diff --git a/lib.nas b/lib.nas
index cad887a..696f3b1 100644
--- a/lib.nas
+++ b/lib.nas
@@ -267,6 +267,11 @@ var assert=func(condition,message="assertion failed!"){
     die(message);
 }
 
+# md5
+var md5=func(str){
+    return __builtin_md5(str);
+}
+
 var io=
 {
     SEEK_SET:0,
diff --git a/module/libmd5.nas b/module/libmd5.nas
deleted file mode 100644
index 8eb68bb..0000000
--- a/module/libmd5.nas
+++ /dev/null
@@ -1,10 +0,0 @@
-import("lib.nas");
-
-var md5=func(){
-    var lib=dylib.dlopen("./module/libmd5"~(os.platform()=="windows"?".dll":".so"));
-    var sym=dylib.dlsym(lib,"nas_md5");
-    var call=dylib.dlcall;
-    return func(s){
-        return call(sym,s);
-    };
-}();
\ No newline at end of file
diff --git a/module/makefile b/module/makefile
index a532c15..a61f2de 100644
--- a/module/makefile
+++ b/module/makefile
@@ -15,17 +15,9 @@ libkey.dll: keyboard.cpp
 	g++ -c -O3 keyboard.cpp -fPIC -o keyboard.o -static
 	g++ -shared -o libkey.dll keyboard.o -static
 
-libmd5.so: md5.cpp
-	clang++ -c -O3 md5.cpp -fPIC -o md5.o
-	clang++ -shared -o libmd5.so md5.o
-	rm md5.o
-libmd5.dll: md5.cpp
-	g++ -c -O3 md5.cpp -fPIC -o md5.o -static
-	g++ -shared -o libmd5.dll md5.o -static
-
 clean:
 	rm *.o *.so *.dll *.dylib
-all: libfib.so libkey.so libmd5.so
+all: libfib.so libkey.so
 	@ echo "build done"
-mingw-all: libfib.dll libkey.dll libmd5.dll
+mingw-all: libfib.dll libkey.dll
 	@ echo "build done"
\ No newline at end of file
diff --git a/module/md5.cpp b/module/md5.cpp
deleted file mode 100644
index 2998e6e..0000000
--- a/module/md5.cpp
+++ /dev/null
@@ -1,105 +0,0 @@
-#include "../nasal.h"
-
-uint32_t strlength;
-uint32_t* add(std::string str)
-{
-    uint32_t num=((str.length()+8)/64)+1;
-    uint32_t *strByte=new uint32_t[num*16];
-    strlength=num*16;
-    for (uint32_t i=0;i<num*16;i++)
-        strByte[i]=0;
-    for (uint32_t i=0;i<str.length();i++)
-        strByte[i>>2]|=(str[i])<<((i%4)*8);
-    strByte[str.length()>>2]|=0x80<<(((str.length()%4))*8);
-    strByte[num*16-2]=str.length()*8;
-    return strByte;
-}
-std::string changeHex(int a)
-{
-    const char str16[]="0123456789abcdef";
-    std::string str="";
-    for(int i=0;i<4;i++)
-    {
-        std::string str1="";
-        int b=((a>>i*8)%(1<<8))&0xff;
-        for (int j = 0; j < 2; j++)
-        {
-            str1.insert(0,1,str16[b%16]);
-            b=b/16;
-        }
-        str+=str1;
-    }
-    return str;
-}
-std::string md5(std::string source)
-{
-    // uint32_t(abs(sin(i+1))*(2pow32))
-    const uint32_t k[]={
-        0xd76aa478,0xe8c7b756,0x242070db,0xc1bdceee,0xf57c0faf,0x4787c62a,0xa8304613,0xfd469501,
-        0x698098d8,0x8b44f7af,0xffff5bb1,0x895cd7be,0x6b901122,0xfd987193,0xa679438e,0x49b40821,
-        0xf61e2562,0xc040b340,0x265e5a51,0xe9b6c7aa,0xd62f105d,0x02441453,0xd8a1e681,0xe7d3fbc8,
