Line data    Source code

       1             : // Copyright (c) 2021-2024  Made to Order Software Corp.  All Rights Reserved
       2             : //
       3             : // https://snapwebsites.org/project/snapdev
       4             : // contact@m2osw.com
       5             : //
       6             : // This program is free software: you can redistribute it and/or modify
       7             : // it under the terms of the GNU General Public License as published by
       8             : // the Free Software Foundation, either version 3 of the License, or
       9             : // (at your option) any later version.
      10             : //
      11             : // This program is distributed in the hope that it will be useful,
      12             : // but WITHOUT ANY WARRANTY; without even the implied warranty of
      13             : // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      14             : // GNU General Public License for more details.
      15             : //
      16             : // You should have received a copy of the GNU General Public License
      17             : // along with this program.  If not, see <https://www.gnu.org/licenses/>.
      18             : 
      19             : /** \file
      20             :  * \brief Verify the saturated_subtract() function.
      21             :  *
      22             :  * This file implements tests to verify that the saturated_subtract() function
      23             :  * will indeed saturate the result on an underflow.
      24             :  */
      25             : 
      26             : // self
      27             : //
      28             : #include    "catch_main.h"
      29             : 
      30             : 
      31             : 
      32             : // snapdev
      33             : //
      34             : #include    <snapdev/math.h>
      35             : #include    <snapdev/ostream_int128.h>
      36             : 
      37             : 
      38             : // last include
      39             : //
      40             : #include    <snapdev/poison.h>
      41             : 
      42             : 
      43             : // __int128 is not ISO C++ yet
      44             : #pragma GCC diagnostic ignored "-Wpedantic"
      45             : 
      46             : 
      47           5 : CATCH_TEST_CASE("saturated_subtract_uint", "[math]")
      48             : {
      49           5 :     CATCH_START_SECTION("saturated_subtract_uint8: test all possible cases with 8 bits")
      50             :     {
      51         257 :         for(std::uint32_t n(0); n < 256; ++n)
      52             :         {
      53       65792 :             for(std::uint32_t m(0); m < 256; ++m)
      54             :             {
      55       65536 :                 std::int32_t expected(n - m);
      56       65536 :                 if(expected < 0)      // easy to test in this case
      57             :                 {
      58       32640 :                     expected = 0;
      59             :                 }
      60       65536 :                 std::int32_t const result(snapdev::saturated_subtract(
      61             :                               static_cast<std::uint8_t>(n)
      62       65536 :                             , static_cast<std::uint8_t>(m)));
      63       65536 :                 CATCH_REQUIRE(result == expected);
      64             :             }
      65             :         }
      66             :     }
      67           5 :     CATCH_END_SECTION()
      68             : 
      69           5 :     CATCH_START_SECTION("saturated_subtract_uint16: test many possible cases with 16 bits")
      70             :     {
      71        1344 :         for(std::uint32_t n(0); n < 65536; n += rand() % 100)
      72             :         {
      73     1780960 :             for(std::uint32_t m(0); m < 65536; m += rand() % 100)
      74             :             {
      75     1779617 :                 std::int32_t expected(n - m);
      76     1779617 :                 if(expected < 0)      // easy to test in this case
      77             :                 {
      78      892700 :                     expected = 0;
      79             :                 }
      80     1779617 :                 std::int32_t const result(snapdev::saturated_subtract(
      81             :                               static_cast<std::uint16_t>(n)
      82     1779617 :                             , static_cast<std::uint16_t>(m)));
      83     1779617 :                 CATCH_REQUIRE(result == expected);
      84             :             }
      85             :         }
      86             :     }
      87           5 :     CATCH_END_SECTION()
      88             : 
      89           5 :     CATCH_START_SECTION("saturated_subtract: test a few possible cases with 32 bits")
      90             :     {
      91             :         // no underflow at all
      92             :         {
      93           1 :             std::uint32_t const result(snapdev::saturated_subtract(
      94             :                           static_cast<std::uint32_t>(32'000)
      95             :                         , static_cast<std::uint32_t>(1'000)));
      96           1 :             CATCH_REQUIRE(result == 31'000UL);
      97             :         }
      98             : 
      99             :         // no underflow, but close
     100             :         {
     101           1 :             std::uint32_t const result(snapdev::saturated_subtract(
     102             :                           static_cast<std::uint32_t>(1'000)
     103             :                         , static_cast<std::uint32_t>(1'000)));
     104           1 :             CATCH_REQUIRE(result == std::numeric_limits<std::uint32_t>::min());
     105             :         }
     106             : 
     107             :         // underflow by 1
     108             :         {
     109           1 :             std::uint32_t const result(snapdev::saturated_subtract(
     110             :                           static_cast<std::uint32_t>(1'000)
     111             :                         , static_cast<std::uint32_t>(1'001)));
     112           1 :             CATCH_REQUIRE(result == std::numeric_limits<std::uint32_t>::min());
     113             :         }
     114             : 
     115             :         // definitive underflow
     116             :         {
     117           1 :             std::uint32_t const result(snapdev::saturated_subtract(
     118             :                           static_cast<std::uint32_t>(1'000)
