diff --git a/lib.nas b/lib.nas
index 44c82b0..65a8882 100644
--- a/lib.nas
+++ b/lib.nas
@@ -60,6 +60,17 @@ var int=func(val){
     return __builtin_int(val);
 }
 
+# floor will get the integral number of input argument
+# which is less than or equal to this argument
+var floor=func(val){
+    return __builtin_floor(val);
+}
+
+# abs gets absolute number
+var abs=func(n){
+    return n>0?n:-n;
+}
+
 # num will change all the other types into number.
 # mostly used to change a numerable string.
 var num=func(val){
@@ -105,6 +116,9 @@ var keys=func(hash){
 var time=func(begin){
     return __builtin_time(begin);
 }
+var systime=func(){
+    return time(0);
+}
 
 # die is a special native function.
 # use it at where you want the program to crash immediately.
@@ -118,6 +132,11 @@ var typeof=func(object){
     return __builtin_type(object);
 }
 
+# subvec is used to get part of a vector
+var subvec=func(vec,begin,length=nil){
+    return vec[begin:(length==nil?nil:begin+length-1)];
+}
+
 # substr will get the sub-string.
 # it gets the string, the begin index and sub-string's length as arguments.
 var substr=func(str,begin,len){
@@ -169,6 +188,45 @@ var println=func(elems...){
     return __builtin_print(elems);
 }
 
+var isfunc=func(f){
+    return typeof(f)=="func";
+}
+
+var isghost=func(g){
+    die("this runtime have no ghost object");
+    return 0;
+}
+
+var ishash=func(h){
+    return typeof(h)=="hash";
+}
+
+var isint=func(x){
+    return x==floor(x);
+}
+
+var isnum=func(x){
+    return typeof(x)=="num" or !math.isnan(num(x));
+}
+
+var isscalar=func(s){
+    var t=typeof(s);
+    return t=="num" or t=="str";
+}
+
+var isstr=func(s){
+    return typeof(s)=="str";
+}
+
+var isvec=func(v){
+    return typeof(v)=="vec";
+}
+
+var vecindex=func(vec,val){
+    # unfinished
+    return nil;
+}
+
 var io=
 {
     SEEK_SET:0,
diff --git a/nasal_builtin.h b/nasal_builtin.h
index f932507..5d17c79 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -20,6 +20,7 @@ nas_native(builtin_split);
 nas_native(builtin_rand);
 nas_native(builtin_id);
 nas_native(builtin_int);
+nas_native(builtin_floor);
 nas_native(builtin_num);
 nas_native(builtin_pop);
 nas_native(builtin_str);
@@ -108,6 +109,7 @@ struct
     {"__builtin_rand",    builtin_rand    },
     {"__builtin_id",      builtin_id      },
     {"__builtin_int",     builtin_int     },
+    {"__builtin_floor",   builtin_floor   },
     {"__builtin_num",     builtin_num     },
     {"__builtin_pop",     builtin_pop     },
     {"__builtin_str",     builtin_str     },
@@ -363,6 +365,11 @@ nasal_ref builtin_int(nasal_ref* local,nasal_gc& gc)
     int number=(int)val.num();
     return {vm_num,(double)number};
 }
+nasal_ref builtin_floor(nasal_ref* local,nasal_gc& gc)
+{
+    nasal_ref val=local[1];
+    return {vm_num,std::floor(val.num())};
+}
 nasal_ref builtin_num(nasal_ref* local,nasal_gc& gc)
 {
     nasal_ref val=local[1];
diff --git a/nasal_vm.h b/nasal_vm.h
index 6952624..556c996 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -797,8 +797,8 @@ inline void nasal_vm::opr_slc2()
     else if(type1!=vm_nil && type2==vm_nil)
         num2=num1<0? -1:size-1;
 
-    if(num1>=num2)
-        die("slc2: begin index must be less than end index");
+    if(num1>num2)
+        die("slc2: begin index must be less than or equal to end index");
     else if(num1<-size || num1>=size)
         die("slc2: begin index out of range: "+std::to_string(num1));
     else if(num2<-size || num2>=size)
diff --git a/stl/lib.nas b/stl/lib.nas
index 44c82b0..65a8882 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -60,6 +60,17 @@ var int=func(val){
     return __builtin_int(val);
 }
 
