diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index a58de7d..67d8837 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,66 +1,67 @@
-# Locate the source directory
+# Locate the source directories
 set(dir ${CMAKE_CURRENT_SOURCE_DIR})
+set(subdir "${dir}/fftpack")
 
 # The source files
 set(FFTPACK_SOURCES
-    ${dir}/cfftb1.f90
-    ${dir}/cfftf1.f90
-    ${dir}/cffti1.f90
-    ${dir}/cosqb1.f90
-    ${dir}/cosqf1.f90
-    ${dir}/dcosqb.f90
-    ${dir}/dcosqf.f90
-    ${dir}/dcosqi.f90
-    ${dir}/dcost.f90
-    ${dir}/dcosti.f90
-    ${dir}/dfftb.f90
-    ${dir}/dfftf.f90
-    ${dir}/dffti.f90
-    ${dir}/dsinqb.f90
-    ${dir}/dsinqf.f90
-    ${dir}/dsinqi.f90
-    ${dir}/dsint.f90
-    ${dir}/dsinti.f90
-    ${dir}/dzfftb.f90
-    ${dir}/dzfftf.f90
-    ${dir}/dzffti.f90
-    ${dir}/ezfft1.f90
+    ${subdir}/cfftb1.f90
+    ${subdir}/cfftf1.f90
+    ${subdir}/cffti1.f90
+    ${subdir}/cosqb1.f90
+    ${subdir}/cosqf1.f90
+    ${subdir}/dcosqb.f90
+    ${subdir}/dcosqf.f90
+    ${subdir}/dcosqi.f90
+    ${subdir}/dcost.f90
+    ${subdir}/dcosti.f90
+    ${subdir}/dfftb.f90
+    ${subdir}/dfftf.f90
+    ${subdir}/dffti.f90
+    ${subdir}/dsinqb.f90
+    ${subdir}/dsinqf.f90
+    ${subdir}/dsinqi.f90
+    ${subdir}/dsint.f90
+    ${subdir}/dsinti.f90
+    ${subdir}/dzfftb.f90
+    ${subdir}/dzfftf.f90
+    ${subdir}/dzffti.f90
+    ${subdir}/ezfft1.f90
     ${dir}/fftpack.f90
-    ${dir}/fftpack_dct.f90
-    ${dir}/fftpack_fft.f90
-    ${dir}/fftpack_fftshift.f90
-    ${dir}/fftpack_ifft.f90
-    ${dir}/fftpack_ifftshift.f90
-    ${dir}/fftpack_irfft.f90
-    ${dir}/fftpack_rfft.f90
-    ${dir}/fftpack_utils.f90
-    ${dir}/passb.f90
-    ${dir}/passb2.f90
-    ${dir}/passb3.f90
-    ${dir}/passb4.f90
-    ${dir}/passb5.f90
-    ${dir}/passf.f90
-    ${dir}/passf2.f90
-    ${dir}/passf3.f90
-    ${dir}/passf4.f90
-    ${dir}/passf5.f90
-    ${dir}/radb2.f90
-    ${dir}/radb3.f90
-    ${dir}/radb4.f90
-    ${dir}/radb5.f90
-    ${dir}/radbg.f90
-    ${dir}/radf2.f90
-    ${dir}/radf3.f90
-    ${dir}/radf4.f90
-    ${dir}/radf5.f90
-    ${dir}/radfg.f90
-    ${dir}/rfftb1.f90
-    ${dir}/rfftf1.f90
-    ${dir}/rffti1.f90
-    ${dir}/rk.f90
-    ${dir}/sint1.f90
-    ${dir}/zfftb.f90
-    ${dir}/zfftf.f90
-    ${dir}/zffti.f90
+    ${subdir}/fftpack_dct.f90
+    ${subdir}/fftpack_fft.f90
+    ${subdir}/fftpack_fftshift.f90
+    ${subdir}/fftpack_ifft.f90
+    ${subdir}/fftpack_ifftshift.f90
+    ${subdir}/fftpack_irfft.f90
+    ${subdir}/fftpack_rfft.f90
+    ${subdir}/fftpack_utils.f90
+    ${subdir}/passb.f90
+    ${subdir}/passb2.f90
+    ${subdir}/passb3.f90
+    ${subdir}/passb4.f90
+    ${subdir}/passb5.f90
+    ${subdir}/passf.f90
+    ${subdir}/passf2.f90
+    ${subdir}/passf3.f90
+    ${subdir}/passf4.f90
+    ${subdir}/passf5.f90
+    ${subdir}/radb2.f90
+    ${subdir}/radb3.f90
+    ${subdir}/radb4.f90
