diff --git a/src/base/SConscript b/src/base/SConscript
index 89a8dce..ca81822 100644
--- a/src/base/SConscript
+++ b/src/base/SConscript
@@ -37,6 +37,7 @@
 Source('atomicio.cc')
 GTest('atomicio.test', 'atomicio.test.cc', 'atomicio.cc')
 Source('bitfield.cc')
+GTest('bitfield.test', 'bitfield.test.cc', 'bitfield.cc')
 Source('imgwriter.cc')
 Source('bmpwriter.cc')
 Source('callback.cc')
diff --git a/src/base/bitfield.hh b/src/base/bitfield.hh
index f289396..08e3d2c 100644
--- a/src/base/bitfield.hh
+++ b/src/base/bitfield.hh
@@ -117,7 +117,14 @@
 }
 
 /**
- * Return val with bits first to last set to bit_val
+ * Returns val with bits first to last set to the LSBs of bit_val
+ *
+ * E.g.:
+ * first: 7
+ * last:  4
+ * val:      0xFFFF
+ * bit_val:  0x0000
+ * returned: 0xFF0F
  */
 template <class T, class B>
 inline
diff --git a/src/base/bitfield.test.cc b/src/base/bitfield.test.cc
new file mode 100644
index 0000000..0ee2a51
--- /dev/null
+++ b/src/base/bitfield.test.cc
@@ -0,0 +1,409 @@
+/*
+ * Copyright (c) 2019 The Regents of the University of California
+ * All rights reserved
+ *
+ * The license below extends only to copyright in the software and shall
+ * not be construed as granting a license to any other intellectual
+ * property including but not limited to intellectual property relating
+ * to a hardware implementation of the functionality of the software
+ * licensed hereunder.  You may use the software subject to the license
+ * terms below provided that you ensure that this notice is replicated
+ * unmodified and in its entirety in all distributions of the software,
+ * modified or unmodified, in source code or in binary form.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Bobby R. Bruce
+ */
+
+#include <gtest/gtest.h>
+
+#include "base/bitfield.hh"
+
+/*
+ * The following tests the "mask(N)" function. It is assumed that the mask
+ * returned is a 64 bit value with the N LSBs set to one.
+ */
+TEST(BitfieldTest, Mask0Bits)
+{
+    EXPECT_EQ(0x0, mask(0));
+}
+
+TEST(BitfieldTest, Mask1Bit)
+{
+    EXPECT_EQ(0x1, mask(1));
+}
+
+TEST(BitfieldTest, Mask8Bits)
+{
+    EXPECT_EQ(0xFF, mask(8));
+}
+
+TEST(BitfieldTest, Mask16Bits)
+{
+    EXPECT_EQ(0xFFFF, mask(16));
+}
+
+TEST(BitfieldTest, Mask32Bits)
+{
+    EXPECT_EQ(0xFFFFFFFF, mask(32));
+}
+
+TEST(BitfieldTest, MaskAllBits)
+{
+    EXPECT_EQ(0xFFFFFFFFFFFFFFFF, mask(64));
+}
+
+TEST(BitfieldTest, MaskAllBitsGreaterThan64)
+{
+    /* We cannot create a mask greater than 64 bits. It should default to 64
+     * bits if this occurs.
+     */
+    EXPECT_EQ(0xFFFFFFFFFFFFFFFF, mask(70));
+}
+
+/*
+ * The following tests "mask(X, Y)". mask will create a 64 bit value with bits
+ * X to Y (inclusive) set to one.
+ */
+TEST(BitfieldTest, MaskOneBit)
+{
+    EXPECT_EQ(1, mask(0,0));
+}
+
+TEST(BitfieldTest, MaskTwoBits)
+{
+    EXPECT_EQ((1 << 1) + 1, mask(1,0));
+}
+
+TEST(BitfieldTest, MaskThreeBits)
+{
+    EXPECT_EQ((1 << 5) + (1 << 4) + (1 << 3), mask(5,3));
+}
+
+TEST(BitfieldTest, MaskEntireRange)
+{
+    EXPECT_EQ(0xFFFFFFFFFFFFFFFF, mask(63,0));
+}
+
+TEST(BitfieldTest, MaskOutsideOfRange)
+{
+    // Masking >64 bits is not possible. The maximum is a 64 bit mask.
+    EXPECT_EQ(0xFFFFFFFFFFFFFFFF, mask(100, 0));
+}
+
+/*
+ * The following tests "bits". This function extracts bit/bits from the input
+ * value and return them as the LSBs. The remaining bits are set to zero.
