diff --git a/nasal_codegen.h b/nasal_codegen.h
index c00571c..1683888 100644
--- a/nasal_codegen.h
+++ b/nasal_codegen.h
@@ -1272,7 +1272,10 @@ void nasal_codegen::print_op(uint32_t index)
             std::cout<<num_res[c.num&0x7fffffff]<<") sp-"<<(c.num>>31)<<"\n";
             break;
         case op_lnkeqc:
-            printf("0x%x (\"%s\") sp-%u\n",c.num&0x7fffffff,rawstr(str_res[c.num&0x7fffffff]).c_str(),c.num>>31);break;
+        {
+            std::string tmp=rawstr(str_res[c.num&0x7fffffff]);
+            printf("0x%x (\"%.16s%s\") sp-%u\n",c.num&0x7fffffff,tmp.c_str(),tmp.length()>16?"...":"",c.num>>31);
+        }break;
         case op_addc:  case op_subc:   case op_mulc:  case op_divc:
         case op_lessc: case op_leqc:   case op_grtc:  case op_geqc:
         case op_pnum:
@@ -1291,7 +1294,10 @@ void nasal_codegen::print_op(uint32_t index)
         case op_lnkc:
         case op_callh: case op_mcallh:
         case op_para:  case op_defpara:case op_dynpara:
-            printf("0x%x (\"%s\")\n",c.num,rawstr(str_res[c.num]).c_str());break;
+        {
+            std::string tmp=rawstr(str_res[c.num]);
+            printf("0x%x (\"%.16s%s\")\n",c.num,tmp.c_str(),tmp.length()>16?"...":"");
+        }break;
         default:printf("\n");break;
     }
 }
diff --git a/nasal_gc.h b/nasal_gc.h
index 97f0c90..4196e9e 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -22,7 +22,7 @@ enum nasal_type
 
 // change parameters here to make your own efficient gc
 // better set bigger number on vm_vec
-const uint32_t increment[vm_type_size]=
+const uint32_t initialize[vm_type_size]=
 {
     /* none-gc object */
     0,   // vm_none, error type
@@ -39,6 +39,23 @@ const uint32_t increment[vm_type_size]=
     512, // vm_upval
     16   // vm_obj
 };
+const uint32_t increment[vm_type_size]=
+{
+    /* none-gc object */
+    0,   // vm_none, error type
+    0,   // vm_count, used in foreach/forindex
+    0,   // vm_addr, used to store local address pointers
+    0,   // vm_ret, used to store call-return address
+    0,   // vm_nil
+    0,   // vm_num
+    /* gc object */
+    1024,// vm_str
+    512, // vm_func
+    8192,// vm_vec
+    1024,// vm_hash
+    128, // vm_upval
+    256  // vm_obj
+};
 