+# floor will get the integral number of input argument
+# which is less than or equal to this argument
+var floor=func(val){
+    return __builtin_floor(val);
+}
+
+# abs gets absolute number
+var abs=func(n){
+    return n>0?n:-n;
+}
+
 # num will change all the other types into number.
 # mostly used to change a numerable string.
 var num=func(val){
@@ -105,6 +116,9 @@ var keys=func(hash){
 var time=func(begin){
     return __builtin_time(begin);
 }
+var systime=func(){
+    return time(0);
+}
 
 # die is a special native function.
 # use it at where you want the program to crash immediately.
@@ -118,6 +132,11 @@ var typeof=func(object){
     return __builtin_type(object);
 }
 
+# subvec is used to get part of a vector
+var subvec=func(vec,begin,length=nil){
+    return vec[begin:(length==nil?nil:begin+length-1)];
+}
+
 # substr will get the sub-string.
 # it gets the string, the begin index and sub-string's length as arguments.
 var substr=func(str,begin,len){
@@ -169,6 +188,45 @@ var println=func(elems...){
     return __builtin_print(elems);
 }
 
+var isfunc=func(f){
+    return typeof(f)=="func";
+}
+
+var isghost=func(g){
+    die("this runtime have no ghost object");
+    return 0;
+}
+
+var ishash=func(h){
+    return typeof(h)=="hash";
+}
+
+var isint=func(x){
+    return x==floor(x);
+}
+
+var isnum=func(x){
+    return typeof(x)=="num" or !math.isnan(num(x));
+}
+
+var isscalar=func(s){
+    var t=typeof(s);
+    return t=="num" or t=="str";
+}
+
+var isstr=func(s){
+    return typeof(s)=="str";
+}
+
+var isvec=func(v){
+    return typeof(v)=="vec";
+}
+
+var vecindex=func(vec,val){
+    # unfinished
+    return nil;
+}
+
 var io=
 {
     SEEK_SET:0,
diff --git a/test/md5.nas b/test/md5.nas
index 59db46f..08c63ea 100644
--- a/test/md5.nas
+++ b/test/md5.nas
@@ -3,15 +3,15 @@ import("lib.nas");
 var check=func(x){
     if(x<0x100000000)
         return x;
-    return x-int(x/0x100000000)*0x100000000;
+    return x-floor(x/0x100000000)*0x100000000;
 }
 var u32_bits_and=func(x,y){
     (x,y)=(check(x),check(y));
     var (res,op)=(0,1);
     for(var i=0;i<32;i+=1){
-        var (tmpx,tmpy)=(x-int(x/2)*2,y-int(y/2)*2);
+        var (tmpx,tmpy)=(x-floor(x/2)*2,y-floor(y/2)*2);
         res+=op*(tmpx==1 and tmpy==1);
-        (x,y)=(int(x/2),int(y/2));
+        (x,y)=(floor(x/2),floor(y/2));
         op*=2;
     }
     return res;
@@ -20,9 +20,9 @@ var u32_bits_or=func(x,y){
     (x,y)=(check(x),check(y));
     var (res,op)=(0,1);
     for(var i=0;i<32;i+=1){
-        var (tmpx,tmpy)=(x-int(x/2)*2,y-int(y/2)*2);
+        var (tmpx,tmpy)=(x-floor(x/2)*2,y-floor(y/2)*2);
         res+=op*(tmpx==1 or tmpy==1);
-        (x,y)=(int(x/2),int(y/2));
+        (x,y)=(floor(x/2),floor(y/2));
         op*=2;
     }
     return res;
@@ -31,9 +31,9 @@ var u32_bits_xor=func(x,y){
     (x,y)=(check(x),check(y));
     var (res,op)=(0,1);
     for(var i=0;i<32;i+=1){
-        var (tmpx,tmpy)=(x-int(x/2)*2,y-int(y/2)*2);
+        var (tmpx,tmpy)=(x-floor(x/2)*2,y-floor(y/2)*2);
         res+=op*(tmpx!=tmpy);
-        (x,y)=(int(x/2),int(y/2));
+        (x,y)=(floor(x/2),floor(y/2));
         op*=2;
     }
     return res;
@@ -42,8 +42,8 @@ var u32_bits_not=func(x){
     x=check(x);
     var (res,op)=(0,1);
     for(var i=0;i<32;i+=1){
-        res+=op*((x-int(x/2)*2)==1?0:1);
-        x=int(x/2);
+        res+=op*((x-floor(x/2)*2)==1?0:1);
+        x=floor(x/2);
         op*=2;
     }
     return res;
@@ -61,7 +61,7 @@ var hex32str=func(){
         var res="";
         for(var i=0;i<4;i+=1){
             res~=tbl[u32_bits_and(num,0xff)];
-            num=int(num/256);
+            num=floor(num/256);
         }
         return res;
     };
@@ -103,7 +103,7 @@ var _md5=func(){
         for(var i=0;i<cx;i+=1){
             num=num/2;
         }
-        return int(num);
+        return floor(num);
     }
     var rol=func(num,cx){
         return u32_bits_or(l(num,cx),r(num,32-cx));
@@ -141,72 +141,43 @@ var _md5=func(){
     ];
 
