3 files changed, 47 insertions, 16 deletions

diff --git a/mysql-test/r/func_math.result b/mysql-test/r/func_math.result
index fba274b9bb1..1507f959ae6 100644
--- a/mysql-test/r/func_math.result
+++ b/mysql-test/r/func_math.result
@@ -203,3 +203,18 @@ NULL
 Warnings:
 Error	1365	Division by 0
 set sql_mode='';
+select round(111,-10);
+round(111,-10)
+0
+select round(-5000111000111000155,-1);
+round(-5000111000111000155,-1)
+-5000111000111000160
+select round(15000111000111000155,-1);
+round(15000111000111000155,-1)
+15000111000111000160
+select truncate(-5000111000111000155,-1);
+truncate(-5000111000111000155,-1)
+-5000111000111000150
+select truncate(15000111000111000155,-1);
+truncate(15000111000111000155,-1)
+15000111000111000150
diff --git a/mysql-test/t/func_math.test b/mysql-test/t/func_math.test
index 9cf0ee452cd..8dc4eb215c7 100644
--- a/mysql-test/t/func_math.test
+++ b/mysql-test/t/func_math.test
@@ -141,3 +141,17 @@ select log(2,-1);
 select log(-2,1);
 set sql_mode='';
 
+#
+# Bug #8461 truncate() and round() return false results 2nd argument negative.
+# 
+# round(a,-b) log_10(b) > a
+select round(111,-10);
+# round on bigint 
+select round(-5000111000111000155,-1);
+# round on unsigned bigint
+select round(15000111000111000155,-1);
+# truncate on bigint 
+select truncate(-5000111000111000155,-1);
+# truncate on unsigned bigint
+select truncate(15000111000111000155,-1);
+
diff --git a/sql/item_func.cc b/sql/item_func.cc
index 2d595e5fdc8..a85f05c2e22 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -1863,28 +1863,30 @@ longlong Item_func_round::int_op()
     return value; // integer have not digits after point
 
   abs_dec= -dec;
-  double tmp;
-  /*
-    tmp2 is here to avoid return the value with 80 bit precision
-    This will fix that the test round(0.1,1) = round(0.1,1) is true
-  */
-  volatile double tmp2;
-
-  tmp= (abs_dec < array_elements(log_10) ?
-        log_10[abs_dec] : pow(10.0, (double) abs_dec));
-
+  longlong tmp;
+  
+  if(abs_dec >= array_elements(log_10_int))
+    return 0;
+  
+  tmp= log_10_int[abs_dec];
+  
   if (truncate)
   {
     if (unsigned_flag)
-      tmp2= floor(ulonglong2double(value)/tmp)*tmp;
-    else if (value >= 0)
-      tmp2= floor(((double)value)/tmp)*tmp;
+      value= (ulonglong(value)/tmp)*tmp;
     else
-      tmp2= ceil(((double)value)/tmp)*tmp;
+      value= (value/tmp)*tmp;
   }
   else
-    tmp2= rint(((double)value)/tmp)*tmp;
-  return (longlong)tmp2;
+  {
+    if (unsigned_flag)
+      value= ((ulonglong(value)+(tmp>>1))/tmp)*tmp;
+    else if ( value >= 0)
+      value= ((value+(tmp>>1))/tmp)*tmp;
+    else
+      value= ((value-(tmp>>1))/tmp)*tmp;
+  }
+  return value;
 }