-        0x21e1cde6,0xc33707d6,0xf4d50d87,0x455a14ed,0xa9e3e905,0xfcefa3f8,0x676f02d9,0x8d2a4c8a,
-        0xfffa3942,0x8771f681,0x6d9d6122,0xfde5380c,0xa4beea44,0x4bdecfa9,0xf6bb4b60,0xbebfbc70,
-        0x289b7ec6,0xeaa127fa,0xd4ef3085,0x04881d05,0xd9d4d039,0xe6db99e5,0x1fa27cf8,0xc4ac5665,
-        0xf4292244,0x432aff97,0xab9423a7,0xfc93a039,0x655b59c3,0x8f0ccc92,0xffeff47d,0x85845dd1,
-        0x6fa87e4f,0xfe2ce6e0,0xa3014314,0x4e0811a1,0xf7537e82,0xbd3af235,0x2ad7d2bb,0xeb86d391
-    };
-    // left shift
-    const uint32_t s[]={
-        7,12,17,22,7,12,17,22,7,12,17,22,7,12,17,22,
-        5,9,14,20,5,9,14,20,5,9,14,20,5,9,14,20,
-        4,11,16,23,4,11,16,23,4,11,16,23,4,11,16,23,
-        6,10,15,21,6,10,15,21,6,10,15,21,6,10,15,21
-    };
-    // index
-    const uint32_t idx[]={
-        0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15, // g=i
-        1,6,11,0,5,10,15,4,9,14,3,8,13,2,7,12, // g=(5*i+1)%16;
-        5,8,11,14,1,4,7,10,13,0,3,6,9,12,15,2, // g=(3*i+5)%16;
-        0,7,14,5,12,3,10,1,8,15,6,13,4,11,2,9  // g=(7*i)%16;
-    };
-    uint32_t atmp=0x67452301,btmp=0xefcdab89;
-    uint32_t ctmp=0x98badcfe,dtmp=0x10325476;
-
-    uint32_t *strByte=add(source);
-#define shift(x,n) (((x)<<(n))|((x)>>(32-(n)))) // cycle left shift
-#define F(x,y,z) (((x)&(y))|((~x)&(z)))    
-#define G(x,y,z) (((x)&(z))|((y)&(~z)))
-#define H(x,y,z) ((x)^(y)^(z))
-#define I(x,y,z) ((y)^((x)|(~z)))
-    for(uint32_t i=0;i<strlength/16;i++)
-    {
-        uint32_t num[16];
-        for(uint32_t j=0;j<16;j++)
-            num[j]=strByte[i*16+j];
-        uint32_t f,g,a=atmp,b=btmp,c=ctmp,d=dtmp;
-        for(uint32_t i=0;i<64;i++)
-        {
-            if(i<16)      f=F(b,c,d);
-            else if(i<32) f=G(b,c,d);
-            else if(i<48) f=H(b,c,d);
-            else          f=I(b,c,d);
-            uint32_t tmp=d;
-            d=c;
-            c=b;
-            b=b+shift((a+f+k[i]+num[idx[i]]),s[i]);
-            a=tmp;
-        }
-        atmp+=a;
-        btmp+=b;
-        ctmp+=c;
-        dtmp+=d;
-    }
-    delete []strByte;
-    return changeHex(atmp).append(changeHex(btmp)).append(changeHex(ctmp)).append(changeHex(dtmp));
-}
-extern "C" nasal_ref nas_md5(std::vector<nasal_ref>& args,nasal_gc& gc){
-    if(!args.size())
-        return builtin_err("md5","lack arguments");
-    nasal_ref str=args[0];
-    if(str.type!=vm_str)
-        return builtin_err("md5","\"str\" must be a string");
-    nasal_ref res=gc.alloc(vm_str);
-    res.str()=md5(str.str());
-    return res;
-}
\ No newline at end of file
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 14829ef..f3b73b3 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -86,6 +86,7 @@ nas_native(builtin_dlclose);
 nas_native(builtin_dlcall);
 nas_native(builtin_platform);
 nas_native(builtin_gc);
+nas_native(builtin_md5);
 
