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