ale-sys 0.1.2

Rust bindings to the Arcade Learning Environment
Documentation 
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/* *****************************************************************************
 * A.L.E (Arcade Learning Environment)
 * Copyright (c) 2009-2013 by Yavar Naddaf, Joel Veness, Marc G. Bellemare and
 *   the Reinforcement Learning and Artificial Intelligence Laboratory
 * Released under the GNU General Public License; see License.txt for details.
 *
 * Based on: Stella  --  "An Atari 2600 VCS Emulator"
 * Copyright (c) 1995-2007 by Bradford W. Mott and the Stella team
 *
 * *****************************************************************************
 *
 * RomUtils.hpp
 *
 * Additional utilities to operate on RAM.
 * *****************************************************************************
 */

#include "RomUtils.hpp"

#include "System.hxx"

namespace ale {

/* reads a byte at a memory location between 0 and 128 */
int readRam(const System* system, int offset) {
  // peek modifies data-bus state, but is logically const from
  // the point of view of the RL interface
  System* sys = const_cast<System*>(system);

  return sys->peek((offset & 0x7F) + 0x80);
}

// Reads a byte from anywhere in the memory map between 0x0000 and 0xffff.
// Note that the 6507 CPU used in the Atari 2600 only has 13 address lines
// physically connected. According to documentation by Chris Wilkson found
// at: https://atariage.com/forums/topic/192418-mirrored-memory/
//
// The address ranges are therefore mirrored in the following way:
//
// ***************************************************
// * $0000-$003F = TIA Addresses $00-$3F (zero page) *
// * ----------------------------------------------- *
// *     mirror: $xyz0                               *
// *     x = {even}                                  *
// *     y = {anything}                              *
// *     z = {0, 4}                                  *
// ***************************************************
//
// **************************************
// * $0080-$00FF = RIOT RAM (zero page) *
// * ---------------------------------- *
// *     mirror: $xy80                  *
// *     x = {even}                     *
// *     y = {0,1,4,5,8,9,$C,$D}        *
// **************************************
//
// ****************************************
// * $0280-$029F = RIOT Addresses $00-$1F *
// * ------------------------------------ *
// *     mirror: $xyz0                    *
// *     x = {even}                       *
// *     y = {2,3,6,7,$A,$B,$E,$F}        *
// *     z = {8,$A,$C,$E}                 *
// ****************************************
//
// *****************************************
// * $1000-$1FFF = ROM Addresses $000-$FFF *
// * ------------------------------------- *
// *     mirror: $x000                     *
// *     x = {odd}                         *
// *****************************************
//
int readMappedRam(const System* system, int offset) {
  // peek modifies data-bus state, but is logically const from
  // the point of view of the RL interface
  System* sys = const_cast<System*>(system);
  return sys->peek(offset);
}

/* extracts a decimal value from a byte */
int getDecimalScore(int index, const System* system) {
  int score = 0;
  int digits_val = readRam(system, index);
  int right_digit = digits_val & 15;
  int left_digit = digits_val >> 4;
  score += ((10 * left_digit) + right_digit);

  return score;
}

/* extracts a decimal value from 2 bytes */
int getDecimalScore(int lower_index, int higher_index, const System* system) {
  int score = 0;
  int lower_digits_val = readRam(system, lower_index);
  int lower_right_digit = lower_digits_val & 15;
  int lower_left_digit = (lower_digits_val - lower_right_digit) >> 4;
  score += ((10 * lower_left_digit) + lower_right_digit);
  if (higher_index < 0) {
    return score;
  }
  int higher_digits_val = readRam(system, higher_index);
  int higher_right_digit = higher_digits_val & 15;
  int higher_left_digit = (higher_digits_val - higher_right_digit) >> 4;
  score += ((1000 * higher_left_digit) + 100 * higher_right_digit);
  return score;
}

/* extracts a decimal value from 3 bytes */
int getDecimalScore(int lower_index, int middle_index, int higher_index,
                    const System* system) {
  int score = getDecimalScore(lower_index, middle_index, system);
  int higher_digits_val = readRam(system, higher_index);
  int higher_right_digit = higher_digits_val & 15;
  int higher_left_digit = (higher_digits_val - higher_right_digit) >> 4;
  score += ((100000 * higher_left_digit) + 10000 * higher_right_digit);
  return score;
}

}  // namespace ale