diff --git a/README.md b/README.md
index b78d602..38ac06d 100644
--- a/README.md
+++ b/README.md
@@ -141,7 +141,8 @@ Use these commands to get version of interpreter:
    /  \/ / _` / __|/ _` | |
   / /\  / (_| \__ \ (_| | |
   \_\ \/ \__,_|___/\__,_|_|
-nasal interpreter ver 9.0
+nasal ver : 9.0
+c++ std   : 201103
 thanks to : https://github.com/andyross/nasal
 code repo : https://github.com/ValKmjolnir/Nasal-Interpreter
 code repo : https://gitee.com/valkmjolnir/Nasal-Interpreter
diff --git a/lib.nas b/lib.nas
index aae4964..e3d2476 100644
--- a/lib.nas
+++ b/lib.nas
@@ -363,6 +363,8 @@ var math=
     pi:    3.14159265358979323846264338327950288,
     inf:   1/0,
     nan:   0/0,
+    abs:   func(x)  {return x>0?x:-x;            },
+    floor: func(x)  {return __builtin_floor(x);  },
     pow:   func(x,y){return __builtin_pow(x,y);  },
     sin:   func(x)  {return __builtin_sin(x);    },
     cos:   func(x)  {return __builtin_cos(x);    },
diff --git a/main.cpp b/main.cpp
index 1b68716..03a705d 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,14 +1,14 @@
 #include "nasal.h"
 
-const uint32_t VM_LEXINFO  =1;
-const uint32_t VM_ASTINFO  =2;
-const uint32_t VM_CODEINFO =4;
-const uint32_t VM_EXECTIME =8;
-const uint32_t VM_OPCALLNUM=16;
-const uint32_t VM_EXEC     =32;
-const uint32_t VM_DBGINFO  =64;
-const uint32_t VM_DEBUG    =128;
-const uint32_t VM_OPTIMIZE =256;
+const uint32_t VM_LEXINFO  =0x01;
+const uint32_t VM_ASTINFO  =0x02;
+const uint32_t VM_CODEINFO =0x04;
+const uint32_t VM_EXECTIME =0x08;
+const uint32_t VM_OPCALLNUM=0x10;
+const uint32_t VM_EXEC     =0x20;
+const uint32_t VM_DBGINFO  =0x40;
+const uint32_t VM_DEBUG    =0x80;
+const uint32_t VM_OPTIMIZE =0x100;
 
 void help()
 {
@@ -43,10 +43,10 @@ void help()
 void logo()
 {
     std::cout
-    <<"       __                _      \n"
-    <<"    /\\ \\ \\__ _ ___  __ _| |  \n"
-    <<"   /  \\/ / _` / __|/ _` | |    \n"
-    <<"  / /\\  / (_| \\__ \\ (_| | |  \n"
+    <<"       __                _\n"
+    <<"    /\\ \\ \\__ _ ___  __ _| |\n"
+    <<"   /  \\/ / _` / __|/ _` | |\n"
+    <<"  / /\\  / (_| \\__ \\ (_| | |\n"
     <<"  \\_\\ \\/ \\__,_|___/\\__,_|_|\n"
     <<"nasal ver : "<<__nasver<<"\n"
     <<"c++ std   : "<<__cplusplus<<"\n"
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 22d5626..8440625 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -671,12 +671,14 @@ nasal_ref builtin_substr(nasal_ref* local,nasal_gc& gc)
         return builtin_err("substr","\"begin\" must be number");
     if(len.type!=vm_num)
         return builtin_err("substr","\"length\" must be number");
-    int begin=(int)beg.num();
-    int length=(int)len.num();
-    if(begin>=str.str().length() || begin+length-1>=str.str().length())
+    if(beg.num()<0)
+        return builtin_err("substr","\"begin\" should be greater than or equal to zero");
+    if(len.num()<0)
+        return builtin_err("substr","\"length\" should be greater than or equal to zero");
+    size_t begin=(size_t)beg.num();
+    size_t length=(size_t)len.num();
+    if(begin>=str.str().length() || begin+length>str.str().length())
         return builtin_err("susbtr","index out of range");
-    if(length<0)
-        length=0;
     nasal_ref ret=gc.alloc(vm_str);
     ret.str()=str.str().substr(begin,length);
     return ret;
diff --git a/nasal_vm.h b/nasal_vm.h
index 172e4d0..2cb5e2c 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -629,7 +629,7 @@ inline void nasal_vm::opr_counter()
 }
 inline void nasal_vm::opr_findex()
 {
-    if(++gc.top[0].cnt()>=gc.top[-1].vec().size())
+    if((size_t)(++gc.top[0].cnt())>=gc.top[-1].vec().size())
     {
         pc=imm[pc]-1;
         return;
@@ -640,7 +640,7 @@ inline void nasal_vm::opr_findex()
 inline void nasal_vm::opr_feach()
 {
     std::vector<nasal_ref>& ref=gc.top[-1].vec().elems;
-    if(++gc.top[0].cnt()>=ref.size())
+    if((size_t)(++gc.top[0].cnt())>=ref.size())
     {
         pc=imm[pc]-1;
         return;
diff --git a/stl/lib.nas b/stl/lib.nas
index aae4964..e3d2476 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -363,6 +363,8 @@ var math=
     pi:    3.14159265358979323846264338327950288,
     inf:   1/0,
     nan:   0/0,
+    abs:   func(x)  {return x>0?x:-x;            },
+    floor: func(x)  {return __builtin_floor(x);  },
     pow:   func(x,y){return __builtin_pow(x,y);  },
     sin:   func(x)  {return __builtin_sin(x);    },
     cos:   func(x)  {return __builtin_cos(x);    },
diff --git a/test/scalar.nas b/test/scalar.nas
index 49f46a8..3da440a 100644
--- a/test/scalar.nas
+++ b/test/scalar.nas
@@ -197,4 +197,7 @@ var a=[10,-10,0,1,2,3,nil,"string","hello",[],[0,1,2,3],{},{a:0,b:1,c:2},func{}]
 println("type\tsize\tnum\tsrc");
 foreach(var i;a){
     println(typeof(i),'\t',size(i),'\t',num(i),'\t',i);
+}
+foreach(i;a){
+    ;
 }
\ No newline at end of file