 nasal_ref builtin_err(const char* func_name,std::string info)
 {
@@ -178,6 +179,7 @@ struct
     {"__builtin_dlcall",  builtin_dlcall  },
     {"__builtin_platform",builtin_platform},
     {"__builtin_gc",      builtin_gc      },
+    {"__builtin_md5",     builtin_md5     },
     {nullptr,             nullptr         }
 };
 
@@ -1222,4 +1224,98 @@ nasal_ref builtin_gc(nasal_ref* local,nasal_gc& gc)
     gc.sweep();
     return nil;
 }
+
+// md5 related functions
+std::string tohex(uint32_t num)
+{
+    const char str16[]="0123456789abcdef";
+    std::string str="";
+    for(uint32_t i=0;i<4;i++,num>>=8)
+    {
+        std::string tmp="";
+        for(uint32_t j=0,b=num&0xff;j<2;j++,b>>=4)
+            tmp.insert(0,1,str16[b&0xf]);
+        str+=tmp;
+    }
+    return str;
+}
+std::string md5(std::string& source)
+{
+    std::vector<uint32_t> buff;
+    uint32_t num=((source.length()+8)>>6)+1;
+    uint32_t buffsize=num<<4;
+    buff.resize(buffsize,0);
+    for(uint32_t i=0;i<source.length();i++)
+        buff[i>>2]|=(source[i])<<((i&0x3)<<3);
+    buff[source.length()>>2]|=0x80<<(((source.length()%4))<<3);
+    buff[buffsize-2]=(source.length()<<3)&0xffffffff;
+    buff[buffsize-1]=((source.length()<<3)>>32)&0xffffffff;
+
+    // uint32_t(abs(sin(i+1))*(2pow32))
+    const uint32_t k[]={
+        0xd76aa478,0xe8c7b756,0x242070db,0xc1bdceee,0xf57c0faf,0x4787c62a,0xa8304613,0xfd469501,
+        0x698098d8,0x8b44f7af,0xffff5bb1,0x895cd7be,0x6b901122,0xfd987193,0xa679438e,0x49b40821,
+        0xf61e2562,0xc040b340,0x265e5a51,0xe9b6c7aa,0xd62f105d,0x02441453,0xd8a1e681,0xe7d3fbc8,
+        0x21e1cde6,0xc33707d6,0xf4d50d87,0x455a14ed,0xa9e3e905,0xfcefa3f8,0x676f02d9,0x8d2a4c8a,
+        0xfffa3942,0x8771f681,0x6d9d6122,0xfde5380c,0xa4beea44,0x4bdecfa9,0xf6bb4b60,0xbebfbc70,
+        0x289b7ec6,0xeaa127fa,0xd4ef3085,0x04881d05,0xd9d4d039,0xe6db99e5,0x1fa27cf8,0xc4ac5665,
+        0xf4292244,0x432aff97,0xab9423a7,0xfc93a039,0x655b59c3,0x8f0ccc92,0xffeff47d,0x85845dd1,
+        0x6fa87e4f,0xfe2ce6e0,0xa3014314,0x4e0811a1,0xf7537e82,0xbd3af235,0x2ad7d2bb,0xeb86d391
+    };
+
+    // left shift bits
+    const uint32_t s[]={
+        7,12,17,22,7,12,17,22,7,12,17,22,7,12,17,22,
+        5,9,14,20,5,9,14,20,5,9,14,20,5,9,14,20,
+        4,11,16,23,4,11,16,23,4,11,16,23,4,11,16,23,
+        6,10,15,21,6,10,15,21,6,10,15,21,6,10,15,21
+    };
+
+    // index
+    const uint32_t idx[]={
+        0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15, // g=i
+        1,6,11,0,5,10,15,4,9,14,3,8,13,2,7,12, // g=(5*i+1)%16;
+        5,8,11,14,1,4,7,10,13,0,3,6,9,12,15,2, // g=(3*i+5)%16;
+        0,7,14,5,12,3,10,1,8,15,6,13,4,11,2,9  // g=(7*i)%16;
+    };
+    
+#define shift(x,n)  (((x)<<(n))|((x)>>(32-(n)))) // cycle left shift
+#define md5f(x,y,z) (((x)&(y))|((~x)&(z)))    
+#define md5g(x,y,z) (((x)&(z))|((y)&(~z)))
+#define md5h(x,y,z) ((x)^(y)^(z))
+#define md5i(x,y,z) ((y)^((x)|(~z)))
+    
+    uint32_t atmp=0x67452301,btmp=0xefcdab89;
+    uint32_t ctmp=0x98badcfe,dtmp=0x10325476;
+    for(uint32_t i=0;i<buffsize;i+=16)
+    {
+        uint32_t f,a=atmp,b=btmp,c=ctmp,d=dtmp;
+        for(uint32_t j=0;j<64;j++)
+        {
+            if(j<16)      f=md5f(b,c,d);
+            else if(j<32) f=md5g(b,c,d);
+            else if(j<48) f=md5h(b,c,d);
+            else          f=md5i(b,c,d);
+            uint32_t tmp=d;
+            d=c;
+            c=b;
+            b=b+shift((a+f+k[j]+buff[i+idx[j]]),s[j]);
+            a=tmp;
+        }
+        atmp+=a;
+        btmp+=b;
+        ctmp+=c;
+        dtmp+=d;
+    }
+    return tohex(atmp)+tohex(btmp)+tohex(ctmp)+tohex(dtmp);
+}
+nasal_ref builtin_md5(nasal_ref* local,nasal_gc& gc)
+{
+    nasal_ref str=local[1];
+    if(str.type!=vm_str)
+        return builtin_err("md5","\"str\" must be a string");
+    nasal_ref res=gc.alloc(vm_str);
+    res.str()=md5(str.str());
+    return res;
+}
 #endif
\ No newline at end of file
diff --git a/stl/lib.nas b/stl/lib.nas
index cad887a..696f3b1 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -267,6 +267,11 @@ var assert=func(condition,message="assertion failed!"){
     die(message);
 }
 
+# md5
+var md5=func(str){
+    return __builtin_md5(str);
+}
+
 var io=
 {
     SEEK_SET:0,
diff --git a/test/calc.nas b/test/calc.nas
index 1d83233..4fd2cfe 100644
--- a/test/calc.nas
+++ b/test/calc.nas
@@ -70,10 +70,8 @@ var testfile=[
 var module=[
     "module/fib.cpp        ",
     "module/keyboard.cpp   ",
-    "module/md5.cpp        ",
     "module/libfib.nas     ",
-    "module/libkey.nas     ",
-    "module/libmd5.nas     "
+    "module/libkey.nas     "
 ];
 
 var getname=func(s){
diff --git a/test/md5compare.nas b/test/md5compare.nas
index 4649954..a32288a 100644
--- a/test/md5compare.nas
+++ b/test/md5compare.nas
@@ -1,5 +1,4 @@
 import("lib.nas");
-import("module/libmd5.nas");
 import("test/md5.nas");
 
 rand(time(0));