+ */
+TEST(BitfieldTest, ExtractOneBit)
+{
+    int32_t x = 1 << 31;
+    EXPECT_EQ(1, bits(x, 31));
+}
+
+TEST(BitfieldTest, Extract63rdBit)
+{
+    int64_t x = 1ULL << 63;
+    EXPECT_EQ(1, bits(x, 63));
+}
+
+TEST(BitfieldTest, ExtractFirstBit)
+{
+    int64_t x = 1;
+    EXPECT_EQ(1, bits(x, 0));
+}
+
+TEST(BitfieldTest, ExtractFirstBitFirstBitZero)
+{
+    int64_t x = 1 << 1;
+    EXPECT_EQ(0, bits(x, 0));
+}
+
+TEST(BitfieldTest, ExtractThreeBits)
+{
+    uint64_t x = 1 << 31;
+    EXPECT_EQ((1 << 2), bits(x, 31, 29));
+}
+
+
+/*
+ * The following tests "mbits(X, Y, Z)". mbits returns a value with bits Y to
+ * Z from X (in position Y to Z).
+ */
+TEST(BitfieldTest, MbitsStandardCase)
+{
+    uint64_t x = (1 << 10) + (1 << 1);
+    EXPECT_EQ((1 << 10), mbits(x, 10, 8));
+}
+
+TEST(BitfieldTest, MbitsEntireRange)
+{
+    uint64_t x = (1ULL << 63) + 1;
+    EXPECT_EQ((1ULL << 63) + 1, mbits(x, 63, 0));
+}
+
+/*
+ * The following tests the "sext<N>(X)" function. sext carries out a sign
+ * extention from N bits to 64 bits on value X.
+ */
+TEST(BitfieldTest, SignExtendPositiveInput)
+{
+    int8_t val = 14;
+    int64_t output = 14;
+    EXPECT_EQ(output, sext<8>(val));
+}
+
+TEST(BitfieldTest, SignExtendNegativeInput)
+{
+    int8_t val = -14;
+    uint64_t output = -14;
+    EXPECT_EQ(output, sext<8>(val));
+}
+
+TEST(BitfieldTest, SignExtendPositiveInputOutsideRange)
+{
+    EXPECT_EQ((1 << 10), sext<8>(1 << 10));
+}
+
+TEST(BitfieldTest, SignExtendNegativeInputOutsideRange)
+{
+    uint64_t val = 0x4800000010000008;
+    uint64_t output = 0xF800000010000008;
+    EXPECT_EQ(output, sext<60>(val));
+}
+
+/* The following tests "insertBits(A, B, C, D)". insertBits returns A
+ * with bits B to C set to D's (B - C) LSBs. "insertBits(A, B, D)" overrides
+ * the function to insert only B's LSB to position B.
+ */
+TEST(BitfieldTest, InsertOneBitTo3)
+{
+    int64_t val = 0;
+    int64_t bits = (1 << 3) + (1 << 2) + (1 << 1) + 1;
+    EXPECT_EQ((1 << 3), insertBits(val, 3, bits));
+}
+
+TEST(BitfieldTest, InsertOneBitTo18)
+{
+    int64_t val = 0;
+    int64_t bits = (1 << 3) + (1 << 2) + (1 << 1) + 1;
+    EXPECT_EQ((1 << 18), insertBits(val, 18, bits));
+}
+
+TEST(BitfieldTest, InsertOneBitTo3LsbZero)
+{
+    int64_t val = 0;
+    int64_t bits = (1 << 3) + (1 << 2) + (1 << 1);
+    EXPECT_EQ(0, insertBits(val, 3, bits));
+}
+
+TEST(BitfieldTest, InsertOneBitTo18LsbZero)
+{
+    int64_t val = 0;
+    int64_t bits = (1 << 3) + (1 << 2) + (1 << 1);
+    EXPECT_EQ(0, insertBits(val, 18, bits));
+}
+
+TEST(BitfieldTest, InsertOnBitTo8LsbZero)
+{
+    int64_t val = (1 << 8);
+    int64_t bits = (1 << 3) + (1 << 2) + (1 << 1);
+    EXPECT_EQ(0, insertBits(val, 8, bits));
+}
+
+TEST(BitfieldTest, InsertMultipleBits)
+{
+    int64_t val = (1ULL << 63);
+    int64_t bits = (1 << 2) + 1;
+    EXPECT_EQ(val + (1 << 5) + (1 << 3), insertBits(val, 5, 3, bits));
+}
+
+TEST(BitfieldTest, InsertMultipleBitsOverwrite)
+{
+    int64_t val = (1 << 29);
+    int64_t bits = (1 << 2) + 1;
+    EXPECT_EQ((1 << 30) + (1 << 28), insertBits(val, 30, 28, bits));
+}
+
+// The following tests the "reverseBits" function.
+TEST(BitfieldTest, ReverseBits8Bit)
+{
+    uint8_t value = (1 << 7);
+    EXPECT_EQ(1, reverseBits(value));
+}
+
+TEST(BitfieldTest, ReverseBits64Bit)
+{
+    uint64_t value = 0xF0F0F0F0F0F0F0F1;
+    EXPECT_EQ(0x8F0F0F0F0F0F0F0F, reverseBits(value));
+}
+
+/* The following tests "findMsb" and "findLsb". These return the most position
+ * of the MSBs/LSBs of the input value.
