control skipping white spaces before comments with strip.white

Author: ben-schwen

inst/tests/tests.Rraw

@@ -21769,3 +21769,11 @@ test(2341.21, fread('# meta1 # meta2
 a,b
 1,2', comment.char = '#'), data.table(a=1L, b=2L))
 test(2341.22, fread('a,b   # inline header comment\r\n1,2\r\n', comment.char = '#'), data.table(a=1L, b=2L))
+# control skipping white space before comments with strip.white
+test(2341.23, fread('a
+b  # trailing cmnt
+', comment.char = '#', strip.white = FALSE, sep = ","), data.table(a="b  "))
+test(2341.24, fread('a
+  # leading cmnt
+b
+', comment.char = '#', strip.white = FALSE, sep = ","), data.table(a=c("  ", "b")))

src/fread.c

@@ -273,9 +273,15 @@ static inline void skip_white(const char **pch)
  */
 static inline const char *skip_to_comment_or_nonwhite(const char *ch)
 {
-  while (ch < eof && (*ch == ' ' || *ch == '\t' || *ch == '\0')) {
-    if (commentChar && *ch == commentChar) break; // comment char might be space or tab
-    ch++;
+  while (ch < eof && *ch == '\0') ++ch;
+  if (!stripWhite) return ch;
+
+  const unsigned char stopSpace = (commentChar == ' ');
+  const unsigned char stopTab   = (commentChar == '\t');
+
+  while (ch < eof && (*ch == ' ' || *ch == '\t')) {
+    if ((stopSpace && *ch == ' ') || (stopTab && *ch == '\t')) break;
+    ++ch;
   }
   return ch;
 }