diff --git a/c/omni_lock_time_lock.h b/c/omni_lock_time_lock.h
index de9df57..357f83e 100644
--- a/c/omni_lock_time_lock.h
+++ b/c/omni_lock_time_lock.h
@@ -1,73 +1,18 @@
 #ifndef OMNI_LOCK_TIME_LOCK_H_
 #define OMNI_LOCK_TIME_LOCK_H_
 
-#define ERROR_INCORRECT_SINCE_FLAGS -23
-#define ERROR_INCORRECT_SINCE_VALUE -24
-/* since */
-#define SINCE_VALUE_BITS 56
-#define SINCE_VALUE_MASK 0x00ffffffffffffff
-#define SINCE_EPOCH_FRACTION_FLAG 0b00100000
-
-/* a and b are since value,
- return 0 if a is equals to b,
- return -1 if a is less than b,
- return 1 if a is greater than b */
-int epoch_number_with_fraction_cmp(uint64_t a, uint64_t b) {
-  static const size_t NUMBER_OFFSET = 0;
-  static const size_t NUMBER_BITS = 24;
-  static const uint64_t NUMBER_MAXIMUM_VALUE = (1 << NUMBER_BITS);
-  static const uint64_t NUMBER_MASK = (NUMBER_MAXIMUM_VALUE - 1);
-  static const size_t INDEX_OFFSET = NUMBER_BITS;
-  static const size_t INDEX_BITS = 16;
-  static const uint64_t INDEX_MAXIMUM_VALUE = (1 << INDEX_BITS);
-  static const uint64_t INDEX_MASK = (INDEX_MAXIMUM_VALUE - 1);
-  static const size_t LENGTH_OFFSET = NUMBER_BITS + INDEX_BITS;
-  static const size_t LENGTH_BITS = 16;
-  static const uint64_t LENGTH_MAXIMUM_VALUE = (1 << LENGTH_BITS);
-  static const uint64_t LENGTH_MASK = (LENGTH_MAXIMUM_VALUE - 1);
-
-  /* extract a epoch */
-  uint64_t a_epoch = (a >> NUMBER_OFFSET) & NUMBER_MASK;
-  uint64_t a_index = (a >> INDEX_OFFSET) & INDEX_MASK;
-  uint64_t a_len = (a >> LENGTH_OFFSET) & LENGTH_MASK;
-
-  /* extract b epoch */
-  uint64_t b_epoch = (b >> NUMBER_OFFSET) & NUMBER_MASK;
-  uint64_t b_index = (b >> INDEX_OFFSET) & INDEX_MASK;
-  uint64_t b_len = (b >> LENGTH_OFFSET) & LENGTH_MASK;
-
-  if (a_epoch < b_epoch) {
-    return -1;
-  } else if (a_epoch > b_epoch) {
-    return 1;
-  } else {
-    /* a and b is in the same epoch,
-       compare a_index / a_len <=> b_index / b_len
-     */
-    uint64_t a_block = a_index * b_len;
-    uint64_t b_block = b_index * a_len;
-    /* compare block */
-    if (a_block < b_block) {
-      return -1;
-    } else if (a_block > b_block) {
-      return 1;
-    } else {
-      return 0;
-    }
-  }
-}
+#include "ckb_utils.h"
+#define ERROR_INCORRECT_SINCE_FLAGS (-23)
+#define ERROR_INCORRECT_SINCE_VALUE (-24)
 
 /* check since,
  for all inputs the since field must have the exactly same flags with the since
  constraint, and the value of since must greater or equals than the since
- contstaint */
+ constraint */
 int check_since(uint64_t since) {
   size_t i = 0;
   uint64_t len = 0;
   uint64_t input_since;
-  /* the 8 msb is flag */
-  uint8_t since_flags = since >> SINCE_VALUE_BITS;
-  uint64_t since_value = since & SINCE_VALUE_MASK;
   int ret;
   while (1) {
     len = sizeof(uint64_t);
@@ -80,17 +25,12 @@ int check_since(uint64_t since) {
     if (ret != CKB_SUCCESS || len != sizeof(uint64_t)) {
       return ERROR_SYSCALL;
     }
-    uint8_t input_since_flags = input_since >> SINCE_VALUE_BITS;
-    uint64_t input_since_value = input_since & SINCE_VALUE_MASK;
-    if (since_flags != input_since_flags) {
+    int comparable = 1;
+    int cmp = ckb_since_cmp(since, input_since, &comparable);
+    if (!comparable) {
       return ERROR_INCORRECT_SINCE_FLAGS;
     }
-    if (input_since_flags == SINCE_EPOCH_FRACTION_FLAG) {
-      ret = epoch_number_with_fraction_cmp(input_since_value, since_value);
-      if (ret < 0) {
-        return ERROR_INCORRECT_SINCE_VALUE;
-      }
-    } else if (input_since_value < since_value) {
+    if (cmp == 1) {
       return ERROR_INCORRECT_SINCE_VALUE;
     }
     i += 1;
diff --git a/tests/omni_lock_rust/tests/test_multisig.rs b/tests/omni_lock_rust/tests/test_multisig.rs
index c826d5a..1041992 100644
--- a/tests/omni_lock_rust/tests/test_multisig.rs
+++ b/tests/omni_lock_rust/tests/test_multisig.rs
@@ -335,6 +335,45 @@ fn test_multisig_0_2_3_unlock_with_since_eq() {
     verify_result.expect("pass verification");
 }
 
+#[test]
+fn test_multisig_0_2_3_unlock_with_since_relative_eq() {
+    let mut data_loader = DummyDataLoader::new();
+
+    let mut config = TestConfig::new(IDENTITY_FLAGS_MULTISIG, false);
+    config.set_multisig(0, 2, 3);
+
+    let since = 0x8000_0000_8888_8888u64;
+    config.set_since(since, since);
+    let tx = gen_tx(&mut data_loader, &mut config);
+    let tx = sign_tx(&mut data_loader, tx, &mut config);
+    let resolved_tx = build_resolved_tx(&data_loader, &tx);
+
+    let mut verifier = verify_tx(resolved_tx, data_loader);
+    verifier.set_debug_printer(debug_printer);
+    let verify_result = verifier.verify(MAX_CYCLES);
+    verify_result.expect("pass verification");
+}
+
+#[test]
+fn test_multisig_0_2_3_unlock_with_since_relative_not_comparable() {
+    let mut data_loader = DummyDataLoader::new();
+
+    let mut config = TestConfig::new(IDENTITY_FLAGS_MULTISIG, false);
+    config.set_multisig(0, 2, 3);
+
+    let since = 0x8000_0000_8888_8888u64;
+    let since2 = 0x0000_0000_8888_8888u64;
+    config.set_since(since, since2);
+    let tx = gen_tx(&mut data_loader, &mut config);
+    let tx = sign_tx(&mut data_loader, tx, &mut config);
+    let resolved_tx = build_resolved_tx(&data_loader, &tx);
+
+    let mut verifier = verify_tx(resolved_tx, data_loader);
+    verifier.set_debug_printer(debug_printer);
+    let verify_result = verifier.verify(MAX_CYCLES);
+    assert_script_error(verify_result.unwrap_err(), ERROR_INCORRECT_SINCE_FLAGS)
+}
+
 #[test]
 fn test_multisig_0_2_3_unlock_with_since_flags() {
     let mut data_loader = DummyDataLoader::new();