fixes for decimal type

mysql-test/r/type_newdecimal.result

@@ -1988,3 +1988,9 @@ SELECT d1 * d2 FROM t1;
 d1 * d2
 0
 DROP TABLE t1;
+select 0.000000000000000000000000000000000000000000000000001 mod 1;
+0.000000000000000000000000000000000000000000000000001 mod 1
+0.000000000000000000000000000000
+select 0.0000000001 mod 1;
+0.0000000001 mod 1
+0.0000000001

mysql-test/t/type_newdecimal.test

@@ -1570,3 +1570,12 @@ SELECT d1 * d2 FROM t1;
 
 DROP TABLE t1;
 
+#
+# Test for Bug#18469276: MOD FOR SMALL DECIMALS FAILS
+#
+select 0.000000000000000000000000000000000000000000000000001 mod 1;
+
+#
+# incorrect result
+#
+select 0.0000000001 mod 1;

strings/decimal.c

@@ -127,7 +127,6 @@ typedef longlong      dec2;
 #define DIG_BASE     1000000000
 #define DIG_MAX      (DIG_BASE-1)
 #define DIG_BASE2    ((dec2)DIG_BASE * (dec2)DIG_BASE)
-#define ROUND_UP(X)  (((X)+DIG_PER_DEC1-1)/DIG_PER_DEC1)
 static const dec1 powers10[DIG_PER_DEC1+1]={
   1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000};
 static const int dig2bytes[DIG_PER_DEC1+1]={0, 1, 1, 2, 2, 3, 3, 4, 4, 4};
@@ -136,6 +135,11 @@ static const dec1 frac_max[DIG_PER_DEC1-1]={
   999900000, 999990000, 999999000,
   999999900, 999999990 };
 
+static inline int ROUND_UP(int x)
+{
+  return (x + (x > 0 ? 1 : -1) * (DIG_PER_DEC1 - 1)) / DIG_PER_DEC1;
+}
+
 #ifdef HAVE_valgrind
 #define sanity(d) DBUG_ASSERT((d)->len > 0)
 #else