whitespace: correct bit assignment comments

A comment in diff.c claimed that bits up to 12th (counting from 0th)
are whitespace rules, and 13th thru 15th are for new/old/context,
but it turns out it was miscounting.  Correct them, and clarify
where the whitespace rule bits come from in the comment.  Extend bit
assignment comments to cover bits used for color-moved, which
weren't described.

Also update the way these bit constants are defined to use (1 << N)
notation, instead of octal constants, as it tends to make it easier
to notice a breakage like this.

Sprinkle a few blank lines between logically distinct groups of CPP
macro definitions to make them easier to read.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: gitster

diff.c

@@ -801,16 +801,19 @@ enum diff_symbol {
 	DIFF_SYMBOL_CONTEXT_MARKER,
 	DIFF_SYMBOL_SEPARATOR
 };
+
 /*
  * Flags for content lines:
- * 0..12 are whitespace rules
- * 13-15 are WSEH_NEW | WSEH_OLD | WSEH_CONTEXT
+ * 0..11 are whitespace rules (see ws.h)
+ * 12..14 are WSEH_NEW | WSEH_CONTEXT | WSEH_OLD
  * 16 is marking if the line is blank at EOF
+ * 17..19 are used for color-moved.
  */
 #define DIFF_SYMBOL_CONTENT_BLANK_LINE_EOF	(1<<16)
 #define DIFF_SYMBOL_MOVED_LINE			(1<<17)
 #define DIFF_SYMBOL_MOVED_LINE_ALT		(1<<18)
 #define DIFF_SYMBOL_MOVED_LINE_UNINTERESTING	(1<<19)
+
 #define DIFF_SYMBOL_CONTENT_WS_MASK (WSEH_NEW | WSEH_OLD | WSEH_CONTEXT | WS_RULE_MASK)
 
 /*

diff.h

@@ -331,9 +331,9 @@ struct diff_options {
 
 	int ita_invisible_in_index;
 /* white-space error highlighting */
-#define WSEH_NEW (1<<12)
-#define WSEH_CONTEXT (1<<13)
-#define WSEH_OLD (1<<14)
+#define WSEH_NEW        (1<<12)
+#define WSEH_CONTEXT    (1<<13)
+#define WSEH_OLD        (1<<14)
 	unsigned ws_error_highlight;
 	const char *prefix;
 	int prefix_length;

ws.h

@@ -7,19 +7,22 @@ struct strbuf;
 /*
  * whitespace rules.
  * used by both diff and apply
- * last two digits are tab width
+ * last two octal-digits are tab width (we support only up to 63).
  */
-#define WS_BLANK_AT_EOL         0100
-#define WS_SPACE_BEFORE_TAB     0200
-#define WS_INDENT_WITH_NON_TAB  0400
-#define WS_CR_AT_EOL           01000
-#define WS_BLANK_AT_EOF        02000
-#define WS_TAB_IN_INDENT       04000
-#define WS_TRAILING_SPACE      (WS_BLANK_AT_EOL|WS_BLANK_AT_EOF)
+#define WS_BLANK_AT_EOL         (1<<6)
+#define WS_SPACE_BEFORE_TAB     (1<<7)
+#define WS_INDENT_WITH_NON_TAB  (1<<8)
+#define WS_CR_AT_EOL            (1<<9)
+#define WS_BLANK_AT_EOF         (1<<10)
+#define WS_TAB_IN_INDENT        (1<<11)
+
+#define WS_TRAILING_SPACE       (WS_BLANK_AT_EOL|WS_BLANK_AT_EOF)
 #define WS_DEFAULT_RULE (WS_TRAILING_SPACE|WS_SPACE_BEFORE_TAB|8)
-#define WS_TAB_WIDTH_MASK        077
-/* All WS_* -- when extended, adapt diff.c emit_symbol */
-#define WS_RULE_MASK           07777
+#define WS_TAB_WIDTH_MASK       ((1<<6)-1)
+
+/* All WS_* -- when extended, adapt constants defined after diff.c:diff_symbol */
+#define WS_RULE_MASK            ((1<<12)-1)
+
 extern unsigned whitespace_rule_cfg;
 unsigned whitespace_rule(struct index_state *, const char *);
 unsigned parse_whitespace_rule(const char *);