From 2342ade23c3e8a8855cfb55f9b15818978bfb333 Mon Sep 17 00:00:00 2001
From: Egor Tensin <egor@tensin.name>
Date: Thu, 18 Jun 2026 18:22:01 +0200
Subject: switch to if constexpr (..) to remove clutter

---
 aesxx/include/aesxx/api.hpp   | 66 +++++++++----------------------------------
 aesxx/include/aesxx/mode.hpp  | 21 +++-----------
 aesxx/utils/block_dumper.hpp  | 30 ++++++--------------
 aesxx/utils/decrypt_block.cpp |  2 +-
 aesxx/utils/encrypt_block.cpp |  2 +-
 5 files changed, 27 insertions(+), 94 deletions(-)

diff --git a/aesxx/include/aesxx/api.hpp b/aesxx/include/aesxx/api.hpp
index 1797a85..70891c9 100644
--- a/aesxx/include/aesxx/api.hpp
+++ b/aesxx/include/aesxx/api.hpp
@@ -48,72 +48,32 @@ void derive_decryption_keys(
     typename Types<algorithm>::RoundKeys& decryption_keys
 );
 
-template <
-    Algorithm algorithm,
-    Mode mode,
-    typename std::enable_if<ModeRequiresInitVector<mode>::value>::type* = nullptr>
+template <Algorithm algorithm, Mode mode>
 void encrypt_block(
     const typename Types<algorithm>::Block& plaintext,
     const typename Types<algorithm>::RoundKeys& round_keys,
     typename Types<algorithm>::Block& iv,
     typename Types<algorithm>::Block& ciphertext
-);
-
-template <
-    Algorithm algorithm,
-    Mode mode,
-    typename std::enable_if<!ModeRequiresInitVector<mode>::value>::type* = nullptr>
-void encrypt_block(
-    const typename Types<algorithm>::Block& plaintext,
-    const typename Types<algorithm>::RoundKeys& round_keys,
-    typename Types<algorithm>::Block& ciphertext
-);
-
-template <
-    Algorithm algorithm,
-    Mode mode,
-    typename std::enable_if<!ModeRequiresInitVector<mode>::value>::type* = nullptr>
-void encrypt_block(
-    const typename Types<algorithm>::Block& plaintext,
-    const typename Types<algorithm>::RoundKeys& round_keys,
-    typename Types<algorithm>::Block&,
-    typename Types<algorithm>::Block& ciphertext
 ) {
-    encrypt_block<algorithm, mode>(plaintext, round_keys, ciphertext);
+    if constexpr (mode_requires_init_vector(mode)) {
+        encrypt_block(plaintext, round_keys, iv, ciphertext);
+    } else {
+        encrypt_block(plaintext, round_keys, ciphertext);
+    }
 }
 
-template <
-    Algorithm algorithm,
-    Mode mode,
-    typename std::enable_if<ModeRequiresInitVector<mode>::value>::type* = nullptr>
+template <Algorithm algorithm, Mode mode>
 void decrypt_block(
     const typename Types<algorithm>::Block& ciphertext,
     const typename Types<algorithm>::RoundKeys& round_keys,
     typename Types<algorithm>::Block& iv,
     typename Types<algorithm>::Block& plaintext
-);
-
-template <
-    Algorithm algorithm,
-    Mode mode,
-    typename std::enable_if<!ModeRequiresInitVector<mode>::value>::type* = nullptr>
-void decrypt_block(
-    const typename Types<algorithm>::Block& ciphertext,
-    const typename Types<algorithm>::RoundKeys& round_keys,
-    typename Types<algorithm>::Block& plaintext
-);
-
-template <
-    Algorithm algorithm,
-    Mode mode,
-    typename std::enable_if<!ModeRequiresInitVector<mode>::value>::type* = nullptr>
-void decrypt_block(
-    const typename Types<algorithm>::Block& ciphertext,
-    const typename Types<algorithm>::RoundKeys& round_keys,
-    typename Types<algorithm>::Block&,
-    typename Types<algorithm>::Block& plaintext
 ) {
-    decrypt_block<algorithm, mode>(ciphertext, round_keys, plaintext);
+    if constexpr (mode_requires_init_vector(mode)) {
+        encrypt_block(plaintext, round_keys, iv, ciphertext);
+    } else {
+        encrypt_block(plaintext, round_keys, ciphertext);
+    }
 }
 
 template <Algorithm algorithm, Mode mode>
@@ -147,7 +107,7 @@ struct DecryptWrapper {
         typename Types<algorithm>::RoundKeys encryption_keys;
         expand_key<algorithm>(key, encryption_keys);
 
-        if (ModeUsesEncryptionKeysOnly<mode>::value) {
+        if constexpr (mode_uses_encryption_keys_only(mode)) {
             decryption_keys = encryption_keys;
         } else {
             derive_decryption_keys<algorithm>(encryption_keys, decryption_keys);
diff --git a/aesxx/include/aesxx/mode.hpp b/aesxx/include/aesxx/mode.hpp
index e4391a4..9fbcaae 100644
--- a/aesxx/include/aesxx/mode.hpp
+++ b/aesxx/include/aesxx/mode.hpp
@@ -13,26 +13,11 @@ namespace aes {
 
 typedef AES_Mode Mode;
 
-template <Mode mode>
-struct ModeRequiresInitVector : public std::true_type {};
-
-template <>
-struct ModeRequiresInitVector<AES_ECB> : public std::false_type {};
-
-template <Mode mode>
-struct ModeUsesEncryptionKeysOnly : public std::true_type {};
-
-inline bool mode_requires_init_vector(Mode mode) {
+inline constexpr bool mode_requires_init_vector(Mode mode) {
     return mode != AES_ECB;
 }
 
