This is libtap, a a suite consisting of:
* tapencoder, a library for detection of zero-crossings of an audio signal
* tapdecoder, a generator of variable-length waves

Those libraries are distributed under the GNU Lesser General Public License.

It is possible to build it using GNU make and a compiler such as gcc.
Possible make targets are:
* tapencoder.dll (Windows version of tapencoder)
* tapdecoder.dll (Windows version of tapdecoder)
* libtapencoder.so (Unix version of tapencoder)
* libtapdecoder.so (Unix version of tapdecoder)

On Windows, MinGW (http://mingw.org) provides the tools necessary to build it.
On a command prompt which can access the MinGW tools, type

make

to build the default target, consisting of tapencoder.dll and tapdecoder.dll.
On all platforms, you can explicitly state the targets on make's command line.

Some modifiers:
* CC: changes the compiler. Examples:
  >make CC=gcc
   needed if your installation does not provide cc.
  >make CC=clang
   if you want to use LLVM instead of gcc (and LLVM is installed).
  >make CC=i586-mingw32msvc-gcc
   if you are running Linux and you want to produce Windows DLLs (and you have
   the MinGW cross-compiler installed)
* WITH_SINE: set to 1 to build sine waves into tapdecoder, when using
  glibc. Generation of sine waves requires a mathematical function whcih glibc
  only provides in a separate library. If your platform does not use glibc
  (e.g. Windows or Mac), this is not needed. Examples:
  >make libtapdecoder.so WITH_SINE=1
* CFLAGS: compiler flags
  For example, gcc and LLVM accept -g to build debug versions, which can be
  debugged using gdb. Examples:
  >make libtapencoder.so libtapdecoder.so CFLAGS=-g
   build debug versions of tapencoder and tapdecoder
  >make libtapencoder.so CFLAGS='-g -fPIC'
   When building for Linux 64-bit, the error
   'relocation R_X86_64_PC32 against undefined symbol `free@@GLIBC_2.2.5' can
   not be used when making a shared object; recompile with -fPIC' might
   occur. You need to add -fPIC to the compiler flags to avoid that.
* WITH_VERSION: set to 1 when creating Windows DLLs and want to add additional
  metadata to the file, such as version number and description, that can be
  seen by right-clicking on the file and choosing Properties, then Summary.
  This needs the windres tool: if it has a non-standard name, the modifier
  WINDRES can be used to specify the tool. Examples:
  >make tapdecoder.dll WITH_VERSION=1
  >make tapdecoder.dll CC=i586-mingw32msvc-gcc WINDRES=i586-mingw32msvc-windres WITH_VERSION=1
  (the latter on Unix using the MinGW cross-compiler)