diff --git a/nekolib-src/ds/rs01_dict/src/lib.rs b/nekolib-src/ds/rs01_dict/src/lib.rs
index 76a5a4976d..3dd2f549f4 100644
--- a/nekolib-src/ds/rs01_dict/src/lib.rs
+++ b/nekolib-src/ds/rs01_dict/src/lib.rs
@@ -20,14 +20,16 @@ const POW2_SMALL: usize = 1 << SMALL;
 const RANK_LOOKUP: [[u16; SMALL]; POW2_SMALL] =
     rank_lookup::<SMALL, POW2_SMALL>();
 
-const fn rank_lookup<const SMALL: usize, const POW2_SMALL: usize>()
--> [[u16; SMALL]; POW2_SMALL] {
-    let mut table = [[0; SMALL]; POW2_SMALL];
+const fn rank_lookup<
+    const MAX_LEN: usize,      // log(n)/2
+    const BIT_PATTERNS: usize, // sqrt(n)
+>() -> [[u16; MAX_LEN]; BIT_PATTERNS] {
+    let mut table = [[0; MAX_LEN]; BIT_PATTERNS];
     let mut i = 0;
-    while i < (1 << SMALL) {
+    while i < BIT_PATTERNS {
         table[i][0] = (i & 1) as u16;
         let mut j = 1;
-        while j < SMALL {
+        while j < MAX_LEN {
             table[i][j] = table[i][j - 1] + (i >> j & 1) as u16;
             j += 1;
         }
@@ -36,6 +38,34 @@ const fn rank_lookup<const SMALL: usize, const POW2_SMALL: usize>()
     table
 }
 
+const fn select_lookup<
+    const BIT_PATTERNS: usize, // 2^(branch * large)
+    const BRANCH: usize,       // sqrt(log(n))
+    const MAX_ONES: usize,     // log(n)^2
+    const LG2_MAX_ONES: usize, // O(log(log(n)))
+>() -> [[u16; MAX_ONES]; BIT_PATTERNS] {
+    let mut table = [[0; MAX_ONES]; BIT_PATTERNS];
+    let mut i = 0;
+    while i < BIT_PATTERNS {
+        let mut j = 0;
+        let mut index = 0;
+        while j < BRANCH {
+            // [0011, 0100, 0010] (0b_0010_0100_0011)
+            // [0, 0, 0, 1, 1, 1, 1, 2, 2, 3, ...]
+            let count = i >> (j * LG2_MAX_ONES) & !(!0 << LG2_MAX_ONES);
+            let mut k = 0;
+            while k < count && index < MAX_ONES {
+                table[i][index] = j as u16;
+                index += 1;
+                k += 1;
+            }
+            j += 1;
+        }
+        i += 1;
+    }
+    table
+}
+
 struct RankPreprocess<const LARGE: usize, const SMALL: usize> {
     buf: Vec<u64>,
 
@@ -146,6 +176,12 @@ fn test_rank_lookup() {
     assert_eq!(&table[0b111][0..3], [1, 2, 3]);
 }
 
+#[test]
+fn test_select_lookup() {
+    let table = select_lookup::<4096, 3, 16, 4>();
+    assert_eq!(&table[0b_0010_0100_0011][0..9], [0, 0, 0, 1, 1, 1, 1, 2, 2]);
+}
+
 #[test]
 fn sanity_check() {
     let a = bitvec!(b"000 010 110 000; 111 001 000 011; 000 000 010 010");