lib/vsprintf.c: "%#o",0 becomes '0' instead of '00'

number()'s behaviour is slighly changed: 0 becomes "0" instead of "00"
when using the flag SPECIAL and base 8.

Before:
Number\Format  %o    %#o  %x    %#x
            0     0   00    0   0x0
            1     1   01    1   0x1
           16    20  020   10  0x10

After:
Number\Format  %o    %#o  %x    %#x
            0     0    0    0   0x0
            1     1   01    1   0x1
           16    20  020   10  0x10

Signed-off-by: Pierre Carrier <pierre@spotify.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/vsprintf.c

@@ -284,6 +284,7 @@ char *number(char *buf, char *end, unsigned long long num,
 	char locase;
 	int need_pfx = ((spec.flags & SPECIAL) && spec.base != 10);
 	int i;
+	bool is_zero = num == 0LL;
 
 	/* locase = 0 or 0x20. ORing digits or letters with 'locase'
 	 * produces same digits or (maybe lowercased) letters */
@@ -305,8 +306,9 @@ char *number(char *buf, char *end, unsigned long long num,
 		}
 	}
 	if (need_pfx) {
-		spec.field_width--;
 		if (spec.base == 16)
+			spec.field_width -= 2;
+		else if (!is_zero)
 			spec.field_width--;
 	}
 
@@ -353,9 +355,11 @@ char *number(char *buf, char *end, unsigned long long num,
 	}
 	/* "0x" / "0" prefix */
 	if (need_pfx) {
-		if (buf < end)
-			*buf = '0';
-		++buf;
+		if (spec.base == 16 || !is_zero) {
+			if (buf < end)
+				*buf = '0';
+			++buf;
+		}
 		if (spec.base == 16) {
 			if (buf < end)
 				*buf = ('X' | locase);