[Teem-commit] SF.net SVN: teem:[7380] teem/trunk/CMake/CheckLibM. cmake

[<kin...@us...>]

Revision: 7380
          http://sourceforge.net/p/teem/code/7380
Author:   kindlmann
Date:     2025-09-10 00:09:09 +0000 (Wed, 10 Sep 2025)
Log Message:
-----------
overblown test for needing -lm linking

Added Paths:
-----------
    teem/trunk/CMake/CheckLibM.cmake

Added: teem/trunk/CMake/CheckLibM.cmake
===================================================================
--- teem/trunk/CMake/CheckLibM.cmake	                        (rev 0)
+++ teem/trunk/CMake/CheckLibM.cmake	2025-09-10 00:09:09 UTC (rev 7380)
@@ -0,0 +1,141 @@
+# CMake/CheckLibM.cmake: learn if need to link with -lm for math functions
+# Copyright (C) 2025  University of Chicago
+# See ../LICENSE.txt for licensing terms
+
+### Rationale
+# Different unices have different ways of tacitly linking (or not) with -lm.
+# In the interests of pedantic explicitness, we figure out if, linking with -lm
+# is needed when linking with a library that calls math functions.  Yes,
+# https://cmake.org/cmake/help/latest/module/CheckLibraryExists.html could
+# probably do the job here, but once I (GLK) went down the rabbit hole of
+# understanding what the problem was, I wanted to create a CMake module that
+# replicated the minimal example I used. So, this test builds a shared library
+# `libtiny` that calls some math functions, then an executable `maintiny` that
+# calls into that library. When compiling `maintiny`, we try linking:
+#   1. Without -lm
+#   2. With -lm (if needed)
+# Then we run `maintiny` to ensure the math is mathing.
+#
+# Defines:
+#   LIBM_NEEDED -- TRUE if executables must link with -lm
+#
+# Usage example
+#   include(CheckLibM)
+#   if(LIBM_NEEDED)
+#     target_link_libraries(Teem PRIVATE m)
+#   endif()
+#
+
+### ------------------------------------------------------------------------
+# Setup
+if(DEFINED LIBM_NEEDED)
+  # not our first rodeo
+  return()
+endif()
+
+set(_lmn_desc "Does the platform require linking with -lm?")
+message(STATUS "CheckLibM: ${_lmn_desc}")
+
+set(_checklibm_dir "${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/tmpCheckLibM")
+file(MAKE_DIRECTORY "${_checklibm_dir}")
+
+# write `tiny.c`: single source file for libtiny, using some functions that very
+# likely do *not* exist outside the standard math library: tanf and log1pf.
+# Will evaluate with val=1.5703125, but not at compile time or else optimizer
+# will happily pre-compute the result, thus undermining this test.
+# T=log1pf(tanf(1.5703125)) ~= 7.634267208876022, so RT=(int)T should be 7
+# If 7 == RT, our exit status should be unix for "all good", i.e. 0 ==> return 7 != T
+file(WRITE "${_checklibm_dir}/tiny.c" "
+#include <math.h>
+int tinyFunc(double val) {
+  return (7 != (int)(log1pf(tanf(val))));
+}
+")
+
+# write `maintiny.c`: single source for main() that calls into libtiny
+file(WRITE "${_checklibm_dir}/maintiny.c" "
+extern int tinyFunc(double val);
+int main(void) {
+  return tinyFunc(1.5703125f);
+}
+")
+
+# big helper macro to build & run test project
+macro(_checklibm_try_build_and_run _suffix _extra_libs _result_var)
+  set(_proj_dir "${_checklibm_dir}/${_suffix}")
+  file(MAKE_DIRECTORY "${_proj_dir}")
+
+  # write a minimal CMake project
+  file(WRITE "${_proj_dir}/CMakeLists.txt" "
+cmake_minimum_required(VERSION 3.13)
+project(CheckLibM_${_suffix} C)
+
+add_library(tiny SHARED \"${_checklibm_dir}/tiny.c\")
+add_executable(maintiny \"${_checklibm_dir}/maintiny.c\")
+target_link_libraries(maintiny PRIVATE tiny ${_extra_libs})
+  ")
+
+  try_compile(_${_suffix}_ok
+    "${_proj_dir}/build"
+    "${_proj_dir}"
+    CheckLibM_${_suffix}
+    OUTPUT_VARIABLE _${_suffix}_out
+  )
+
+  if(_${_suffix}_ok)
+    # Run the resulting binary to check runtime
+    set(_bin "${_proj_dir}/build/maintiny${CMAKE_EXECUTABLE_SUFFIX}")
+    if(EXISTS "${_bin}")
+      execute_process(
+        COMMAND "${_bin}"
+        RESULT_VARIABLE _${_suffix}_runres
+        OUTPUT_VARIABLE _${_suffix}_runout
+        ERROR_VARIABLE  _${_suffix}_runerr
+      )
+      if(_${_suffix}_runres EQUAL 0)
+        set(${_result_var} TRUE PARENT_SCOPE)
+      else()
+        message(FATAL_ERROR
+          "CheckLibM: maintiny built in ${_suffix} mode but failed at runtime.\n"
+          "Exit code: ${_${_suffix}_runres}\n"
+          "Stdout: ${_${_suffix}_runout}\n"
+          "Stderr: ${_${_suffix}_runerr}")
+      endif()
+    else()
+      message(FATAL_ERROR "CheckLibM: maintiny executable missing in ${_suffix} test")
+    endif()
+  else()
+    set(${_result_var} FALSE PARENT_SCOPE)
+  endif()
+endmacro()
+
+### ------------------------------------------------------------------------
+# Now run the test.
+# First try compiling + running without `-lm` ...
+_checklibm_try_build_and_run(no_libm "" _checklibm_no_libm_ok)
+
+if(_checklibm_no_libm_ok)
+  # ... and either it did work without `-lm`, or ...
+  set(LIBM_NEEDED FALSE CACHE BOOL ${_lmn_desc})
+  message(STATUS "CheckLibM: math works without -lm")
+else()
+  # ... it did not work without -lm.
+  # Does it does work *with* -lm?
+  _checklibm_try_build_and_run(with_libm "m" _checklibm_with_libm_ok)
+
+  if(_checklibm_with_libm_ok)
+    # Yes, it does work with -lm.
+    set(LIBM_NEEDED TRUE CACHE BOOL "${_lmn_desc}")
+    message(STATUS "CheckLibM: math requires explicit -lm")
+  else()
+    # Yikes, it failed without and with -lm. Bye.
+    message(FATAL_ERROR
+      "CheckLibM: math test failed even with -lm. Output:\n"
+      "${_checklibm_no_libm_out}\n"
+      "${_checklibm_with_libm_out}")
+  endif()
+endif()
+
+### ------------------------------------------------------------------------
+# Cleanup
+file(REMOVE_RECURSE "${_checklibm_dir}")

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