diff --git a/CMakeLists.txt b/CMakeLists.txt
index b86c9bf..8dbdfd5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -22,6 +22,7 @@ set(NASAL_OBJECT_SOURCE_FILE
     ${CMAKE_SOURCE_DIR}/src/nasal_builtin.cpp
     ${CMAKE_SOURCE_DIR}/src/coroutine.cpp
     ${CMAKE_SOURCE_DIR}/src/fg_props.cpp
+    ${CMAKE_SOURCE_DIR}/src/bits_lib.cpp
     ${CMAKE_SOURCE_DIR}/src/math_lib.cpp
     ${CMAKE_SOURCE_DIR}/src/nasal_codegen.cpp
     ${CMAKE_SOURCE_DIR}/src/nasal_dbg.cpp
diff --git a/makefile b/makefile
index 713cd42..0276c49 100644
--- a/makefile
+++ b/makefile
@@ -18,6 +18,7 @@ NASAL_HEADER=\
 	src/optimizer.h\
 	src/symbol_finder.h\
 	src/fg_props.h\
+	src/bits_lib.h\
 	src/math_lib.h\
 	src/coroutine.h
 
@@ -25,6 +26,7 @@ NASAL_OBJECT=\
 	build/nasal_err.o\
 	build/nasal_ast.o\
 	build/ast_visitor.o\
+	build/bits_lib.o\
 	build/ast_dumper.o\
 	build/nasal_lexer.o\
 	build/nasal_parse.o\
@@ -97,6 +99,12 @@ build/coroutine.o: \
 	src/coroutine.h src/coroutine.cpp | build
 	$(CXX) -std=$(STD) -c -O3 src/coroutine.cpp -fno-exceptions -fPIC -o build/coroutine.o -I .
 
+build/bits_lib.o: \
+	src/nasal.h\
+	src/nasal_gc.h\
+	src/bits_lib.h src/bits_lib.cpp | build
+	$(CXX) -std=$(STD) -c -O3 src/bits_lib.cpp -fno-exceptions -fPIC -o build/bits_lib.o -I .
+
 build/math_lib.o: \
 	src/nasal.h\
 	src/nasal_gc.h\
diff --git a/src/bits_lib.cpp b/src/bits_lib.cpp
new file mode 100644
index 0000000..67cdf1d
--- /dev/null
+++ b/src/bits_lib.cpp
@@ -0,0 +1,137 @@
+#include "bits_lib.h"
+
+var builtin_u32xor(var* local, gc& ngc) {
+    return var::num((f64)(u32(local[1].num())^u32(local[2].num())));
+}
+
+var builtin_u32and(var* local, gc& ngc) {
+    return var::num((f64)(u32(local[1].num())&u32(local[2].num())));
+}
+
+var builtin_u32or(var* local, gc& ngc) {
+    return var::num((f64)(u32(local[1].num())|u32(local[2].num())));
+}
+
+var builtin_u32nand(var* local, gc& ngc) {
+    return var::num((f64)(u32)(~(u32(local[1].num())&u32(local[2].num()))));
+}
+
+var builtin_u32not(var* local, gc& ngc) {
+    return var::num((f64)(u32)(~u32(local[1].num())));
+}
+
+var builtin_fld(var* local, gc& ngc) {
+    // bits.fld(s,0,3);
+    // if s stores 10100010(162)
+    // will get 101(5)
+    var str = local[1];
+    var startbit = local[2];
+    var length = local[3];
+    if (str.type!=vm_str || str.val.gcobj->unmut) {
+        return nas_err("fld", "\"str\" must be mutable string");
+    }
+    if (startbit.type!=vm_num || length.type!=vm_num) {
+        return nas_err("fld", "\"startbit\",\"len\" must be number");
+    }
+    u32 bit = (u32)startbit.num();
+    u32 len = (u32)length.num();
+    if (bit+len>8*str.str().length()) {
+        return nas_err("fld", "bitfield out of bounds");
+    }
+    u32 res = 0;
+    auto& s = str.str();
+    for(u32 i = bit; i<bit+len; ++i) {
+        if (s[i>>3]&(1<<(7-(i&7)))) {
+            res |= 1<<(bit+len-i-1);
+        }
+    }
+    return var::num((f64)res);
+}
+
+var builtin_sfld(var* local, gc& ngc) {
+    // bits.sfld(s,0,3);
+    // if s stores 10100010(162)
+    // will get 101(5) then this will be signed extended to
+    // 11111101(-3)
+    var str = local[1];
+    var startbit = local[2];
+    var length = local[3];
+    if (str.type!=vm_str || str.val.gcobj->unmut) {