 struct nasal_vec;  // vector
 struct nasal_hash; // hashmap(dict)
@@ -468,7 +485,7 @@ void nasal_gc::init(const std::vector<std::string>& s)
     for(uint8_t i=0;i<vm_type_size;++i)
         size[i]=count[i]=0;
     for(uint8_t i=vm_str;i<vm_type_size;++i)
-        for(uint32_t j=0;j<increment[i];++j)
+        for(uint32_t j=0;j<initialize[i];++j)
         {
             nasal_val* tmp=new nasal_val(i);
             memory.push_back(tmp);
@@ -510,7 +527,7 @@ void nasal_gc::info()
         std::cout<<"  "<<name[i]<<" | "<<count[i]<<"\n";
     std::cout<<"\nmemory allocator info(max size):\n";
     for(uint8_t i=vm_str;i<vm_type_size;++i)
-        std::cout<<"  "<<name[i]<<" | "<<(size[i]+1)*increment[i]<<"(+"<<size[i]<<")\n";
+        std::cout<<"  "<<name[i]<<" | "<<initialize[i]+size[i]*increment[i]<<"(+"<<size[i]<<")\n";
 }
 nasal_ref nasal_gc::alloc(uint8_t type)
 {
diff --git a/nasal_vm.h b/nasal_vm.h
index b82dc80..172e4d0 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -152,7 +152,11 @@ void nasal_vm::valinfo(nasal_ref& val)
         case vm_cnt:  printf("| cnt  | %ld\n",val.cnt());break;
         case vm_nil:  printf("| nil  |\n");break;
         case vm_num:  printf("| num  | ");std::cout<<val.num()<<'\n';break;
-        case vm_str:  printf("| str  | <0x%lx> %s\n",(uint64_t)p,rawstr(val.str()).c_str());break;
+        case vm_str:
+        {
+            std::string tmp=rawstr(val.str());
+            printf("| str  | <0x%lx> %.16s%s\n",(uint64_t)p,tmp.c_str(),tmp.length()>16?"...":"");
+        }break;
         case vm_func: printf("| func | <0x%lx> entry:0x%x\n",(uint64_t)p,val.func().entry);break;
         case vm_vec:  printf("| vec  | <0x%lx> [%lu val]\n",(uint64_t)p,val.vec().size());break;
         case vm_hash: printf("| hash | <0x%lx> {%lu val}\n",(uint64_t)p,val.hash().size());break;
@@ -183,7 +187,10 @@ void nasal_vm::bytecodeinfo(const char* header,const uint32_t p)
             std::cout<<num_table[c.num&0x7fffffff]<<") sp-"<<(c.num>>31);
             break;
         case op_lnkeqc:
-            printf("0x%x (\"%s\") sp-%u",c.num&0x7fffffff,rawstr(str_table[c.num&0x7fffffff]).c_str(),c.num>>31);break;
+        {
+            std::string tmp=rawstr(str_table[c.num&0x7fffffff]);
+            printf("0x%x (\"%.16s%s\") sp-%u",c.num&0x7fffffff,tmp.c_str(),tmp.length()>16?"...":"",c.num>>31);
+        }break;
         case op_addc:  case op_subc:   case op_mulc:  case op_divc:
         case op_lessc: case op_leqc:   case op_grtc:  case op_geqc:
         case op_pnum:
@@ -202,7 +209,10 @@ void nasal_vm::bytecodeinfo(const char* header,const uint32_t p)
         case op_lnkc:
         case op_callh: case op_mcallh:
         case op_para:  case op_defpara:case op_dynpara:
-            printf("0x%x (\"%s\")",c.num,rawstr(str_table[c.num]).c_str());break;
+        {
+            std::string tmp=rawstr(str_table[c.num]);
+            printf("0x%x (\"%.16s%s\")",c.num,tmp.c_str(),tmp.length()>16?"...":"");
+        }break;
         default:printf("0x%x",c.num);break;
     }
     printf(" (%s:%d)\n",files[c.fidx].c_str(),c.line);
diff --git a/test/diff.nas b/test/diff.nas
index f13ae3f..64f3c3a 100644
--- a/test/diff.nas
+++ b/test/diff.nas
@@ -5,27 +5,19 @@ var myers=func(src,dst,show_table=0){
     var (src_len,dst_len)=(size(src),size(dst));
 
     var mat=[];
-    setsize(mat,dst_len);
+    setsize(mat,dst_len*src_len);
     forindex(var i;mat){
-        var tmp=[];
-        setsize(tmp,src_len);
-        mat[i]=tmp;
-        forindex(var j;tmp)
-            tmp[j]=0;
+        mat[i]=0;
     }
     var visited=[];
-    setsize(visited,dst_len);
+    setsize(visited,dst_len*src_len);
     forindex(var i;visited){
-        var tmp=[];
-        setsize(tmp,src_len);
-        visited[i]=tmp;
-        forindex(var j;tmp)
-            tmp[j]=0;
+        visited[i]=0;
     }
 
     forindex(var y;dst)
         forindex(var x;src)
-            mat[y][x]=(src[x]==dst[y]);
+            mat[y*src_len+x]=(src[x]==dst[y]);
 
     if(show_table){
         var curve=[
@@ -39,7 +31,7 @@ var myers=func(src,dst,show_table=0){
         forindex(var y;dst){
             forindex(var t;curve[0]){
                 forindex(var x;src){
-                    s~=curve[mat[y][x]][t];
+                    s~=curve[mat[y*src_len+x]][t];
                 }
                 s~=["+","|"][t]~"\n";
             }
@@ -52,7 +44,7 @@ var myers=func(src,dst,show_table=0){
     var total=[];
     var path=[];
     var vec=[[0,0,-1]];
-    visited[0][0]=1;
+    visited[0]=1;
     while(size(vec)){
         append(total,vec);
         var tmp=[];
@@ -96,20 +88,20 @@ var myers=func(src,dst,show_table=0){
             }
 
             # do bfs
-            if(mat[y][x]==1){
-                if(x+1<src_len and y+1<dst_len and visited[y+1][x+1]==0){
+            if(mat[y*src_len+x]==1){
+                if(x+1<src_len and y+1<dst_len and visited[(y+1)*src_len+x+1]==0){
                     append(tmp,[y+1,x+1,i]);
-                    visited[y+1][x+1]=1;
+                    visited[(y+1)*src_len+x+1]=1;
                 }
             }
             else{
-                if(x+1<src_len and visited[y][x+1]==0){
+                if(x+1<src_len and visited[y*src_len+x+1]==0){
                     append(tmp,[y,x+1,i]);
-                    visited[y][x+1]=1;
+                    visited[y*src_len+x+1]=1;
                 }
-                if(y+1<dst_len and visited[y+1][x]==0){
+                if(y+1<dst_len and visited[(y+1)*src_len+x]==0){
                     append(tmp,[y+1,x,i]);
-                    visited[y+1][x]=1;
+                    visited[(y+1)*src_len+x]=1;
                 }
             }
         }