diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..5746d2d
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,12 @@
+Copyright (c) 2023 John Regan
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..b2dea67
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,117 @@
+.PHONY: all clean test
+
+CFLAGS = -fPIC -g -O0 -Wall -Wextra
+LDFLAGS =
+
+all: utest-byte utest-short utest-word utest-quad \
+     utest-byte-static utest-short-static utest-word-static utest-quad-static \
+     utest-byte-single utest-short-single utest-word-single utest-quad-single \
+	 utest-coverage bigint.o
+
+test: utest-byte utest-short utest-word utest-quad utest-byte-single utest-short-single utest-word-single utest-quad-single utest-coverage
+	./utest-byte >/dev/null 2>&1 || ./utest-byte
+	./utest-short >/dev/null 2>&1 || ./utest-short
+	./utest-word >/dev/null 2>&1 || ./utest-word
+	./utest-quad >/dev/null 2>&1 || ./utest-quad
+	./utest-byte-single >/dev/null 2>&1 || ./utest-byte-single
+	./utest-short-single >/dev/null 2>&1 || ./utest-short-single
+	./utest-word-single >/dev/null 2>&1 || ./utest-word-single
+	./utest-quad-single >/dev/null 2>&1 || ./utest-quad-single
+	./utest-byte-static >/dev/null 2>&1 || ./utest-byte-static
+	./utest-short-static >/dev/null 2>&1 || ./utest-short-static
+	./utest-word-static >/dev/null 2>&1 || ./utest-word-static
+	./utest-quad-static >/dev/null 2>&1 || ./utest-quad-static
+	mkdir -p coverage
+	rm -f coverage/*
+	./utest-coverage
+	gcovr --html-details --output coverage/index.html
+	rm -f *.gcda
+	rm -f *.gcno
+
+utest-byte: utest-byte.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-short: utest-short.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-word: utest-word.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-quad: utest-quad.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-byte-single: utest-byte-single.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-short-single: utest-short-single.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-word-single: utest-word-single.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-quad-single: utest-quad-single.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-byte-static: utest-byte-static.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-short-static: utest-short-static.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-word-static: utest-word-static.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-quad-static: utest-quad-static.o
+	$(CC) -o $@ $^ $(LDFLAGS)
+
+utest-coverage: utest-coverage.o
+	$(CC) -o $@ $^ $(LDFLAGS) --coverage
+
+utest-byte.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_WORD_WIDTH=1 -c -o $@ $<
+
+utest-short.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_WORD_WIDTH=2 -c -o $@ $<
+
+utest-word.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_WORD_WIDTH=4 -c -o $@ $<
+
+utest-quad.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_WORD_WIDTH=8 -c -o $@ $<
+
+utest-byte-single.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_SINGLE_WORD_ONLY -DBIGINT_WORD_WIDTH=1 -c -o $@ $<
+
+utest-short-single.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_SINGLE_WORD_ONLY -DBIGINT_WORD_WIDTH=2 -c -o $@ $<
+
+utest-word-single.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_SINGLE_WORD_ONLY -DBIGINT_WORD_WIDTH=4 -c -o $@ $<
+
+utest-quad-single.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_SINGLE_WORD_ONLY -DBIGINT_WORD_WIDTH=8 -c -o $@ $<
+
+utest-byte-static.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_NO_MALLOC -DBIGINT_WORD_WIDTH=1 -c -o $@ $<
+
+utest-short-static.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_NO_MALLOC -DBIGINT_WORD_WIDTH=2 -c -o $@ $<
+
+utest-word-static.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_NO_MALLOC -DBIGINT_WORD_WIDTH=4 -c -o $@ $<
+
+utest-quad-static.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) -DBIGINT_NO_MALLOC -DBIGINT_WORD_WIDTH=8 -c -o $@ $<
+
+utest-coverage.o: utest.c utest.h bigint.h
+	$(CC) $(CFLAGS) --coverage -c -o $@ $<
+
+bigint.o: bigint.h
+	$(CC) -DBIGINT_IMPLEMENTATION -std=c99 -pedantic $(CFLAGS) -c -o $@ $<
+
+clean:
+	rm -f *.o *.exe
+	rm -f utest-coverage
+	rm -f utest-byte utest-short utest-word utest-quad
+	rm -f utest-byte-single utest-short-single utest-word-single utest-quad-single
+	rm -f utest-byte-static utest-short-static utest-word-static utest-quad-static
diff --git a/bigint.h b/bigint.h
index eebb44f..1ac01cd 100644
--- a/bigint.h
+++ b/bigint.h
@@ -1,6 +1,21 @@
 #ifndef BIGINTH
 #define BIGINTH
 
+/*
+Copyright (c) 2023 John Regan
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.
+*/
+
 #if !defined(BIGINT_API)
     #ifdef _WIN32
         #define BIGINT_DLL_IMPORT  __declspec(dllimport)