bdiff: don't check border condition in loop
This is pretty much a copy of d500ddae7494, just to a different loop.
The condition `p == plast` (`plast == a + len - 1`) was only true on
the final iteration of the loop. So it was wasteful to check for it
on every iteration. We decrease the iteration count by 1 and add an
explicit check for `p == plast` after the loop.
Again, we see modest wins.
From the mozilla-unified repository:
$ perfbdiff -m 3041e4d59df2
! wall 0.035502 comb 0.040000 user 0.040000 sys 0.000000 (best of 100)
! wall 0.030480 comb 0.030000 user 0.030000 sys 0.000000 (best of 100)
$ perfbdiff 0e9928989e9c --alldata --count 100
! wall 4.097394 comb 4.100000 user 4.100000 sys 0.000000 (best of 3)
! wall 3.597798 comb 3.600000 user 3.600000 sys 0.000000 (best of 3)
The 2nd example throws a total of ~3.3GB of data at bdiff. This
change increases the throughput from ~811 MB/s to ~924 MB/s.
#!/usr/bin/env python
#
# Dumps output generated by Mercurial's command server in a formatted style to a
# given file or stderr if '-' is specified. Output is also written in its raw
# format to stdout.
#
# $ ./hg serve --cmds pipe | ./contrib/debugcmdserver.py -
# o, 52 -> 'capabilities: getencoding runcommand\nencoding: UTF-8'
from __future__ import absolute_import, print_function
import struct
import sys
if len(sys.argv) != 2:
print('usage: debugcmdserver.py FILE')
sys.exit(1)
outputfmt = '>cI'
outputfmtsize = struct.calcsize(outputfmt)
if sys.argv[1] == '-':
log = sys.stderr
else:
log = open(sys.argv[1], 'a')
def read(size):
data = sys.stdin.read(size)
if not data:
raise EOFError
sys.stdout.write(data)
sys.stdout.flush()
return data
try:
while True:
header = read(outputfmtsize)
channel, length = struct.unpack(outputfmt, header)
log.write('%s, %-4d' % (channel, length))
if channel in 'IL':
log.write(' -> waiting for input\n')
else:
data = read(length)
log.write(' -> %r\n' % data)
log.flush()
except EOFError:
pass
finally:
if log != sys.stderr:
log.close()