+        return nas_err("sfld", "\"str\" must be mutable string");
+    }
+    if (startbit.type!=vm_num || length.type!=vm_num) {
+        return nas_err("sfld", "\"startbit\",\"len\" must be number");
+    }
+    u32 bit = (u32)startbit.num();
+    u32 len = (u32)length.num();
+    if (bit+len>8*str.str().length()) {
+        return nas_err("sfld", "bitfield out of bounds");
+    }
+    u32 res = 0;
+    auto& s = str.str();
+    for(u32 i = bit; i<bit+len; ++i) {
+        if (s[i>>3]&(1<<(7-(i&7)))) {
+            res |= 1<<(bit+len-i-1);
+        }
+    }
+    if (res&(1<<(len-1))) {
+        res |= ~((1<<len)-1);
+    }
+    return var::num((f64)((i32)res));
+}
+
+var builtin_setfld(var* local, gc& ngc) {
+    // bits.setfld(s,0,8,69);
+    // set 01000101(69) to string will get this:
+    // 10100010(162)
+    // so s[0]=162
+    var str = local[1];
+    var startbit = local[2];
+    var length = local[3];
+    var value = local[4];
+    if (str.type!=vm_str || str.val.gcobj->unmut) {
+        return nas_err("setfld", "\"str\" must be mutable string");
+    }
+    if (startbit.type!=vm_num || length.type!=vm_num || value.type!=vm_num) {
+        return nas_err("setfld", "\"startbit\",\"len\",\"val\" must be number");
+    }
+    u32 bit = (u32)startbit.num();
+    u32 len = (u32)length.num();
+    u64 val = (u64)value.num();
+    if (bit+len>8*str.str().length()) {
+        return nas_err("setfld", "bitfield out of bounds");
+    }
+    auto& s = str.str();
+    for(u32 i = bit; i<bit+len; ++i) {
+        if (val&(1<<(i-bit))) {
+            s[i>>3] |= (1<<(7-(i&7)));
+        } else {
+            s[i>>3] &= ~(1<<(7-(i&7)));
+        }
+    }
+    return nil;
+}
+
+var builtin_buf(var* local, gc& ngc) {
+    var length = local[1];
+    if (length.type!=vm_num || length.num()<=0) {
+        return nas_err("buf", "\"len\" must be number greater than 0");
+    }
+    var str = ngc.alloc(vm_str);
+    auto& s = str.str();
+    s.resize(length.num(), '\0');
+    return str;
+}
+
+nasal_builtin_table bits_native[] = {
+    {"__u32xor", builtin_u32xor},
+    {"__u32and", builtin_u32and},
+    {"__u32or", builtin_u32or},
+    {"__u32nand", builtin_u32nand},
+    {"__u32not", builtin_u32not},
+    {"__fld", builtin_fld},
+    {"__sfld", builtin_sfld},
+    {"__setfld", builtin_setfld},
+    {"__buf", builtin_buf},
+    {nullptr, nullptr}
+};
\ No newline at end of file
diff --git a/src/bits_lib.h b/src/bits_lib.h
new file mode 100644
index 0000000..72fbca9
--- /dev/null
+++ b/src/bits_lib.h
@@ -0,0 +1,17 @@
+#pragma once
+
+#include "nasal.h"
+#include "nasal_gc.h"
+#include "nasal_builtin.h"
+
+var builtin_u32xor(var*, gc&);
+var builtin_u32and(var*, gc&);
+var builtin_u32or(var*, gc&);
+var builtin_u32nand(var*, gc&);
+var builtin_u32not(var*, gc&);
+var builtin_fld(var*, gc&);
+var builtin_sfld(var*, gc&);
+var builtin_setfld(var*, gc&);
+var builtin_buf(var*, gc&);
+
+extern nasal_builtin_table bits_native[];
diff --git a/src/nasal_builtin.cpp b/src/nasal_builtin.cpp
index c42f94d..60ec19e 100644
--- a/src/nasal_builtin.cpp
+++ b/src/nasal_builtin.cpp
@@ -223,26 +223,6 @@ var builtin_size(var* local, gc& ngc) {
     return var::num(num);
 }
 
-var builtin_u32xor(var* local, gc& ngc) {
