Add support for building shared library with CMake (#291)

* Add support to build openlibm as a shared library using cmake by not compiling the C implementation when a native one exists

* Add CMake static and shared library build instruction and also added info about support for loongarch64

---------

Co-authored-by: Viral B. Shah <ViralBShah@users.noreply.github.com>

CMakeLists.txt

@@ -503,6 +503,32 @@ else()
 	message(FATAL_ERROR "${PROJECT_NAME} CMake build is not set up for ${OPENLIBM_ARCH_FOLDER}")
 endif()
 
+
+# Filter out C implementation from compilation list if a native implementation exists
+# when generating a shared library to avoid multiple definitions
+get_target_property(TARGET_TYPE "${PROJECT_NAME}" TYPE)
+if (TARGET_TYPE STREQUAL SHARED_LIBRARY)
+    foreach(FILE_TO_REMOVE ${OPENLIBM_ASM_SOURCE})
+        # Get filename and strip out extension
+        cmake_path(GET FILE_TO_REMOVE FILENAME FILENAME_TO_REMOVE)
+        cmake_path(REMOVE_EXTENSION FILENAME_TO_REMOVE OUTPUT_VARIABLE FILENAME_TO_REMOVE)
+        message(DEBUG "Filename to remove: ${FILENAME_TO_REMOVE}")
+
+        # Go through files and remove one with the same name
+        foreach(CUR_FILE ${OPENLIBM_C_SOURCE})
+            cmake_path(GET CUR_FILE FILENAME CUR_FILENAME)
+            cmake_path(REMOVE_EXTENSION CUR_FILENAME OUTPUT_VARIABLE CUR_FILENAME)
+
+            if(${CUR_FILENAME} STREQUAL ${FILENAME_TO_REMOVE})
+                list(REMOVE_ITEM OPENLIBM_C_SOURCE ${CUR_FILE})
+                message(DEBUG "Removed source file from compilation list: ${CUR_FILE}")
+                break()
+            endif()
+        endforeach()
+    endforeach()
+endif()
+
+
 # Add sources
 target_sources("${PROJECT_NAME}" PRIVATE ${OPENLIBM_C_SOURCE}
                                          ${OPENLIBM_ASM_SOURCE}

README.md

@@ -18,11 +18,13 @@ consistently across compilers and operating systems, and in 32-bit and
 OpenLibm builds on Linux, macOS, Windows, FreeBSD, OpenBSD, NetBSD, and
 DragonFly BSD.  It builds with both GCC and clang. Although largely
 tested and widely used on the x86 and x86-64 architectures, OpenLibm
-also supports arm, aarch64, ppc64le, mips, wasm32, riscv, s390(x), and
+also supports arm, aarch64, ppc64le, mips, wasm32, riscv, s390(x) and 
 loongarch64.
 
 ## Build instructions
 
+### GNU Make
+
 1. Use GNU Make to build OpenLibm. This is `make` on most systems, but `gmake` on BSDs.
 2. Use `make USEGCC=1` to build with GCC. This is the default on
    Linux and Windows.
@@ -34,6 +36,17 @@ loongarch64.
    i686. GCC 4.8 is the minimum requirement for correct codegen on
    older 32-bit architectures.
 
+### CMake
+
+1. Create build directory with `mkdir build` and navigate into it with `cd build`.
+2. Run CMake to configure project and generate native build system with `cmake /path/to/openlibm/`
+or generate project with build system of choice e.g. `cmake /path/to/openlib/ -G "MinGW Makefiles"`.
+3. Build with the build system with `cmake --build .`.
+
+Default CMake configuration builds a `STATIC` library. To build a `SHARED` library,
+replace the keyword the `add_library()`in the `CMakeLists.txt`.
+
+
 ## Acknowledgements
 
 PowerPC support for openlibm was graciously sponsored by IBM.