time: drop dead code from gmtime()

"days", as calculated, can't be negative. Drop the respective loop and
change its type. Similarly "rem" can't be negative and doesn't require
more than 32 bits. Change its type, too.

As a consequence, the tm_wday calculation also can't yield negative
values, so the respective conditional can be dropped as well.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/common/time.c

@@ -45,7 +45,8 @@ static DEFINE_SPINLOCK(wc_lock);
 struct tm gmtime(unsigned long t)
 {
     struct tm tbuf;
-    long days, rem;
+    unsigned long days;
+    unsigned int rem;
     int y;
     const unsigned short int *ip;
 
@@ -70,18 +71,11 @@ struct tm gmtime(unsigned long t)
     tbuf.tm_sec = rem % 60;
     /* January 1, 1970 was a Thursday.  */
     tbuf.tm_wday = (4 + days) % 7;
-    if ( tbuf.tm_wday < 0 )
-        tbuf.tm_wday += 7;
     while ( days >= (rem = __isleap(y) ? 366 : 365) )
     {
         ++y;
         days -= rem;
     }
-    while ( days < 0 )
-    {
-        --y;
-        days += __isleap(y) ? 366 : 365;
-    }
     tbuf.tm_year = y - 1900;
     tbuf.tm_yday = days;
     /* SAF-14-safe use boolean as an array index */