-    return var::num((f64)(u32(local[1].num())^u32(local[2].num())));
-}
-
-var builtin_u32and(var* local, gc& ngc) {
-    return var::num((f64)(u32(local[1].num())&u32(local[2].num())));
-}
-
-var builtin_u32or(var* local, gc& ngc) {
-    return var::num((f64)(u32(local[1].num())|u32(local[2].num())));
-}
-
-var builtin_u32nand(var* local, gc& ngc) {
-    return var::num((f64)(u32)(~(u32(local[1].num())&u32(local[2].num()))));
-}
-
-var builtin_u32not(var* local, gc& ngc) {
-    return var::num((f64)(u32)(~u32(local[1].num())));
-}
-
 var builtin_time(var* local, gc& ngc) {
     var val = local[1];
     if (val.type!=vm_num) {
@@ -590,109 +570,6 @@ var builtin_eof(var* local, gc& ngc) {
     return var::num((f64)feof((FILE*)fd.obj().ptr));
 }
 
-var builtin_fld(var* local, gc& ngc) {
-    // bits.fld(s,0,3);
-    // if s stores 10100010(162)
-    // will get 101(5)
-    var str = local[1];
-    var startbit = local[2];
-    var length = local[3];
-    if (str.type!=vm_str || str.val.gcobj->unmut) {
-        return nas_err("fld", "\"str\" must be mutable string");
-    }
-    if (startbit.type!=vm_num || length.type!=vm_num) {
-        return nas_err("fld", "\"startbit\",\"len\" must be number");
-    }
-    u32 bit = (u32)startbit.num();
-    u32 len = (u32)length.num();
-    if (bit+len>8*str.str().length()) {
-        return nas_err("fld", "bitfield out of bounds");
-    }
-    u32 res = 0;
-    auto& s = str.str();
-    for(u32 i = bit; i<bit+len; ++i) {
-        if (s[i>>3]&(1<<(7-(i&7)))) {
-            res |= 1<<(bit+len-i-1);
-        }
-    }
-    return var::num((f64)res);
-}
-
-var builtin_sfld(var* local, gc& ngc) {
-    // bits.sfld(s,0,3);
-    // if s stores 10100010(162)
-    // will get 101(5) then this will be signed extended to
-    // 11111101(-3)
-    var str = local[1];
-    var startbit = local[2];
-    var length = local[3];
-    if (str.type!=vm_str || str.val.gcobj->unmut) {
-        return nas_err("sfld", "\"str\" must be mutable string");
-    }
-    if (startbit.type!=vm_num || length.type!=vm_num) {
-        return nas_err("sfld", "\"startbit\",\"len\" must be number");
-    }
-    u32 bit = (u32)startbit.num();
-    u32 len = (u32)length.num();
-    if (bit+len>8*str.str().length()) {
-        return nas_err("sfld", "bitfield out of bounds");
-    }
-    u32 res = 0;
-    auto& s = str.str();
-    for(u32 i = bit; i<bit+len; ++i) {
-        if (s[i>>3]&(1<<(7-(i&7)))) {
-            res |= 1<<(bit+len-i-1);
-        }
-    }
-    if (res&(1<<(len-1))) {
-        res |= ~((1<<len)-1);
-    }
-    return var::num((f64)((i32)res));
-}
-
-var builtin_setfld(var* local, gc& ngc) {
-    // bits.setfld(s,0,8,69);
-    // set 01000101(69) to string will get this:
-    // 10100010(162)
-    // so s[0]=162
-    var str = local[1];
-    var startbit = local[2];
-    var length = local[3];
-    var value = local[4];
-    if (str.type!=vm_str || str.val.gcobj->unmut) {
-        return nas_err("setfld", "\"str\" must be mutable string");
-    }
-    if (startbit.type!=vm_num || length.type!=vm_num || value.type!=vm_num) {
-        return nas_err("setfld", "\"startbit\",\"len\",\"val\" must be number");
-    }
-    u32 bit = (u32)startbit.num();
-    u32 len = (u32)length.num();