+ */
+TEST(BitfieldTest, FindMsb29)
+{
+    uint64_t val = (1 << 29) + (1 << 1);
+    EXPECT_EQ(29, findMsbSet(val));
+}
+
+TEST(BitfieldTest, FindMsb63)
+{
+    uint64_t val = (1ULL << 63) + (1ULL << 60) + (1 << 1);
+    EXPECT_EQ(63, findMsbSet(val));
+}
+
+
+TEST(BitfieldTest, FindMsbZero)
+{
+    EXPECT_EQ(0, findMsbSet(0));
+}
+
+TEST(BitfieldTest, FindLsb)
+{
+    uint64_t val = (1ULL << 63) + (1 << 1);
+    EXPECT_EQ(1, findLsbSet(val));
+}
+
+TEST(BitfieldTest, FindLsbZero)
+{
+    EXPECT_EQ(64, findLsbSet(0));
+}
+
+/* The following tests a simple function that verifies whether a value is a
+ * a power of two or not.
+ */
+TEST(BitfieldTest, IsPow2)
+{
+    EXPECT_TRUE(isPow2(32));
+}
+
+TEST(BitfieldTest, IsNotPow2)
+{
+    EXPECT_FALSE(isPow2(36));
+}
+
+TEST(BitfieldTest, IsPow2Zero)
+{
+    EXPECT_TRUE(isPow2(0));
+}
+
+/*
+ * The following tests "popCount(X)". popCount counts the number of bits set to
+ * one.
+ */
+TEST(BitfieldTest, PopCountNoBits)
+{
+    EXPECT_EQ(0, popCount(0));
+}
+
+TEST(BitfieldTest, PopCountOneBit)
+{
+    int64_t val = (1 << 9);
+    EXPECT_EQ(1, popCount(val));
+}
+
+TEST(BitfieldTest, PopCountManyBits)
+{
+    int64_t val = (1 << 22) + (1 << 21) + (1 << 15) + (1 << 9) + 1;
+    EXPECT_EQ(5, popCount(val));
+}
+
+TEST(BitfieldTest, PopCountAllOnes)
+{
+    int64_t val = 0xFFFFFFFFFFFFFFFF;
+    EXPECT_EQ(64, popCount(val));
+}
+
+/*
+ * The following tests the "alignToPowerOfTwo(x)" function which rounds
+ * uint64_t x up to the nearest power of two. If x is already a power
+ * of two, that power is returned.
+ */
+TEST(BitfieldTest, AlignToPowerOfTwo0)
+{
+    EXPECT_EQ(0, alignToPowerOfTwo(0));
+}
+
+TEST(BitfieldTest, AlignToPowerOfTwo3)
+{
+    EXPECT_EQ(4, alignToPowerOfTwo(3));
+}
+
+TEST(BitfieldTest, AlignToPowerOfTwo5)
+{
+    EXPECT_EQ(8, alignToPowerOfTwo(5));
+}
+
+TEST(BitfieldTest, AlignToPowerOfTwo10)
+{
+    EXPECT_EQ(16, alignToPowerOfTwo(10));
+}
+
+TEST(BitfieldTest, AlignToPowerOfTwo16)
+{
+    EXPECT_EQ(16, alignToPowerOfTwo(16));
+}
+
+TEST(BitfieldTest, AlignToPowerOfTwo31)
+{
+    EXPECT_EQ(32, alignToPowerOfTwo(31));
+}
+
+/*
+ * The following tests test ctz32/64. The value returned in all cases should
+ * be equal to the number of trailing zeros (i.e., the number before the first
+ * bit set to one).
+ */
+
+TEST(BitfieldTest, CountTrailingZeros32BitsNoTrailing)
+{
+    int32_t value = 1;
+    EXPECT_EQ(0, ctz32(value));
+}
+
+TEST(BitfieldTest, CountTrailingZeros32Bits)
+{
+    uint32_t value = (1 << 30) + (1 << 29);
+    EXPECT_EQ(29, ctz32(value));
+}
+
+TEST(BitfieldTest, CountTrailingZeros64BitsNoTrailing)
+{
+    uint64_t value = (1 << 29) + 1;
+    EXPECT_EQ(0, ctz64(value));
+}
+
+TEST(BitfieldTest, CountTrailingZeros64Bits)
+{
+    uint64_t value = 1ULL << 63;
+    EXPECT_EQ(63, ctz64(value));
+}
+
+TEST(BitfieldTest, CountTrailingZero64AllZeros)
+{
+    uint64_t value = 0;
+    EXPECT_EQ(64, ctz64(value));
+}
\ No newline at end of file