diff --git a/doc/api.rst b/doc/api.rst
index 06c8a5533..d49b9b70e 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -8,6 +8,13 @@ migen API Documentation
         :members:
         :show-inheritance:
 
+:mod:`fhdl.size` Module
+------------------------------
+
+.. automodule:: migen.fhdl.size
+        :members:
+        :show-inheritance:
+
 :mod:`genlib.fifo` Module
 ------------------------------
 
diff --git a/migen/fhdl/size.py b/migen/fhdl/size.py
index a11690133..e771cccad 100644
--- a/migen/fhdl/size.py
+++ b/migen/fhdl/size.py
@@ -96,7 +96,103 @@ def value_bits_sign(v):
 		bsc = map(value_bits_sign, v.choices)
 		return max(bs[0] for bs in bsc), any(bs[1] for bs in bsc)
 	else:
-		raise TypeError
+		raise TypeError("Can not calculate bit length of {} {}".format(
+			type(v), v))
 
 def flen(v):
+	"""Bit length of an expression
+
+	Parameters
+	----------
+	v : int, bool or Value
+
+	Returns
+	-------
+	int
+		Number of bits required to store `v` or available in `v`
+
+	Examples
+	--------
+	>>> flen(f.Signal(8))
+	8
+	>>> flen(0xaa)
+	8
+	"""
 	return value_bits_sign(v)[0]
+
+def fiter(v):
+	"""Bit iterator
+
+	Parameters
+	----------
+	v : int, bool or Value
+
+	Returns
+	-------
+	iter
+		Iterator over the bits in `v`
+
+	Examples
+	--------
+	>>> list(fiter(f.Signal(2))) #doctest: +ELLIPSIS
+	[<migen.fhdl.structure._Slice object at 0x...>, <migen.fhdl.structure._Slice object at 0x...>]
+	>>> list(fiter(4))
+	[0, 0, 1]
+	"""
+	if isinstance(v, (bool, int)):
+		return ((v >> i) & 1 for i in range(bits_for(v)))
+	elif isinstance(v, f.Value):
+		return (v[i] for i in range(flen(v)))
+	else:
+		raise TypeError("Can not bit-iterate {} {}".format(type(v), v))
+
+def fslice(v, s):
+	"""Bit slice
+
+	Parameters
+	----------
+	v : int, bool or Value
+	s : slice or int
+
+	Returns
+	-------
+	int or Value
+		Expression for the slice `s` of `v`.
+
+	Examples
+	--------
+	>>> fslice(Signal(2), 1) #doctest: +ELLIPSIS
+	<migen.fhdl.structure._Slice object at 0x...>
+	>>> bin(fslice(0b1101, slice(1, None, 2)))
+	'0b10'
+	"""
+	if isinstance(v, (bool, int)):
+		if isinstance(s, int):
+			s = slice(s)
+		idx = range(*s.indices(flen(v)))
+		return sum(((v>>i) & 1) << j for j, i in enumerate(idx))
+	elif isinstance(v, f.Value):
+		return v[s]
+	else:
+		raise TypeError("Can not bit-slice {} {}".format(type(v), v))
+
+def freversed(v):
+	"""Bit reverse
+
+	Parameters
+	----------
+	v : int, bool or Value
+
+	Returns
+	-------
+	int or Value
+		Expression containing the bit reversed input.
+
+	Examples
+	--------
+	>>> freversed(Signal(2)) #doctest: +ELLIPSIS
+	<migen.fhdl.structure._Slice object at 0x...>
+	>>> bin(freversed(0b1011))
+	'0b1101'
+	"""
+	return fslice(v, slice(None, None, -1))
diff --git a/migen/fhdl/std.py b/migen/fhdl/std.py
index 3a4a3de51..b9ec729f3 100644
--- a/migen/fhdl/std.py
+++ b/migen/fhdl/std.py
@@ -1,5 +1,5 @@
 from migen.fhdl.structure import *
 from migen.fhdl.module import Module
 from migen.fhdl.specials import TSTriple, Instance, Memory
-from migen.fhdl.size import log2_int, bits_for, flen
+from migen.fhdl.size import log2_int, bits_for, flen, fiter, fslice, freversed
 from migen.fhdl.decorators import DecorateModule, InsertCE, InsertReset, RenameClockDomains
diff --git a/migen/test/test_size.py b/migen/test/test_size.py
new file mode 100644
index 000000000..07b305247
--- /dev/null
+++ b/migen/test/test_size.py
@@ -0,0 +1,45 @@
+import unittest
+
+from migen.fhdl.std import *
+
+class SignalSizeCase(unittest.TestCase):
+	def setUp(self):
+		self.i = 0xaa
+		self.j = -127
+		self.s = Signal((13, True))
+
+	def test_flen(self):
+		self.assertEqual(flen(self.s), 13)
+		self.assertEqual(flen(self.i), 8)
+		self.assertEqual(flen(self.j), 8)
+
+	def test_flen_type(self):
+		self.assertRaises(TypeError, flen, [])
+
+	def test_fiter(self):
+		for i, si in enumerate(fiter(self.s)):
+			self.assertEqual(si, self.s[i])
+		self.assertEqual(list(fiter(self.i)),
+				[(self.i >> i) & 1 for i in range(8)])
+		self.assertEqual(list(fiter(self.j)),
+				[(self.j >> i) & 1 for i in range(8)])
+
+	def test_fiter_type(self):
+		self.assertRaises(TypeError, fiter, [])
+
+	def test_fslice(self):
+		sl = slice(1, None, 2)
+		fslice(self.s, sl)
+		self.assertEqual(fslice(self.i, sl), 15)
+		self.assertEqual(fslice(self.j, sl), 8)
+
+	def test_fslice_type(self):
+		self.assertRaises(TypeError, fslice, [], 3)
+
+	def test_freversed(self):
+		freversed(self.s)
+		freversed(self.i)
+		freversed(self.j)
+
+	def test_freveseed_type(self):
+		self.assertRaises(TypeError, freversed, [])