-template <>
-struct ModeUsesEncryptionKeysOnly<AES_ECB> : public std::false_type {};
-
-template <>
-struct ModeUsesEncryptionKeysOnly<AES_CBC> : public std::false_type {};
-
-inline bool mode_uses_encryption_keys_only(Mode mode) {
+inline constexpr bool mode_uses_encryption_keys_only(Mode mode) {
     return mode != AES_ECB && mode != AES_CBC;
 }
 
@@ -41,6 +26,7 @@ inline bool mode_uses_encryption_keys_only(Mode mode) {
     inline void encrypt_block<AES_##prefix, AES_ECB>(                               \
         const typename Types<AES_##prefix>::Block& plaintext,                       \
         const typename Types<AES_##prefix>::RoundKeys& encryption_keys,             \
+        typename Types<AES_##prefix>::Block&,                                       \
         typename Types<AES_##prefix>::Block& ciphertext                             \
     ) {                                                                             \
         ciphertext = aes_##prefix##_encrypt_block_ECB(plaintext, &encryption_keys); \
@@ -51,6 +37,7 @@ inline bool mode_uses_encryption_keys_only(Mode mode) {
     inline void decrypt_block<AES_##prefix, AES_ECB>(                               \
         const typename Types<AES_##prefix>::Block& ciphertext,                      \
         const typename Types<AES_##prefix>::RoundKeys& decryption_keys,             \
+        typename Types<AES_##prefix>::Block&,                                       \
         typename Types<AES_##prefix>::Block& plaintext                              \
     ) {                                                                             \
         plaintext = aes_##prefix##_decrypt_block_ECB(ciphertext, &decryption_keys); \
diff --git a/aesxx/utils/block_dumper.hpp b/aesxx/utils/block_dumper.hpp
index f05d41c..8284b67 100644
--- a/aesxx/utils/block_dumper.hpp
+++ b/aesxx/utils/block_dumper.hpp
@@ -70,30 +70,16 @@ void dump_wrapper(const aes::DecryptWrapper<algorithm, mode>& wrapper) {
     dump_decryption_keys<algorithm>(wrapper.decryption_keys);
 }
 
-template <
-    aes::Algorithm algorithm,
-    aes::Mode mode,
-    typename std::enable_if<aes::ModeRequiresInitVector<mode>::value>::type* = nullptr>
+template <aes::Algorithm algorithm, aes::Mode mode>
 void dump_next_iv(const aes::EncryptWrapper<algorithm, mode>& wrapper) {
-    dump_block<algorithm>("Next initialization vector", wrapper.iv);
+    if constexpr (aes::mode_requires_init_vector(mode)) {
+        dump_block<algorithm>("Next initialization vector", wrapper.iv);
+    }
 }
 
-template <
-    aes::Algorithm algorithm,
-    aes::Mode mode,
-    typename std::enable_if<!aes::ModeRequiresInitVector<mode>::value>::type* = nullptr>
-void dump_next_iv(const aes::EncryptWrapper<algorithm, mode>&) {}
-
-template <
-    aes::Algorithm algorithm,
-    aes::Mode mode,
-    typename std::enable_if<aes::ModeRequiresInitVector<mode>::value>::type* = nullptr>
+template <aes::Algorithm algorithm, aes::Mode mode>
 void dump_next_iv(const aes::DecryptWrapper<algorithm, mode>& wrapper) {
-    dump_block<algorithm>("Next initialization vector", wrapper.iv);
+    if constexpr (aes::mode_requires_init_vector(mode)) {
+        dump_block<algorithm>("Next initialization vector", wrapper.iv);
+    }
 }
-
-template <
-    aes::Algorithm algorithm,
-    aes::Mode mode,
-    typename std::enable_if<!aes::ModeRequiresInitVector<mode>::value>::type* = nullptr>
-void dump_next_iv(const aes::DecryptWrapper<algorithm, mode>&) {}
diff --git a/aesxx/utils/decrypt_block.cpp b/aesxx/utils/decrypt_block.cpp
index 317e6fd..f06221d 100644
--- a/aesxx/utils/decrypt_block.cpp
+++ b/aesxx/utils/decrypt_block.cpp
@@ -23,7 +23,7 @@ template <aes::Algorithm algorithm, aes::Mode mode>
 void decrypt_with_mode(const Input& input, bool verbose = false) {
     typename aes::Types<algorithm>::Block iv;
 
-    if (aes::ModeRequiresInitVector<mode>()) {
+    if constexpr (aes::mode_requires_init_vector(mode)) {
         aes::from_string<algorithm>(iv, input.iv);
         if (verbose)
             dump_iv<algorithm>(iv);
diff --git a/aesxx/utils/encrypt_block.cpp b/aesxx/utils/encrypt_block.cpp
index 5fdefd0..6bde766 100644
--- a/aesxx/utils/encrypt_block.cpp
+++ b/aesxx/utils/encrypt_block.cpp
@@ -23,7 +23,7 @@ template <aes::Algorithm algorithm, aes::Mode mode>
 void encrypt_with_mode(const Input& input, bool verbose = false) {
     typename aes::Types<algorithm>::Block iv;
 
-    if (aes::ModeRequiresInitVector<mode>::value) {
+    if constexpr (aes::mode_requires_init_vector(mode)) {
         aes::from_string<algorithm>(iv, input.iv);
         if (verbose)
             dump_iv<algorithm>(iv);
-- 
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