use AS_VERSION_COMPARE helper

Author: kevinushey

configure

@@ -552,6 +552,66 @@ as_tr_cpp="eval sed 'y%*$as_cr_letters%P$as_cr_LETTERS%;s%[^_$as_cr_alnum]%_%g'"
 # Sed expression to map a string onto a valid variable name.
 as_tr_sh="eval sed 'y%*+%pp%;s%[^_$as_cr_alnum]%_%g'"
 
+as_awk_strverscmp='
+  # Use only awk features that work with 7th edition Unix awk (1978).
+  # My, what an old awk you have, Mr. Solaris!
+  END {
+    while (length(v1) && length(v2)) {
+      # Set d1 to be the next thing to compare from v1, and likewise for d2.
+      # Normally this is a single character, but if v1 and v2 contain digits,
+      # compare them as integers and fractions as strverscmp does.
+      if (v1 ~ /^[0-9]/ && v2 ~ /^[0-9]/) {
+	# Split v1 and v2 into their leading digit string components d1 and d2,
+	# and advance v1 and v2 past the leading digit strings.
+	for (len1 = 1; substr(v1, len1 + 1) ~ /^[0-9]/; len1++) continue
+	for (len2 = 1; substr(v2, len2 + 1) ~ /^[0-9]/; len2++) continue
+	d1 = substr(v1, 1, len1); v1 = substr(v1, len1 + 1)
+	d2 = substr(v2, 1, len2); v2 = substr(v2, len2 + 1)
+	if (d1 ~ /^0/) {
+	  if (d2 ~ /^0/) {
+	    # Compare two fractions.
+	    while (d1 ~ /^0/ && d2 ~ /^0/) {
+	      d1 = substr(d1, 2); len1--
+	      d2 = substr(d2, 2); len2--
+	    }
+	    if (len1 != len2 && ! (len1 && len2 && substr(d1, 1, 1) == substr(d2, 1, 1))) {
+	      # The two components differ in length, and the common prefix
+	      # contains only leading zeros.  Consider the longer to be less.
+	      d1 = -len1
+	      d2 = -len2
+	    } else {
+	      # Otherwise, compare as strings.
+	      d1 = "x" d1
+	      d2 = "x" d2
+	    }
+	  } else {
+	    # A fraction is less than an integer.
+	    exit 1
+	  }
+	} else {
+	  if (d2 ~ /^0/) {
+	    # An integer is greater than a fraction.
+	    exit 2
+	  } else {
+	    # Compare two integers.
+	    d1 += 0
+	    d2 += 0
+	  }
+	}
+      } else {
+	# The normal case, without worrying about digits.
+	d1 = substr(v1, 1, 1); v1 = substr(v1, 2)
+	d2 = substr(v2, 1, 1); v2 = substr(v2, 2)
+      }
+      if (d1 < d2) exit 1
+      if (d1 > d2) exit 2
+    }
+    # Beware Solaris /usr/xgp4/bin/awk (at least through Solaris 10),
+    # which mishandles some comparisons of empty strings to integers.
+    if (length(v2)) exit 1
+    if (length(v1)) exit 2
+  }
+'
 
 test -n "$DJDIR" || exec 7<&0 </dev/null
 exec 6>&1
@@ -1669,12 +1729,19 @@ if test -z "${R_HOME}"; then
 fi
 
 R_VERSION=`"${R_HOME}/bin/R" --vanilla --slave -e "cat(as.character(getRversion()))"`
-if test "${R_VERSION}" \< "3.4.0"; then
-  R_CXX11_PREFIX="CXX1X"
-else
-  R_CXX11_PREFIX="CXX11"
-fi
-
+as_arg_v1="${R_VERSION}"
+as_arg_v2="3.4.0"
+awk "$as_awk_strverscmp" v1="$as_arg_v1" v2="$as_arg_v2" /dev/null
+case $? in #(
+  1) :
+    R_CXX11_PREFIX="CXX1X" ;; #(
+  0) :
+    R_CXX11_PREFIX="CXX11" ;; #(
+  2) :
+    R_CXX11_PREFIX="CXX11" ;; #(
+  *) :
+     ;;
+esac
 
 ac_config_files="$ac_config_files src/Makevars"
 

configure.ac

@@ -6,12 +6,10 @@ if test -z "${R_HOME}"; then
 fi
 
 R_VERSION=`"${R_HOME}/bin/R" --vanilla --slave -e "cat(as.character(getRversion()))"`
-if test "${R_VERSION}" \< "3.4.0"; then
-  R_CXX11_PREFIX="CXX1X"
-else
-  R_CXX11_PREFIX="CXX11"
-fi
-
+AS_VERSION_COMPARE("${R_VERSION}", "3.4.0",
+                   [R_CXX11_PREFIX="CXX1X"],
+                   [R_CXX11_PREFIX="CXX11"],
+                   [R_CXX11_PREFIX="CXX11"])
 AC_SUBST(R_CXX11_PREFIX)
 AC_CONFIG_FILES([src/Makevars])
 AC_OUTPUT