+    ${subdir}/radb5.f90
+    ${subdir}/radbg.f90
+    ${subdir}/radf2.f90
+    ${subdir}/radf3.f90
+    ${subdir}/radf4.f90
+    ${subdir}/radf5.f90
+    ${subdir}/radfg.f90
+    ${subdir}/rfftb1.f90
+    ${subdir}/rfftf1.f90
+    ${subdir}/rffti1.f90
+    ${subdir}/rk.f90
+    ${subdir}/sint1.f90
+    ${subdir}/zfftb.f90
+    ${subdir}/zfftf.f90
+    ${subdir}/zffti.f90
 )
 set(FFTPACK_SOURCES ${FFTPACK_SOURCES} PARENT_SCOPE)
diff --git a/src/Makefile b/src/fftpack/Makefile
similarity index 100%
rename from src/Makefile
rename to src/fftpack/Makefile
diff --git a/src/cfftb1.f90 b/src/fftpack/cfftb1.f90
similarity index 100%
rename from src/cfftb1.f90
rename to src/fftpack/cfftb1.f90
diff --git a/src/cfftf1.f90 b/src/fftpack/cfftf1.f90
similarity index 100%
rename from src/cfftf1.f90
rename to src/fftpack/cfftf1.f90
diff --git a/src/cffti1.f90 b/src/fftpack/cffti1.f90
similarity index 100%
rename from src/cffti1.f90
rename to src/fftpack/cffti1.f90
diff --git a/src/cosqb1.f90 b/src/fftpack/cosqb1.f90
similarity index 100%
rename from src/cosqb1.f90
rename to src/fftpack/cosqb1.f90
diff --git a/src/cosqf1.f90 b/src/fftpack/cosqf1.f90
similarity index 100%
rename from src/cosqf1.f90
rename to src/fftpack/cosqf1.f90
diff --git a/src/dcosqb.f90 b/src/fftpack/dcosqb.f90
similarity index 100%
rename from src/dcosqb.f90
rename to src/fftpack/dcosqb.f90
diff --git a/src/dcosqf.f90 b/src/fftpack/dcosqf.f90
similarity index 100%
rename from src/dcosqf.f90
rename to src/fftpack/dcosqf.f90
diff --git a/src/dcosqi.f90 b/src/fftpack/dcosqi.f90
similarity index 100%
rename from src/dcosqi.f90
rename to src/fftpack/dcosqi.f90
diff --git a/src/dcost.f90 b/src/fftpack/dcost.f90
similarity index 100%
rename from src/dcost.f90
rename to src/fftpack/dcost.f90
diff --git a/src/dcosti.f90 b/src/fftpack/dcosti.f90
similarity index 100%
rename from src/dcosti.f90
rename to src/fftpack/dcosti.f90
diff --git a/src/dfftb.f90 b/src/fftpack/dfftb.f90
similarity index 100%
rename from src/dfftb.f90
rename to src/fftpack/dfftb.f90
diff --git a/src/dfftf.f90 b/src/fftpack/dfftf.f90
similarity index 100%
rename from src/dfftf.f90
rename to src/fftpack/dfftf.f90
diff --git a/src/dffti.f90 b/src/fftpack/dffti.f90
similarity index 100%
rename from src/dffti.f90
rename to src/fftpack/dffti.f90
diff --git a/src/dsinqb.f90 b/src/fftpack/dsinqb.f90
similarity index 100%
rename from src/dsinqb.f90
rename to src/fftpack/dsinqb.f90
diff --git a/src/dsinqf.f90 b/src/fftpack/dsinqf.f90
similarity index 100%
rename from src/dsinqf.f90
rename to src/fftpack/dsinqf.f90
diff --git a/src/dsinqi.f90 b/src/fftpack/dsinqi.f90
similarity index 100%
rename from src/dsinqi.f90
rename to src/fftpack/dsinqi.f90
diff --git a/src/dsint.f90 b/src/fftpack/dsint.f90
similarity index 100%
rename from src/dsint.f90
rename to src/fftpack/dsint.f90
diff --git a/src/dsinti.f90 b/src/fftpack/dsinti.f90
