improve name_suffix and add unit tests for them

Old version was more difficult to decipher and also did not work for 13
character names.

Confirmed that the old version and new version behave the same way with
randomly generated names that are no greater than 12 characters. (That
code is not in this commit.)

contracts/eosiolib/types.hpp

@@ -67,28 +67,36 @@ namespace eosio {
    #define N(X) ::eosio::string_to_name(#X)
 
 
-   static constexpr uint64_t name_suffix( uint64_t tmp ) {
-      uint64_t suffix = 0;
-      bool endsuffix = false;
-      uint32_t offset = 0;
-      for( uint32_t i = 0; i <= 12; ++i, ++offset ) {
-         auto p = tmp >> 59;
-         if( !p ) {
-            endsuffix = true;
-         } else {
-            if( !endsuffix ) {
-               suffix |= uint64_t(p) << (59-(5*offset));
-            }
+   static constexpr uint64_t name_suffix( uint64_t n ) {
+      uint32_t remaining_bits_after_last_actual_dot = 0;
+      uint32_t tmp = 0;
+      for( int32_t remaining_bits = 59; remaining_bits >= 4; remaining_bits -= 5 ) { // Note: remaining_bits must remain signed integer
+         // Get characters one-by-one in name in order from left to right (not including the 13th character)
+         auto c = (n >> remaining_bits) & 0x1Full;
+         if( !c ) { // if this character is a dot
+            tmp = static_cast<uint32_t>(remaining_bits);
+         } else { // if this character is not a dot
+            remaining_bits_after_last_actual_dot = tmp;
          }
-         if( endsuffix && p ) {
-            endsuffix = false;
-            offset = 0;
-            suffix = uint64_t(p) << (59-(5*offset));
-         }
-         tmp <<= 5;
       }
-      return suffix;
+
+      uint64_t thirteenth_character = n & 0x0Full;
+      if( thirteenth_character ) { // if 13th character is not a dot
+         remaining_bits_after_last_actual_dot = tmp;
+      }
+
+      if( remaining_bits_after_last_actual_dot == 0 ) // there is no actual dot in the name other than potentially leading dots
+         return n;
+
+      // At this point remaining_bits_after_last_actual_dot has to be within the range of 4 to 59 (and restricted to increments of 5).
+
+      // Mask for remaining bits corresponding to characters after last actual dot, except for 4 least significant bits (corresponds to 13th character).
+      uint64_t mask = (1ull << remaining_bits_after_last_actual_dot) - 16;
+      uint32_t shift = 64 - remaining_bits_after_last_actual_dot;
+
+      return ( ((n & mask) << shift) + (thirteenth_character << (shift-1)) );
    }
+
    /**
     *  @brief wraps a uint64_t to ensure it is only passed to methods that expect a Name
     *  @details wraps a uint64_t to ensure it is only passed to methods that expect a Name and

unittests/misc_tests.cpp

@@ -25,13 +25,65 @@
 using namespace eosio::chain;
 using namespace eosio::testing;
 
+#include <boost/random/mersenne_twister.hpp>
+#include <boost/random/uniform_int_distribution.hpp>
+
 namespace eosio
 {
 using namespace chain;
 using namespace std;
 
+static constexpr uint64_t name_suffix( uint64_t n ) {
+   uint32_t remaining_bits_after_last_actual_dot = 0;
+   uint32_t tmp = 0;
+   for( int32_t remaining_bits = 59; remaining_bits >= 4; remaining_bits -= 5 ) { // Note: remaining_bits must remain signed integer
+      // Get characters one-by-one in name in order from left to right (not including the 13th character)
+      auto c = (n >> remaining_bits) & 0x1Full;
+      if( !c ) { // if this character is a dot
+         tmp = static_cast<uint32_t>(remaining_bits);
+      } else { // if this character is not a dot
+         remaining_bits_after_last_actual_dot = tmp;
+      }
+   }
+
+   uint64_t thirteenth_character = n & 0x0Full;
+   if( thirteenth_character ) { // if 13th character is not a dot
+      remaining_bits_after_last_actual_dot = tmp;
+   }
+
+   if( remaining_bits_after_last_actual_dot == 0 ) // there is no actual dot in the name other than potentially leading dots
+      return n;
+
+   // At this point remaining_bits_after_last_actual_dot has to be within the range of 4 to 59 (and restricted to increments of 5).
+
+   // Mask for remaining bits corresponding to characters after last actual dot, except for 4 least significant bits (corresponds to 13th character).
+   uint64_t mask = (1ull << remaining_bits_after_last_actual_dot) - 16;
+   uint32_t shift = 64 - remaining_bits_after_last_actual_dot;
+
+   return ( ((n & mask) << shift) + (thirteenth_character << (shift-1)) );
+}
+
 BOOST_AUTO_TEST_SUITE(misc_tests)
 
+BOOST_AUTO_TEST_CASE(name_suffix_tests)
+{
+   BOOST_CHECK_EQUAL( name{name_suffix(0)}, name{0} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(abcdehijklmn))}, name{N(abcdehijklmn)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(abcdehijklmn1))}, name{N(abcdehijklmn1)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(abc.def))}, name{N(def)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(.abc.def))}, name{N(def)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(..abc.def))}, name{N(def)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(abc..def))}, name{N(def)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(abc.def.ghi))}, name{N(ghi)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(.abcdefghij))}, name{N(abcdefghij)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(.abcdefghij.1))}, name{N(1)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(a.bcdefghij))}, name{N(bcdefghij)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(a.bcdefghij.1))}, name{N(1)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(......a.b.c))}, name{N(c)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(abcdefhi.123))}, name{N(123)} );
+   BOOST_CHECK_EQUAL( name{name_suffix(N(abcdefhij.123))}, name{N(123)} );
+}
+
 /// Test processing of unbalanced strings
 BOOST_AUTO_TEST_CASE(json_from_string_test)
 {