upstream/mercurial-mirror Files · mercurial/pure/diffhelpers.py

revlog: make compressed size comparisons consistent...

revlog: make compressed size comparisons consistent revlog.compress() compares the compressed size to the input size and throws away the compressed data if it is larger than the input. This is the correct thing to do, as storing compressed data that is larger than the input takes up more storage space and makes reading slower. However, the comparison was implemented inconsistently. For the streaming compression mode, we threw away the result if it was greater than or equal to the input size. But for the one-shot compression, we threw away the compression only if it was greater than the input size! This patch changes the comparison for the simple case so it is consistent with the streaming case. As a few tests demonstrate, this adds 1 byte to some revlog entries. This is because of an added 'u' header on the chunk. It seems somewhat wrong to increase the revlog size here. However, IMO the cost of 1 byte in storage is insignificant compared to the performance gains of avoiding decompression. This patch should invite questions around the heuristic for throwing away compressed data. For example, I'd argue we should be more liberal about rejecting compressed data, additionally doing so where the number of bytes saved fails to reach a threshold. But we can have this discussion another time.

Gregory Szorc - - Load All Authors

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      # diffhelpers.py - pure Python implementation of diffhelpers.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 or any later version.

      from __future__ import absolute_import

      def addlines(fp, hunk, lena, lenb, a, b):

          while True:

              todoa = lena - len(a)

              todob = lenb - len(b)

              num = max(todoa, todob)

              if num == 0:

                  break

              for i in xrange(num):

                  s = fp.readline()

                  c = s[0]

                  if s == "\\ No newline at end of file\n":

                      fix_newline(hunk, a, b)

                      continue

                  if c == "\n":

                      # Some patches may be missing the control char

                      # on empty lines. Supply a leading space.

                      s = " \n"

                  hunk.append(s)

                  if c == "+":

                      b.append(s[1:])

                  elif c == "-":

                      a.append(s)

                  else:

                      b.append(s[1:])

                      a.append(s)

          return 0

      def fix_newline(hunk, a, b):

          l = hunk[-1]

          # tolerate CRLF in last line

          if l.endswith('\r\n'):

              hline = l[:-2]

          else:

              hline = l[:-1]

          c = hline[0]

          if c in " +":

              b[-1] = hline[1:]

          if c in " -":

              a[-1] = hline

          hunk[-1] = hline

          return 0

      def testhunk(a, b, bstart):

          alen = len(a)

          blen = len(b)

          if alen > blen - bstart:

              return -1

          for i in xrange(alen):

              if a[i][1:] != b[i + bstart]:

                  return -1

          return 0

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				# diffhelpers.py - pure Python implementation of diffhelpers.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 or any later version.

				from __future__ import absolute_import

				def addlines(fp, hunk, lena, lenb, a, b):
				while True:
				todoa = lena - len(a)
				todob = lenb - len(b)
				num = max(todoa, todob)
				if num == 0:
				break
				for i in xrange(num):
				s = fp.readline()
				c = s[0]
				if s == "\\ No newline at end of file\n":
				fix_newline(hunk, a, b)
				continue
				if c == "\n":
				# Some patches may be missing the control char
				# on empty lines. Supply a leading space.
				s = " \n"
				hunk.append(s)
				if c == "+":
				b.append(s[1:])
				elif c == "-":
				a.append(s)
				else:
				b.append(s[1:])
				a.append(s)
				return 0

				def fix_newline(hunk, a, b):
				l = hunk[-1]
				# tolerate CRLF in last line
				if l.endswith('\r\n'):
				hline = l[:-2]
				else:
				hline = l[:-1]
				c = hline[0]

				if c in " +":
				b[-1] = hline[1:]
				if c in " -":
				a[-1] = hline
				hunk[-1] = hline
				return 0


				def testhunk(a, b, bstart):
				alen = len(a)
				blen = len(b)
				if alen > blen - bstart:
				return -1
				for i in xrange(alen):
				if a[i][1:] != b[i + bstart]:
				return -1
				return 0