similarity index 100%
rename from src/dsinti.f90
rename to src/fftpack/dsinti.f90
diff --git a/src/dzfftb.f90 b/src/fftpack/dzfftb.f90
similarity index 100%
rename from src/dzfftb.f90
rename to src/fftpack/dzfftb.f90
diff --git a/src/dzfftf.f90 b/src/fftpack/dzfftf.f90
similarity index 100%
rename from src/dzfftf.f90
rename to src/fftpack/dzfftf.f90
diff --git a/src/dzffti.f90 b/src/fftpack/dzffti.f90
similarity index 100%
rename from src/dzffti.f90
rename to src/fftpack/dzffti.f90
diff --git a/src/ezfft1.f90 b/src/fftpack/ezfft1.f90
similarity index 100%
rename from src/ezfft1.f90
rename to src/fftpack/ezfft1.f90
diff --git a/src/fftpack_dct.f90 b/src/fftpack/fftpack_dct.f90
similarity index 100%
rename from src/fftpack_dct.f90
rename to src/fftpack/fftpack_dct.f90
diff --git a/src/fftpack_fft.f90 b/src/fftpack/fftpack_fft.f90
similarity index 100%
rename from src/fftpack_fft.f90
rename to src/fftpack/fftpack_fft.f90
diff --git a/src/fftpack_fftshift.f90 b/src/fftpack/fftpack_fftshift.f90
similarity index 100%
rename from src/fftpack_fftshift.f90
rename to src/fftpack/fftpack_fftshift.f90
diff --git a/src/fftpack_ifft.f90 b/src/fftpack/fftpack_ifft.f90
similarity index 100%
rename from src/fftpack_ifft.f90
rename to src/fftpack/fftpack_ifft.f90
diff --git a/src/fftpack_ifftshift.f90 b/src/fftpack/fftpack_ifftshift.f90
similarity index 100%
rename from src/fftpack_ifftshift.f90
rename to src/fftpack/fftpack_ifftshift.f90
diff --git a/src/fftpack_irfft.f90 b/src/fftpack/fftpack_irfft.f90
similarity index 100%
rename from src/fftpack_irfft.f90
rename to src/fftpack/fftpack_irfft.f90
diff --git a/src/fftpack_rfft.f90 b/src/fftpack/fftpack_rfft.f90
similarity index 100%
rename from src/fftpack_rfft.f90
rename to src/fftpack/fftpack_rfft.f90
diff --git a/src/fftpack_utils.f90 b/src/fftpack/fftpack_utils.f90
similarity index 100%
rename from src/fftpack_utils.f90
rename to src/fftpack/fftpack_utils.f90
diff --git a/src/meson.build b/src/fftpack/meson.build
similarity index 100%
rename from src/meson.build
rename to src/fftpack/meson.build
diff --git a/src/passb.f90 b/src/fftpack/passb.f90
similarity index 100%
rename from src/passb.f90
rename to src/fftpack/passb.f90
diff --git a/src/passb2.f90 b/src/fftpack/passb2.f90
similarity index 100%
rename from src/passb2.f90
rename to src/fftpack/passb2.f90
diff --git a/src/passb3.f90 b/src/fftpack/passb3.f90
similarity index 100%
rename from src/passb3.f90
rename to src/fftpack/passb3.f90
diff --git a/src/passb4.f90 b/src/fftpack/passb4.f90
similarity index 100%
rename from src/passb4.f90
rename to src/fftpack/passb4.f90
diff --git a/src/passb5.f90 b/src/fftpack/passb5.f90
similarity index 100%
rename from src/passb5.f90
rename to src/fftpack/passb5.f90
diff --git a/src/passf.f90 b/src/fftpack/passf.f90
similarity index 100%
rename from src/passf.f90
rename to src/fftpack/passf.f90
