Merge pull request bitcoin-core#100 from kallewoof/202112-tap-253

bug-fix: prefix compact size function
saleembelto · Dec 17, 2021 · a43374e · a43374e
2 parents c5f51a1 + ac02730
commit a43374e
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Showing 4 changed files with 67 additions and 9 deletions.
diff --git a/functions.cpp b/functions.cpp
@@ -253,6 +253,7 @@ int _e_jacobi_sym(Value&& pv)  { pv.do_jacobi_symbol(); pv.println(); return 0;
 int _e_tagged_hash(Value&& pv) { pv.do_tagged_hash(); pv.println(); return 0; }
 int _e_taproot_tweak_pubkey(Value&& pv) { pv.do_taproot_tweak_pubkey(); pv.println(); return 0; }
 int _e_prefix_compact_size(Value&& pv) { pv.do_prefix_compact_size(); pv.println(); return 0; }
+int _e_len(Value&& pv) { pv.do_len(); pv.println(); return 0; }
 #ifdef ENABLE_DANGEROUS
 int _e_taproot_tweak_seckey(Value&& pv) { pv.do_taproot_tweak_seckey(); pv.println(); return 0; }
 int _e_encode_wif(Value&& pv)    { kerl_set_sensitive(true); pv.do_encode_wif(); pv.println(); return 0; }
@@ -288,6 +289,7 @@ static const tf_t tfs[] = {
     TF ("[message] perform HASH256 (SHA256(SHA256(message))", hash256),
     TF ("[*]       convert into a hex string", hex),
     TF ("[arg]     convert into an integer", int),
+    TF ("[*]       show length of expression in bytes", len),
     TFN("[n] ([k]) calculate the Jacobi symbol for n modulo k, where k defaults to the secp256k1 field size", "jacobi-symbol", jacobi_sym),
     TFN("[value] prefix [value] with its compact size encoded byte length", "prefix-compact-size", prefix_compact_size),
     TFN("[pubkey] convert the given pubkey into an x-only pubkey, as those used in taproot/tapscript", "pubkey-to-xpubkey", pubkey_to_xpubkey),

diff --git a/test/value.cpp b/test/value.cpp
@@ -102,6 +102,56 @@ TEST_CASE("Single entry values are interpreted correctly", "[single-entry-values
     }
 }
 
+TEST_CASE("Compact size encoder", "[compact-size]") {
+    SECTION("Fitting in 1 byte") {
+        std::string s = "0x";
+        for (uint8_t i = 1; i < 253; ++i) {
+            s += strprintf("%02x", i);
+            Value v(s.c_str());
+            v.do_prefix_compact_size();
+            REQUIRE(v.data[0] == i);
+        }
+        s += "fd"; // -> 253 bytes -> 0xfd (16 bit) + LE(253) == 0xfdfd00
+        {
+            Value v(s.c_str());
+            v.do_prefix_compact_size();
+            REQUIRE((uint32_t)v.data[0] == 0xfd); // 2 byte size
+            REQUIRE((uint32_t)v.data[1] == 0xfd); // 253 (lower byte)
+            REQUIRE((uint32_t)v.data[2] == 0x00); // 00 (higher byte)
+        }
+        s += "feff000102"; // -> 258 bytes -> 0xfd + LE(258) == 0xfd0201
+        {
+            Value v(s.c_str());
+            v.do_prefix_compact_size();
+            REQUIRE((uint32_t)v.data[0] == 0xfd); // 2 byte size
+            REQUIRE((uint32_t)v.data[1] == 0x02); // 02 (lower byte)
+            REQUIRE((uint32_t)v.data[2] == 0x01); // 01 (higher byte)
+        }
+        {
+            Value v("0x00");
+            v.data.resize(65537);
+            v.do_prefix_compact_size();
+            // 65537 = 0x010001 = 0xfe (32 bit) + LE(65537) = 0xfc01000100
+            REQUIRE((uint32_t)v.data[0] == 0xfe); // 4 byte size
+            REQUIRE((uint32_t)v.data[1] == 0x01); // 01 (lowest byte)
+            REQUIRE((uint32_t)v.data[2] == 0x00); // 00 (lower byte)
+            REQUIRE((uint32_t)v.data[3] == 0x01); // 01 (higher byte)
+            REQUIRE((uint32_t)v.data[4] == 0x00); // 01 (highest byte)
+        }
+        {
+            Value v("0x00");
+            v.data.resize(65538);
+            v.do_prefix_compact_size();
+            // 65538 = 0x010002 = 0xfe (32 bit) + LE(65538) = 0xfc02000100
+            REQUIRE((uint32_t)v.data[0] == 0xfe); // 4 byte size
+            REQUIRE((uint32_t)v.data[1] == 0x02); // 02 (lowest byte)
+            REQUIRE((uint32_t)v.data[2] == 0x00); // 00 (lower byte)
+            REQUIRE((uint32_t)v.data[3] == 0x01); // 01 (higher byte)
+            REQUIRE((uint32_t)v.data[4] == 0x00); // 01 (highest byte)
+        }
+    }
+}
+
 TEST_CASE("Script or not to script", "[script-notscript]") {
     SECTION("515293 becomes the number, not the script") {
         Value notascript("515293");

diff --git a/value.cpp b/value.cpp
@@ -251,17 +251,22 @@ void Value::do_not_op() {
 
 void Value::do_prefix_compact_size() {
     data_value();
-    uint8_t sz8 = 0;
+    std::vector<uint8_t> prefix;
     size_t data_len = data.size();
-    #define DLW(type) \
-        if (sz8) data.insert(data.begin(), &sz8, &sz8 + 1);\
-        type t = (type)data_len;\
-        data.insert(data.begin(), &t, &t + sizeof(type));\
+    #define DLW(sz) \
+        for (size_t i = 0; i < sz; ++i) { prefix.push_back(data_len & 0xff); data_len >>= 8; } \
+        data.insert(data.begin(), prefix.begin(), prefix.end()); \
         return
-    if (data_len < 253) { DLW(uint8_t); }
-    if (data_len <= std::numeric_limits<unsigned short>::max()) { sz8 = 253; DLW(uint16_t); }
-    if (data_len <= std::numeric_limits<unsigned int>::max()) { sz8 = 254; DLW(uint32_t); }
-    sz8 = 255; DLW(uint64_t);
+    if (data_len < 253) { DLW(1); }
+    if (data_len <= std::numeric_limits<unsigned short>::max()) { prefix.push_back(253); DLW(2); }
+    if (data_len <= std::numeric_limits<unsigned int>::max()) { prefix.push_back(254); DLW(4); }
+    prefix.push_back(255); DLW(8);
+}
+
+void Value::do_len() {
+    data_value();
+    int64 = (int64_t)data.size();
+    type = T_INT;
 }
 
 std::vector<uint8_t> gen_taproot_tagged_hash(const std::string& tag, const std::vector<uint8_t>& msg) {

diff --git a/value.h b/value.h
@@ -527,6 +527,7 @@ struct Value {
     void do_taproot_tweak_pubkey();
     void do_jacobi_symbol();
     void do_prefix_compact_size();
+    void do_len();
 #ifdef ENABLE_DANGEROUS
     void do_taproot_tweak_seckey();
     void do_combine_privkeys();