patch 7.4.848
Problem:    CTRL-A on hex number in Visual block mode is incorrect.
Solution:   Account for the "0x". (Hirohito Higashi)
diff --git a/src/charset.c b/src/charset.c
index 327fa03..a74bf0d 100644
--- a/src/charset.c
+++ b/src/charset.c
@@ -1909,6 +1909,8 @@
     else if (hex != 0 || dohex > 1)
     {
 	/* hex */
+	if (hex != 0)
+	    n += 2;	    /* skip over "0x" */
 	while (vim_isxdigit(*ptr))
 	{
 	    un = 16 * un + (unsigned long)hex2nr(*ptr);