     119             :                         , static_cast<std::uint32_t>(3'501)));
     120           1 :             CATCH_REQUIRE(result == std::numeric_limits<std::uint32_t>::min());
     121             :         }
     122             : 
     123             :         // max. underflow
     124             :         {
     125           1 :             std::uint32_t const result(snapdev::saturated_subtract(
     126             :                           std::numeric_limits<std::uint32_t>::min()
     127             :                         , std::numeric_limits<std::uint32_t>::max()));
     128           1 :             CATCH_REQUIRE(result == std::numeric_limits<std::uint32_t>::min());
     129             :         }
     130             :     }
     131           5 :     CATCH_END_SECTION()
     132             : 
     133           5 :     CATCH_START_SECTION("saturated_subtract_uint64: test a few possible cases with 64 bits")
     134             :     {
     135             :         // no underflow at all
     136             :         {
     137           1 :             std::uint64_t const result(snapdev::saturated_subtract(
     138             :                           static_cast<std::uint64_t>(32'000)
     139             :                         , static_cast<std::uint64_t>(1'000)));
     140           1 :             CATCH_REQUIRE(result == 31'000UL);
     141             :         }
     142             : 
     143             :         // no underflow, but close
     144             :         {
     145           1 :             std::uint64_t const result(snapdev::saturated_subtract(
     146             :                           static_cast<std::uint64_t>(1'000)
     147             :                         , static_cast<std::uint64_t>(1'000)));
     148           1 :             CATCH_REQUIRE(result == std::numeric_limits<std::uint64_t>::min());
     149             :         }
     150             : 
     151             :         // underflow by 1
     152             :         {
     153           1 :             std::uint64_t const result(snapdev::saturated_subtract(
     154             :                           static_cast<std::uint64_t>(1'000)
     155             :                         , static_cast<std::uint64_t>(1'001)));
     156           1 :             CATCH_REQUIRE(result == std::numeric_limits<std::uint64_t>::min());
     157             :         }
     158             : 
     159             :         // definitive underflow
     160             :         {
     161           1 :             std::uint64_t const result(snapdev::saturated_subtract(
     162             :                           static_cast<std::uint64_t>(1'000)
     163             :                         , static_cast<std::uint64_t>(3'501)));
     164           1 :             CATCH_REQUIRE(result == std::numeric_limits<std::uint64_t>::min());
     165             :         }
     166             : 
     167             :         // max. underflow
     168             :         {
     169           1 :             std::uint64_t const result(snapdev::saturated_subtract(
     170             :                           std::numeric_limits<std::uint64_t>::min()
     171             :                         , std::numeric_limits<std::uint64_t>::max()));
     172           1 :             CATCH_REQUIRE(result == std::numeric_limits<std::uint64_t>::min());
     173             :         }
     174             :     }
     175           5 :     CATCH_END_SECTION()
     176             : 
     177           5 :     CATCH_START_SECTION("saturated_subtract_uint128: test a few possible cases with 128 bits")
     178             :     {
     179             : #pragma GCC diagnostic push
     180             : #pragma GCC diagnostic ignored "-Wpedantic"
     181             :         // no underflow at all
     182             :         {
     183           1 :             unsigned __int128 const result(snapdev::saturated_subtract(
     184             :                           static_cast<unsigned __int128>(32'000)
     185             :                         , static_cast<unsigned __int128>(1'000)));
     186           1 :             CATCH_REQUIRE(result == 31'000UL);
     187             :         }
     188             : 
     189             :         // no underflow, but close
     190             :         {
     191           1 :             unsigned __int128 const result(snapdev::saturated_subtract(
     192             :                           static_cast<unsigned __int128>(1'000)
     193             :                         , static_cast<unsigned __int128>(1'000)));
     194           1 :             CATCH_REQUIRE(result == std::numeric_limits<unsigned __int128>::min());
     195             :         }
     196             : 
     197             :         // underflow by 1
     198             :         {
     199           1 :             unsigned __int128 const result(snapdev::saturated_subtract(
     200             :                           static_cast<unsigned __int128>(1'000)
     201             :                         , static_cast<unsigned __int128>(1'001)));
     202           1 :             CATCH_REQUIRE(result == std::numeric_limits<unsigned __int128>::min());
     203             :         }
     204             : 
     205             :         // definitive underflow
     206             :         {
     207           1 :             unsigned __int128 const result(snapdev::saturated_subtract(
     208             :                           static_cast<unsigned __int128>(3'501)
     209           1 :                         , std::numeric_limits<unsigned __int128>::max() - 1'000));
     210           1 :             CATCH_REQUIRE(result == std::numeric_limits<unsigned __int128>::min());
     211             :         }
     212             : 
     213             :         // max. underflow
     214             :         {
     215           1 :             unsigned __int128 const result(snapdev::saturated_subtract(
     216             :                           std::numeric_limits<unsigned __int128>::min()
     217             :                         , std::numeric_limits<unsigned __int128>::max()));
     218           1 :             CATCH_REQUIRE(result == std::numeric_limits<unsigned __int128>::min());
     219             :         }
     220             : #pragma GCC diagnostic pop
     221             :     }
     222           5 :     CATCH_END_SECTION()
     223           5 : }
     224             : 
     225             : 
     226             : // vim: ts=4 sw=4 et