b1 = b1, b2
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frags = [collect(b1, frags)]
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new = []
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end = pos + plen
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last = 0
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while pos < end:
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m.seek(pos)
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p1, p2, l = struct.unpack(">lll", m.read(12))
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pull(new, frags, p1 - last) # what didn't change
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pull([], frags, p2 - p1) # what got deleted
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new.append((l, pos + 12)) # what got added
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pos += l + 12
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last = p2
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frags = new + frags # what was left at the end
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t = collect(b2, frags)
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m.seek(t[1])
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return m.read(t[0])
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def patchedsize(orig, delta):
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outlen, last, bin = 0, 0, 0
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binend = len(delta)
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data = 12
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while data <= binend:
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decode = delta[bin:bin + 12]
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start, end, length = struct.unpack(">lll", decode)
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if start > end:
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break
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bin = data + length
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data = bin + 12
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outlen += start - last
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last = end
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outlen += length
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if bin != binend:
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raise ValueError("patch cannot be decoded")
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outlen += orig - last
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return outlen
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