content: /*
   * HalfNES by Andrew Hoffman
   * Licensed under the GNU GPL Version 3. See LICENSE file
   */
  package com.grapeshot.halfnes.mappers;
  
  /**
   * Speed optimization for NROM games: copy everything to linear mapping and
   * don't use the bankswitching capability at all
   *
   * thanks to Stephen Chin - steveonjava@gmail.com
   */
  public class NromMapper extends Mapper {
  
      @Override
      public void loadrom() throws BadMapperException {
          super.loadrom();
          //copy the whole rom around so we need to do less math
  
          int[] shiftedprg = new int[65536];
          System.arraycopy(prg, 0, shiftedprg, 0x8000, prg.length);
          if (prgsize <= 16384) {
              //double up the rom if 16k
              System.arraycopy(prg, 0, shiftedprg, 0xc000, prg.length);
          }
          prg = shiftedprg;
      }
  
      @Override
      public int cartRead(final int addr) {
          if (addr >= 0x8000) {
              return prg[addr];
          } else if (addr >= 0x6000 && hasprgram) {
              return prgram[addr & 0x1fff];
          }
          return addr >> 8; //open bus
      }
  
      @Override
      public int ppuRead(int addr) {
          if (addr < 0x2000) {
              //math is hard let's go shopping
              return chr[addr];
          } else {
              switch (addr & 0xc00) {
                  case 0:
                      return nt0[addr & 0x3ff];
                  case 0x400:
                      return nt1[addr & 0x3ff];
                  case 0x800:
                      return nt2[addr & 0x3ff];
                  case 0xc00:
                  default:
                      if (addr >= 0x3f00) {
                          addr &= 0x1f;
                          if (addr >= 0x10 && ((addr & 3) == 0)) {
                              addr -= 0x10;
                          }
                          return ppu.pal[addr];
                      } else {
                          return nt3[addr & 0x3ff];
                      }
              }
          }
      }
  }
  