diff --git a/src/impl/algorithm.inc b/src/impl/algorithm.inc
index f099f28..db4b341 100644
--- a/src/impl/algorithm.inc
+++ b/src/impl/algorithm.inc
@@ -12,11 +12,11 @@
 
 #define MD5_CYC(w, s) (w = (w << s) | (w >> (32 - s)))
 
-#define MD5_STEP(i, f, a, b, c, d)                \
-    do {                                          \
-        a += f(b, c, d) + MD5_DATA(i) + MD5_T(i); \
-        MD5_CYC(a, MD5_S(i));                     \
-        a += b;                                   \
+#define MD5_STEP(i, f, a, b, c, d)            \
+    do {                                      \
+        a += f(b, c, d) + block[K(i)] + T(i); \
+        MD5_CYC(a, S(i));                     \
+        a += b;                               \
     } while (0)
 
 #define MD5_FF(i, ...) MD5_STEP((0x00 | i), MD5_F, __VA_ARGS__)
@@ -33,18 +33,34 @@
 #define MD5_UPDATE \
     MD5_ROUND(MD5_FF) MD5_ROUND(MD5_GG) MD5_ROUND(MD5_HH) MD5_ROUND(MD5_II)
 
-namespace md5::value {
+#include "sine.inc"
+
+namespace md5 {
+
+/// MD5 fixed constants in little endian.
+constexpr uint32_t MD5_A = 0x67452301;
+constexpr uint32_t MD5_B = 0xefcdab89;
+constexpr uint32_t MD5_C = 0x98badcfe;
+constexpr uint32_t MD5_D = 0x10325476;
+
+struct md5_ctx {
+    uint32_t A = MD5_A;
+    uint32_t B = MD5_B;
+    uint32_t C = MD5_C;
+    uint32_t D = MD5_D;
+    uint64_t size = 0; // processed size in byte
+};
 
 /// MD5 data block index, input between 0 and 63.
 consteval int K(int i) {
-    const int step[] = {1, 5, 3, 7};
-    const int begin[] = {0, 1, 5, 0};
+    const int step[4] = {1, 5, 3, 7};
+    const int begin[4] = {0, 1, 5, 0};
     return (begin[i >> 4] + step[i >> 4] * i) & 0b1111;
 }
 
 /// MD5 circular shift times, input between 0 and 63.
 consteval int S(int i) {
-    const int shift[][4] = {
+    const int shift[4][4] = {
         {7, 12, 17, 22},
         {5, 9, 14, 20},
         {4, 11, 16, 23},
@@ -59,4 +75,4 @@ consteval uint32_t T(int i) {
     return static_cast<uint32_t>(std::abs(val) * 0x100000000);
 }
 
-} // namespace md5::value
+} // namespace md5
diff --git a/src/impl/constexpr.inc b/src/impl/constexpr.inc
new file mode 100644
index 0000000..9820fdc
--- /dev/null
+++ b/src/impl/constexpr.inc
@@ -0,0 +1,99 @@
+#pragma once
+
+#include <array>
+
+namespace md5 {
+
+using BlockData = std::array<uint32_t, 16>;
+
+// TODO: test the compile speed of T function
+//static constexpr std::array<uint32_t, 64> kT = {
+//    T(0x00), T(0x01), T(0x02), T(0x03), T(0x04), T(0x05), T(0x06), T(0x07),
+//    T(0x08), T(0x09), T(0x0a), T(0x0b), T(0x0c), T(0x0d), T(0x0e), T(0x0f),
+//    T(0x10), T(0x11), T(0x12), T(0x13), T(0x14), T(0x15), T(0x16), T(0x17),
+//    T(0x18), T(0x19), T(0x1a), T(0x1b), T(0x1c), T(0x1d), T(0x1e), T(0x1f),
+//    T(0x20), T(0x21), T(0x22), T(0x23), T(0x24), T(0x25), T(0x26), T(0x27),
+//    T(0x28), T(0x29), T(0x2a), T(0x2b), T(0x2c), T(0x2d), T(0x2e), T(0x2f),
+//    T(0x30), T(0x31), T(0x32), T(0x33), T(0x34), T(0x35), T(0x36), T(0x37),
+//    T(0x38), T(0x39), T(0x3a), T(0x3b), T(0x3c), T(0x3d), T(0x3e), T(0x3f),
+//};
+
+static constexpr void BlockUpdate(md5_ctx *ctx, const BlockData &block) {
+    auto A = ctx->A;
+    auto B = ctx->B;
+    auto C = ctx->C;
+    auto D = ctx->D;
+
+    auto A_ = A;
+    auto B_ = B;
+    auto C_ = C;
+    auto D_ = D;
+
+    MD5_UPDATE
+
+    A += A_;
+    B += B_;
+    C += C_;
+    D += D_;
+
+    ctx->A = A;
+    ctx->B = B;
+    ctx->C = C;
+    ctx->D = D;
+}
+
+static constexpr uint8_t GetByte(const char *data, const uint64_t index,
+                                 const uint64_t len, const uint64_t padded_len) {
+    if (index < len) {
+        return data[index];
+    }
+    if (index == len) {
+        return 0x80;
+    }
+    if (index >= padded_len - 8) {
+        const uint64_t i = index - (padded_len - 8);
+        return static_cast<uint8_t>(((len * 8) >> (i * 8)) & 0xff);
+    }
+    return 0;
+}
+
+static constexpr uint32_t GetWord(const char *data, const uint64_t index,
+                                  const uint64_t len, const uint64_t padded_len) {
+    auto b0 = static_cast<uint32_t>(GetByte(data, index + 0, len, padded_len));
+    auto b1 = static_cast<uint32_t>(GetByte(data, index + 1, len, padded_len));
+    auto b2 = static_cast<uint32_t>(GetByte(data, index + 2, len, padded_len));
+    auto b3 = static_cast<uint32_t>(GetByte(data, index + 3, len, padded_len));
+    return b0 | (b1 << 8) | (b2 << 16) | (b3 << 24);
+}
+
+static constexpr BlockData GetBlock(const char *data, const uint64_t index,
+                                    const uint64_t len, const uint64_t padded_len) {
+    return BlockData {
+        GetWord(data, index + 0, len, padded_len),
+        GetWord(data, index + 4, len, padded_len),
+        GetWord(data, index + 8, len, padded_len),
+        GetWord(data, index + 12, len, padded_len),
+        GetWord(data, index + 16, len, padded_len),
+        GetWord(data, index + 20, len, padded_len),
+        GetWord(data, index + 24, len, padded_len),
+        GetWord(data, index + 28, len, padded_len),
+        GetWord(data, index + 32, len, padded_len),
+        GetWord(data, index + 36, len, padded_len),
+        GetWord(data, index + 40, len, padded_len),
+        GetWord(data, index + 44, len, padded_len),
+        GetWord(data, index + 48, len, padded_len),
+        GetWord(data, index + 52, len, padded_len),
+        GetWord(data, index + 56, len, padded_len),
+    };
+}
+
+inline constexpr CE MD5::HashCE(const char *data, uint64_t len) {
+    md5_ctx ctx;
+    const uint32_t padded_len = ((len + 64 + 8) / 64) * 64;
+    for (uint32_t index = 0; index < padded_len; index += 64) {
+        BlockUpdate(&ctx, GetBlock(data, index, len, padded_len));
+    }
+    return {ctx.A, ctx.B, ctx.C, ctx.D};
+}
+
+} // namespace md5
diff --git a/src/impl/core.cc b/src/impl/core.cc
index ce2b7f2..c6c7559 100644
--- a/src/impl/core.cc
+++ b/src/impl/core.cc
@@ -1,12 +1,6 @@
 #include <cstring>
 
