update SystemRequirements again

DESCRIPTION

@@ -32,9 +32,7 @@ Suggests:
 LinkingTo: 
     cpp11
 SystemRequirements:
-    fftw (>= 3.3.0),
-    fftwf (>= 3.3.0),
-    fftw3f_omp
+    fftw3 (including single precision support fftw3f), fftw3f_omp (optional), OpenMP (optional)
 Config/testthat/edition: 3
 URL: https://lschneiderbauer.github.io/fCWTr/, https://github.com/lschneiderbauer/fCWTr
 Roxygen: list(markdown = TRUE)

configure

@@ -4274,7 +4274,7 @@ then :
   test "$ac_res" = "none required" || LIBS="$ac_res $LIBS"
   have_fftw=yes
 else case e in #(
-  e) as_fn_error $? "The fftw3f library is required." "$LINENO" 5
+  e) as_fn_error $? "The fftw3f library is required. In case fftw is already installed, you might need to enable fftw's single precision support with './configure --enable-float'." "$LINENO" 5
  ;;
 esac
 fi

configure.ac

@@ -41,7 +41,7 @@ AC_SEARCH_LIBS(
   fftwf_free,
   fftw3f,
   [have_fftw=yes],
-  [AC_MSG_ERROR([The fftw3f library is required.])]
+  [AC_MSG_ERROR([The fftw3f library is required. In case fftw is already installed, you might need to enable fftw's single precision support with './configure --enable-float'.])]
 )
 
 # Check for omp.h header

cran-comments.md

@@ -2,8 +2,8 @@
 
 This is a resubmission (after package being archived). In this version I have:
 
--   Changed 'SystemRequirements' to directly refer to single precission 'fftwf' and changed 'openmp' to 'fftwf_omp'.
--   I do not understand the comment 'does not test for [fftwf]': ./configure.ac, line #40, contains a paragraph that tests for single precision functions. The configuration fails with a descriptive error message "The fftw3f library is required." in case it does not find a fitting library. I searched the "Writing R Extensions" documentation for additional mandatory places, where a check should occur, to no avail.
+-   Changed 'SystemRequirements' to directly refer to single precision 'fftw3f' and added 'fftw3f_omp'. I also indicated the OpenMP requirement as optional. I removed version requirements (since '3' implies version 3).
+-   The comment "[The package] does not test for [fftwf]" seems incorrect to me: The file ./configure.ac, line #40, contains a paragraph that tests for single precision functions. The configuration fails with a descriptive error message "The fftw3f library is required." in case it does not find a fitting library. I now added additional information to this error message to make it more clear what is missing. I searched the "Writing R Extensions" documentation for additional mandatory places, where a check should occur, to no avail.
 -   I also added other features, unrelated to the comments, since last submission/archiving.
 
 ## R CMD check results