-    u64 val = (u64)value.num();
-    if (bit+len>8*str.str().length()) {
-        return nas_err("setfld", "bitfield out of bounds");
-    }
-    auto& s = str.str();
-    for(u32 i = bit; i<bit+len; ++i) {
-        if (val&(1<<(i-bit))) {
-            s[i>>3] |= (1<<(7-(i&7)));
-        } else {
-            s[i>>3] &= ~(1<<(7-(i&7)));
-        }
-    }
-    return nil;
-}
-
-var builtin_buf(var* local, gc& ngc) {
-    var length = local[1];
-    if (length.type!=vm_num || length.num()<=0) {
-        return nas_err("buf", "\"len\" must be number greater than 0");
-    }
-    var str = ngc.alloc(vm_str);
-    auto& s = str.str();
-    s.resize(length.num(), '\0');
-    return str;
-}
-
 var builtin_sleep(var* local, gc& ngc) {
     var val = local[1];
     if (val.type!=vm_num) {
@@ -1137,11 +1014,6 @@ nasal_builtin_table builtin[] = {
     {"__pop", builtin_pop},
     {"__str", builtin_str},
     {"__size", builtin_size},
-    {"__u32xor", builtin_u32xor},
-    {"__u32and", builtin_u32and},
-    {"__u32or", builtin_u32or},
-    {"__u32nand", builtin_u32nand},
-    {"__u32not", builtin_u32not},
     {"__time", builtin_time},
     {"__contains", builtin_contains},
     {"__delete", builtin_delete},
@@ -1167,10 +1039,6 @@ nasal_builtin_table builtin[] = {
     {"__readln", builtin_readln},
     {"__stat", builtin_stat},
     {"__eof", builtin_eof},
-    {"__fld", builtin_fld},
-    {"__sfld", builtin_sfld},
-    {"__setfld", builtin_setfld},
-    {"__buf", builtin_buf},
     {"__sleep", builtin_sleep},
     {"__pipe", builtin_pipe},
     {"__fork", builtin_fork},
diff --git a/src/nasal_builtin.h b/src/nasal_builtin.h
index 5c62658..f4a4e3d 100644
--- a/src/nasal_builtin.h
+++ b/src/nasal_builtin.h
@@ -54,11 +54,6 @@ var builtin_num(var*, gc&);
 var builtin_pop(var*, gc&);
 var builtin_str(var*, gc&);
 var builtin_size(var*, gc&);
-var builtin_u32xor(var*, gc&);
-var builtin_u32and(var*, gc&);
-var builtin_u32or(var*, gc&);
-var builtin_u32nand(var*, gc&);
-var builtin_u32not(var*, gc&);
 var builtin_time(var*, gc&);
 var builtin_contains(var*, gc&);
 var builtin_delete(var*, gc&);
@@ -84,10 +79,6 @@ var builtin_tell(var*, gc&);
 var builtin_readln(var*, gc&);
 var builtin_stat(var*, gc&);
 var builtin_eof(var*, gc&);
-var builtin_fld(var*, gc&);
-var builtin_sfld(var*, gc&);
-var builtin_setfld(var*, gc&);
-var builtin_buf(var*, gc&);
 var builtin_sleep(var*, gc&);
 var builtin_pipe(var*, gc&);
 var builtin_fork(var*, gc&);
diff --git a/src/nasal_codegen.cpp b/src/nasal_codegen.cpp
index 3101188..88b49d2 100644
--- a/src/nasal_codegen.cpp
+++ b/src/nasal_codegen.cpp
@@ -15,6 +15,7 @@ void codegen::load_native_function_table(nasal_builtin_table* table) {
 void codegen::init_native_function() {
     load_native_function_table(builtin);
     load_native_function_table(math_lib_native);
+    load_native_function_table(bits_native);
     load_native_function_table(coroutine_native);
     load_native_function_table(flight_gear_native);
 }
diff --git a/src/nasal_codegen.h b/src/nasal_codegen.h
index 3913790..da81f01 100644
--- a/src/nasal_codegen.h
+++ b/src/nasal_codegen.h
@@ -10,6 +10,7 @@
 
 #include "nasal_builtin.h"
 #include "coroutine.h"
+#include "bits_lib.h"
 #include "math_lib.h"
 #include "fg_props.h"