ed: edInsert() mostly duplicate code (#466)

* edInsert() handles Append "a" command and Insert "i" command
* The special case for address 0 can be removed; the code with tmp_lines2 is general enough to handle this, i.e. for address 0, tmp_lines will be added at start of buffer and tmp_lines2 will be empty
* In insert mode the target address is the addressed line; decrement is needed for conversion to correct array index
* test1: "0a", "0i" and "1i" --> add input to start of buffer
* test2: "1a" and "2i" --> add input after buffer line 1, and at buffer line 2 (equivalent)

bin/ed

@@ -780,37 +780,15 @@ sub edInsert {
         $tmp_chars += length;
     }
 
-    # now that we've got it, figure out what to do with it
-
-    if ($Mode == $INSERT_MODE) {
-
-        shift @lines; # get rid of 0 line
-        if ($adrs[0] == 0 || $adrs[0] == 1) {
-            unshift(@lines,@tmp_lines);
-            $CurrentLineNum = scalar(@tmp_lines);
-        } else {
-            @tmp_lines2 = splice(@lines,0,$adrs[0]-1);
-            unshift(@lines,@tmp_lines);
-            unshift(@lines,@tmp_lines2);
-            $CurrentLineNum = $adrs[0] + scalar(@tmp_lines) - 1;
-        }
-        unshift @lines, undef; # put 0 line back
-
-    } elsif ($Mode == $APPEND_MODE) {
-
-        shift(@lines); # get rid of 0 line
-        if ($adrs[0] == 0) {
-            unshift(@lines,@tmp_lines);
-            $CurrentLineNum = scalar(@tmp_lines);
-        } else {
-            @tmp_lines2 = splice(@lines,0,$adrs[0]);
-            unshift(@lines,@tmp_lines);
-            unshift(@lines,@tmp_lines2);
-            $CurrentLineNum = $adrs[0] + scalar(@tmp_lines);
-        }
-        unshift(@lines,undef); # put 0 line back
-
-    }
+    my $src = $adrs[0];
+    $src-- if ($src && $Mode == $INSERT_MODE);
+
+    shift @lines; # get rid of 0 line
+    @tmp_lines2 = splice @lines, 0, $src;
+    unshift @lines, @tmp_lines;
+    unshift @lines, @tmp_lines2;
+    $CurrentLineNum = $src + scalar(@tmp_lines);
+    unshift @lines, undef; # put 0 line back
 
     if ($tmp_chars) {
         $NeedToSave = 1;