     return func(s){
-        var len=size(s)*8;
-        var res=[];
-        setsize(res,len);
-        for(var i=0;i<size(s);i+=1){
-            var c=s[i];
-            var v=128;
-            for(var j=0;j<8;j+=1){
-                res[i*8+j]=(bits.bitand(c,v)?1:0);
-                v=int(v/2);
-            }
+        var (s_size,len,res)=(size(s),size(s)*8,[]);
+        setsize(res,s_size);
+        for(var i=0;i<s_size;i+=1){
+            res[i]=s[i];
         }
         # +------len------+--1~512--+--64--+
         # |      text     |  fill   | size |
-        # +---------------+---------+------+ N*512
-        var mod=size(res)-int(size(res)/512)*512;
-        if(mod==448){
-            var i=size(res);
-            setsize(res,i+512);
-            res[i]=1;
-            for(i+=1;i<size(res);i+=1)
-                res[i]=0;
-        }elsif(mod<448){
-            var i=size(res);
-            setsize(res,int(i/512)*512+448);
-            res[i]=1;
-            for(i+=1;i<size(res);i+=1)
-                res[i]=0;
-        }elsif(mod>448){
-            var i=size(res);
-            setsize(res,int(i/512)*512+960); # 512+448=960
-            res[i]=1;
-            for(i+=1;i<size(res);i+=1)
-                res[i]=0;
+        # +---------------+---------+------+ N*512 bit
+        var (mod,res_size)=(s_size-floor(s_size/64)*64,0);
+        if(mod==56){
+            res_size=s_size+64;
+        }elsif(mod<56){
+            res_size=floor(s_size/64)*64+56;
+        }elsif(mod>56){
+            res_size=floor(s_size/64)*64+120; # 512+448=960 960/8=120
         }
+        setsize(res,res_size);
+        res[s_size]=0x80;
+        for(var i=s_size+1;i<res_size;i+=1)
+            res[i]=0;
 
-        # translate bits to bytes and reserve 64bit space for string length
-        var (tmp,cnt,t,index)=([],0,0,0);
-        setsize(tmp,int(size(res)/8)+8);
-        foreach(var i;res){
-            if(!cnt) t=i;
-            else     t=t*2+i;
-            cnt+=1;
-            if(cnt==8){
-                tmp[index]=t;
-                index+=1;
-                cnt=0;
-            }
-        }
-
-        # little endian, this may have number overflow bug
-        # if the number is too large
-        var (tmp_size,lower32,higher32)=(size(tmp),check(len),check(len/math.pow(2,32)));
+        # little endian
+        setsize(res,size(res)+8);
+        var (s_size,lower32,higher32)=(size(res),check(len),check(len/math.pow(2,32)));
         for(var i=4;i>0;i-=1){
-            tmp[tmp_size-4-i]=int(lower32-int(lower32/256)*256);
-            lower32=int(lower32/256);
+            res[s_size-4-i]=floor(lower32-floor(lower32/256)*256);
+            lower32=floor(lower32/256);
         }
         for(var i=4;i>0;i-=1){
-            tmp[tmp_size-i]=int(higher32-int(higher32/256)*256);
-            higher32=int(higher32/256);
+            res[s_size-i]=floor(higher32-floor(higher32/256)*256);
+            higher32=floor(higher32/256);
         }
-        res=tmp;
 
         # 1 block=>16 uint32=>64 byte=>512 bit
         # because using double to discribe number
         # this may only work when string's length is under 1<<51
-        tmp=[];
+        var tmp=[];
         setsize(tmp,size(res)/4);
         for(var i=0;i<size(res);i+=4){
             tmp[i/4]=res[i+3]*math.pow(2,24)+