 #include "md5.h"
-#include "sine.inc"
-#include "algorithm.inc"
-
-#define MD5_S(i)    value::S(i)
-#define MD5_T(i)    value::T(i)
-#define MD5_DATA(i) block[value::K(i)]
 
 namespace md5 {
 
diff --git a/src/impl/inline.inc b/src/impl/inline.inc
index e2641ae..f0eb470 100644
--- a/src/impl/inline.inc
+++ b/src/impl/inline.inc
@@ -31,4 +31,8 @@ inline std::string MD5::Hash(const void *data, uint64_t len) {
     return md5.Digest();
 }
 
+inline constexpr CE MD5::HashCE(const std::string_view &data) {
+    return HashCE(data.data(), data.size());
+}
+
 } // namespace md5
diff --git a/src/md5.h b/src/md5.h
index a7d682c..154115e 100644
--- a/src/md5.h
+++ b/src/md5.h
@@ -3,14 +3,22 @@
 #include <string>
 #include <cstdint>
 
+// TODO: remove if not using tuple
+#include <tuple>
+
 static_assert(sizeof(uintptr_t) == 8,
     "Project only works on 64-bits architecture.");
 
 static_assert(__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__,
     "Project only works on little-endian architecture.");
 
+#include "impl/algorithm.inc"
+
 namespace md5 {
 
+// TODO: return string or tuple result?
+using CE = std::tuple<uint32_t, uint32_t, uint32_t, uint32_t>;
+
 class MD5 {
 public:
     MD5() = default;
@@ -37,19 +45,12 @@ public:
     /// Calculate the md5 hash value of the specified data.
     static std::string Hash(const void *data, uint64_t len);
 
-private:
-    static constexpr uint32_t MD5_A = 0x67452301;
-    static constexpr uint32_t MD5_B = 0xefcdab89;
-    static constexpr uint32_t MD5_C = 0x98badcfe;
-    static constexpr uint32_t MD5_D = 0x10325476;
-
-    struct md5_ctx {
-        uint32_t A = MD5_A;
-        uint32_t B = MD5_B;
-        uint32_t C = MD5_C;
-        uint32_t D = MD5_D;
-        uint64_t size = 0; // processed size in byte
-    };
+    /// Calculate the md5 hash value of the specified data with constexpr.
+    static constexpr CE HashCE(const std::string_view &data);
+
+    /// Calculate the md5 hash value of the specified data with constexpr.
+    // TODO: using `const void *` or `const char *`
+    static constexpr CE HashCE(const char *data, uint64_t len);
 
 private:
     md5_ctx ctx_;
@@ -66,3 +67,4 @@ private:
 } // namespace md5
 
 #include "impl/inline.inc"
+#include "impl/constexpr.inc"