diff --git a/src/passf2.f90 b/src/fftpack/passf2.f90
similarity index 100%
rename from src/passf2.f90
rename to src/fftpack/passf2.f90
diff --git a/src/passf3.f90 b/src/fftpack/passf3.f90
similarity index 100%
rename from src/passf3.f90
rename to src/fftpack/passf3.f90
diff --git a/src/passf4.f90 b/src/fftpack/passf4.f90
similarity index 100%
rename from src/passf4.f90
rename to src/fftpack/passf4.f90
diff --git a/src/passf5.f90 b/src/fftpack/passf5.f90
similarity index 100%
rename from src/passf5.f90
rename to src/fftpack/passf5.f90
diff --git a/src/radb2.f90 b/src/fftpack/radb2.f90
similarity index 100%
rename from src/radb2.f90
rename to src/fftpack/radb2.f90
diff --git a/src/radb3.f90 b/src/fftpack/radb3.f90
similarity index 100%
rename from src/radb3.f90
rename to src/fftpack/radb3.f90
diff --git a/src/radb4.f90 b/src/fftpack/radb4.f90
similarity index 100%
rename from src/radb4.f90
rename to src/fftpack/radb4.f90
diff --git a/src/radb5.f90 b/src/fftpack/radb5.f90
similarity index 100%
rename from src/radb5.f90
rename to src/fftpack/radb5.f90
diff --git a/src/radbg.f90 b/src/fftpack/radbg.f90
similarity index 100%
rename from src/radbg.f90
rename to src/fftpack/radbg.f90
diff --git a/src/radf2.f90 b/src/fftpack/radf2.f90
similarity index 100%
rename from src/radf2.f90
rename to src/fftpack/radf2.f90
diff --git a/src/radf3.f90 b/src/fftpack/radf3.f90
similarity index 100%
rename from src/radf3.f90
rename to src/fftpack/radf3.f90
diff --git a/src/radf4.f90 b/src/fftpack/radf4.f90
similarity index 100%
rename from src/radf4.f90
rename to src/fftpack/radf4.f90
diff --git a/src/radf5.f90 b/src/fftpack/radf5.f90
similarity index 100%
rename from src/radf5.f90
rename to src/fftpack/radf5.f90
diff --git a/src/radfg.f90 b/src/fftpack/radfg.f90
similarity index 100%
rename from src/radfg.f90
rename to src/fftpack/radfg.f90
diff --git a/src/rfftb1.f90 b/src/fftpack/rfftb1.f90
similarity index 100%
rename from src/rfftb1.f90
rename to src/fftpack/rfftb1.f90
diff --git a/src/rfftf1.f90 b/src/fftpack/rfftf1.f90
similarity index 100%
rename from src/rfftf1.f90
rename to src/fftpack/rfftf1.f90
diff --git a/src/rffti1.f90 b/src/fftpack/rffti1.f90
similarity index 100%
rename from src/rffti1.f90
rename to src/fftpack/rffti1.f90
diff --git a/src/rk.f90 b/src/fftpack/rk.f90
similarity index 100%
rename from src/rk.f90
rename to src/fftpack/rk.f90
diff --git a/src/sint1.f90 b/src/fftpack/sint1.f90
similarity index 100%
rename from src/sint1.f90
rename to src/fftpack/sint1.f90
diff --git a/src/zfftb.f90 b/src/fftpack/zfftb.f90
similarity index 100%
rename from src/zfftb.f90
rename to src/fftpack/zfftb.f90
diff --git a/src/zfftf.f90 b/src/fftpack/zfftf.f90
similarity index 100%
rename from src/zfftf.f90
rename to src/fftpack/zfftf.f90
diff --git a/src/zffti.f90 b/src/fftpack/zffti.f90
similarity index 100%
rename from src/zffti.f90
rename to src/fftpack/zffti.f90