diff --git a/.waf-tools/pch.py b/.waf-tools/pch.py
index b4f8f7f..087d633 100644
--- a/.waf-tools/pch.py
+++ b/.waf-tools/pch.py
@@ -1,38 +1,144 @@
 #! /usr/bin/env python
 # encoding: utf-8
+# Alexander Afanasyev (UCLA), 2014
 
-from waflib import Logs, Utils, Task, TaskGen
-from waflib.Tools import c_preproc
+"""
+Enable precompiled C++ header support (currently only clang++ and g++ are supported)
+
+To use this tool, wscript should look like:
+
+	def options(opt):
+		opt.load('pch')
+		# This will add `--with-pch` configure option.
+		# Unless --with-pch during configure stage specified, the precompiled header support is disabled
+
+	def configure(conf):
+		conf.load('pch')
+		# this will set conf.env.WITH_PCH if --with-pch is specified and the supported compiler is used
+		# Unless conf.env.WITH_PCH is set, the precompiled header support is disabled
+
+	def build(bld):
+		bld(features='cxx pch',
+			target='precompiled-headers',
+			name='precompiled-headers',
+			headers='a.h b.h c.h', # headers to pre-compile into `precompiled-headers`
+
+			# Other parameters to compile precompiled headers
+			# includes=...,
+			# export_includes=...,
+			# use=...,
+			# ...
+
+			# Exported parameters will be propagated even if precompiled headers are disabled
+		)
+
+		bld(
+			target='test',
+			features='cxx cxxprogram',
+			source='a.cpp b.cpp d.cpp main.cpp',
+			use='precompiled-headers',
+		)
+
+		# or
+
+		bld(
+			target='test',
+			features='pch cxx cxxprogram',
+			source='a.cpp b.cpp d.cpp main.cpp',
+			headers='a.h b.h c.h',
+		)
+
+Note that precompiled header must have multiple inclusion guards.  If the guards are missing, any benefit of precompiled header will be voided and compilation may fail in some cases.
+"""
+
+import os
+from waflib import Task, TaskGen, Logs, Utils
+from waflib.Tools import c_preproc, cxx
+
+
+PCH_COMPILER_OPTIONS = {
+	'clang++': [['-include'], '.pch', ['-x', 'c++-header']],
+	'g++':     [['-include'], '.gch', ['-x', 'c++-header']],
+}
+
 
 def options(opt):
-    opt.add_option('--with-pch', action='store_true', default=False, dest='with_pch',
-                   help='''Try to use precompiled header to speed up compilation '''
-                        '''(only gcc and clang)''')
+	opt.add_option('--without-pch', action='store_false', default=True, dest='with_pch', help='''Try to use precompiled header to speed up compilation (only g++ and clang++)''')
 
 def configure(conf):
-    conf.env['WITH_PCH'] = conf.options.with_pch
+	if (conf.options.with_pch and conf.env['COMPILER_CXX'] in PCH_COMPILER_OPTIONS.keys()):
+		conf.env.WITH_PCH = True
+		flags = PCH_COMPILER_OPTIONS[conf.env['COMPILER_CXX']]
+		conf.env.CXXPCH_F = flags[0]
+		conf.env.CXXPCH_EXT = flags[1]
+		conf.env.CXXPCH_FLAGS = flags[2]
 
 
+@TaskGen.feature('pch')
+@TaskGen.before('process_source')
+def apply_pch(self):
+	if not self.env.WITH_PCH:
+		return
+
+	if getattr(self.bld, 'pch_tasks', None) is None:
+		self.bld.pch_tasks = {}
+
+        if getattr(self, 'headers', None) is None:
+		return
+
+	self.headers = self.to_nodes(self.headers)
+
+	if getattr(self, 'name', None):
+		try:
+			task = self.bld.pch_tasks[self.name]
+			self.bld.fatal("Duplicated 'pch' task with name %r" % self.name)
+		except KeyError:
+			pass
+
+	out = '%s.%d%s' % (self.target, self.idx, self.env['CXXPCH_EXT'])
+	out = self.path.find_or_declare(out)
+	task = self.create_task('gchx', self.headers, out)
+
+	# target should be an absolute path of `out`, but without precompiled header extension
+	task.target = out.abspath()[:-len(out.suffix())]
+
+        self.pch_task = task
+	if getattr(self, 'name', None):
+		self.bld.pch_tasks[self.name] = task
+
 @TaskGen.feature('cxx')
-@TaskGen.before('process_source')
-def process_pch(self):
-    if getattr(self, 'pch', ''):
-        # for now support only gcc-compatible things
-        if self.env['COMPILER_CXX'] == 'g++':
-            nodes = self.to_nodes(self.pch, path=self.path)
-            for x in nodes:
-                z = self.create_task('gchx', x, x.change_ext('.hpp.gch'))
-                z.orig_self = self
+@TaskGen.after_method('process_source', 'propagate_uselib_vars')
+def add_pch(self):
+	if not (self.env['WITH_PCH'] and getattr(self, 'use', None) and getattr(self, 'compiled_tasks', None) and getattr(self.bld, 'pch_tasks', None)):
+		return
+
+	pch = None
+	# find pch task, if any
+
+	if getattr(self, 'pch_task', None):
+		pch = self.pch_task
+	else:
+		for use in Utils.to_list(self.use):
+			try:
+				pch = self.bld.pch_tasks[use]
+			except KeyError:
+				pass
+
+	if pch:
+		for x in self.compiled_tasks:
+			x.env.append_value('CXXFLAGS', self.env['CXXPCH_F'] + [pch.target])
 
 class gchx(Task.Task):
-    run_str = '${CXX} -x c++-header ${CXXFLAGS} ${FRAMEWORKPATH_ST:FRAMEWORKPATH} ' + \
-                '${CPPPATH_ST:INCPATHS} ${DEFINES_ST:DEFINES} ' + \
-                '${CXX_SRC_F}${SRC} ${CXX_TGT_F}${TGT}'
-    scan    = c_preproc.scan
-    ext_out = ['.hpp']
-    color   = 'BLUE'
+	run_str = '${CXX} ${ARCH_ST:ARCH} ${CXXFLAGS} ${CPPFLAGS} ${CXXPCH_FLAGS} ${FRAMEWORKPATH_ST:FRAMEWORKPATH} ${CPPPATH_ST:INCPATHS} ${DEFINES_ST:DEFINES} ${CXXPCH_F:SRC} ${CXX_SRC_F}${SRC[0].abspath()} ${CXX_TGT_F}${TGT[0].abspath()}'
+	scan    = c_preproc.scan
+	color   = 'BLUE'
+	ext_out=['.h']
 
-    def post_run(self):
-        super(gchx, self).post_run()
-        self.orig_self.env['CXXFLAGS'] = ['-include', self.inputs[0].relpath()] + \
-                                         self.env['CXXFLAGS']
+	def runnable_status(self):
+		ret = Task.Task.runnable_status(self)
+		if ret == Task.SKIP_ME and self.env.CXX_NAME == 'clang':
+			t = os.stat(self.outputs[0].abspath()).st_mtime
+			for n in self.inputs:
+				if os.stat(n.abspath()).st_mtime > t:
+					return Task.RUN_ME
+		return ret