From a6947fbc7086dccd4d70e1a2b6ad54df19b2235f Mon Sep 17 00:00:00 2001
From: Connor McLaughlin <stenzek@gmail.com>
Date: Thu, 29 Oct 2020 20:57:10 +1000
Subject: [PATCH] CDROM: Implement fast forward/rewind

---
 src/core/cdrom.cpp | 55 +++++++++++++++++++++++++++++++++++++++++++++-
 src/core/cdrom.h   |  4 ++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/src/core/cdrom.cpp b/src/core/cdrom.cpp
index c88d89db7..1e2d765c6 100644
--- a/src/core/cdrom.cpp
+++ b/src/core/cdrom.cpp
@@ -198,6 +198,10 @@ bool CDROM::DoState(StateWrapper& sw)
   sw.Do(&m_last_cdda_report_frame_nibble);
   sw.Do(&m_play_track_number_bcd);
   sw.Do(&m_async_command_parameter);
+
+  // TODO: Uncomment on the next save state version bump.
+  //sw.Do(&m_fast_forward_rate);
+
   sw.Do(&m_cd_audio_volume_matrix);
   sw.Do(&m_next_cd_audio_volume_matrix);
   sw.Do(&m_xa_last_samples);
@@ -228,6 +232,7 @@ bool CDROM::DoState(StateWrapper& sw)
       m_reader.QueueReadSector(requested_sector);
     UpdateCommandEvent();
     m_drive_event->SetState(!IsDriveIdle());
+    m_fast_forward_rate = 0;
   }
 
   return !sw.HasError();
@@ -946,6 +951,7 @@ void CDROM::ExecuteCommand()
             (m_drive_state == DriveState::Playing || (IsSeeking() && m_play_after_seek)))
         {
           Log_DevPrintf("Ignoring play command with no/same setloc, already playing/playing after seek");
+          m_fast_forward_rate = 0;
         }
         else
         {
@@ -960,6 +966,48 @@ void CDROM::ExecuteCommand()
       return;
     }
 
+    case Command::Forward:
+    {
+      if (m_drive_state != DriveState::Playing || !CanReadMedia())
+      {
+        SendErrorResponse(STAT_ERROR, ERROR_REASON_NOT_READY);
+      }
+      else
+      {
+        SendACKAndStat();
+
+        if (m_fast_forward_rate < 0)
+          m_fast_forward_rate = 0;
+
+        m_fast_forward_rate += static_cast<s8>(FAST_FORWARD_RATE_STEP);
+        m_fast_forward_rate = std::min<s8>(m_fast_forward_rate, static_cast<s8>(MAX_FAST_FORWARD_RATE));
+      }
+
+      EndCommand();
+      return;
+    }
+
+    case Command::Backward:
+    {
+      if (m_drive_state != DriveState::Playing || !CanReadMedia())
+      {
+        SendErrorResponse(STAT_ERROR, ERROR_REASON_NOT_READY);
+      }
+      else
+      {
+        SendACKAndStat();
+
+        if (m_fast_forward_rate > 0)
+          m_fast_forward_rate = 0;
+
+        m_fast_forward_rate -= static_cast<s8>(FAST_FORWARD_RATE_STEP);
+        m_fast_forward_rate = std::max<s8>(m_fast_forward_rate, -static_cast<s8>(MAX_FAST_FORWARD_RATE));
+      }
+
+      EndCommand();
+      return;
+    }
+
     case Command::Pause:
     {
       if (m_secondary_status.seeking)
@@ -1392,6 +1440,7 @@ void CDROM::BeginPlaying(u8 track_bcd, TickCount ticks_late /* = 0 */, bool afte
   Log_DebugPrintf("Starting playing CDDA track %x", track_bcd);
   m_last_cdda_report_frame_nibble = 0xFF;
   m_play_track_number_bcd = track_bcd;
+  m_fast_forward_rate = 0;
 
   // if track zero, start from current position
   if (track_bcd != 0)
@@ -1779,6 +1828,7 @@ void CDROM::DoSectorRead()
     ProcessDataSectorHeader(m_reader.GetSectorBuffer().data());
   }
 
+  u32 next_sector = m_current_lba + 1u;
   if (is_data_sector && m_drive_state == DriveState::Reading)
   {
     ProcessDataSector(m_reader.GetSectorBuffer().data(), subq);
@@ -1787,6 +1837,9 @@ void CDROM::DoSectorRead()
            (m_drive_state == DriveState::Playing || (m_drive_state == DriveState::Reading && m_mode.cdda)))
   {
     ProcessCDDASector(m_reader.GetSectorBuffer().data(), subq);
+
+    if (m_fast_forward_rate != 0)
+      next_sector = m_current_lba + SignExtend32(m_fast_forward_rate);
   }
   else if (m_drive_state != DriveState::Reading && m_drive_state != DriveState::Playing)
   {
@@ -1798,7 +1851,7 @@ void CDROM::DoSectorRead()
                       is_data_sector ? "data" : "audio", is_data_sector ? "reading" : "playing");
   }
 
-  m_reader.QueueReadSector(m_current_lba + 1u);
+  m_reader.QueueReadSector(next_sector);
 }
 
 void CDROM::ProcessDataSectorHeader(const u8* raw_sector)
diff --git a/src/core/cdrom.h b/src/core/cdrom.h
index 9c088c643..427ce0ced 100644
--- a/src/core/cdrom.h
+++ b/src/core/cdrom.h
@@ -69,6 +69,9 @@ private:
     AUDIO_FIFO_LOW_WATERMARK = 5,
 
     BASE_RESET_TICKS = 400000,
+
+    MAX_FAST_FORWARD_RATE = 12,
+    FAST_FORWARD_RATE_STEP = 4
   };
 
   static constexpr u8 INTERRUPT_REGISTER_MASK = 0x1F;
@@ -314,6 +317,7 @@ private:
   u8 m_last_cdda_report_frame_nibble = 0xFF;
   u8 m_play_track_number_bcd = 0xFF;
   u8 m_async_command_parameter = 0x00;
+  s8 m_fast_forward_rate = 0;
 
   std::array<std::array<u8, 2>, 2> m_cd_audio_volume_matrix{};
   std::array<std::array<u8, 2>, 2> m_next_cd_audio_volume_matrix{};