Generalize FEC header formatting. (pt. 4)

webrtc/modules/rtp_rtcp/source/forward_error_correction_internal.h

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_MODULES_RTP_RTCP_SOURCE_FORWARD_ERROR_CORRECTION_INTERNAL_H_
 #define WEBRTC_MODULES_RTP_RTCP_SOURCE_FORWARD_ERROR_CORRECTION_INTERNAL_H_
 
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
 
-// Packet mask size in bytes (L bit is set).
-constexpr size_t kMaskSizeLBitSet = 6;
-// Packet mask size in bytes (L bit is cleared).
-constexpr size_t kMaskSizeLBitClear = 2;
+// Maximum number of media packets that can be protected
+// by these packet masks.
+constexpr size_t kUlpfecMaxMediaPackets = 48;
+
+// Packet mask size in bytes (given L bit).
+constexpr size_t kUlpfecPacketMaskSizeLBitClear = 2;
+constexpr size_t kUlpfecPacketMaskSizeLBitSet = 6;
+
+// Convenience constants.
+constexpr size_t kUlpfecMinPacketMaskSize = kUlpfecPacketMaskSizeLBitClear;
+constexpr size_t kUlpfecMaxPacketMaskSize = kUlpfecPacketMaskSizeLBitSet;
 
 namespace internal {
 
 class PacketMaskTable {
  public:
   PacketMaskTable(FecMaskType fec_mask_type, int num_media_packets);
   ~PacketMaskTable() {}
   FecMaskType fec_mask_type() const { return fec_mask_type_; }
   const uint8_t*** fec_packet_mask_table() const {
     return fec_packet_mask_table_;
@@ skipping 25 matching lines @@
 //                                     packet mask used, and a pointer to the
 //                                     corresponding packet masks.
 // \param[out] packet_mask             A pointer to hold the packet mask array,
 //                                     of size: num_fec_packets *
 //                                     "number of mask bytes".
 void GeneratePacketMasks(int num_media_packets, int num_fec_packets,
                          int num_imp_packets, bool use_unequal_protection,
                          const PacketMaskTable& mask_table,
                          uint8_t* packet_mask);
 
+// Given a sequence number spread (i.e., the difference between the largest

[danilchap, 2016/08/29 12:26:03]

'plus one' in the comment feels strange.
may be instead of describing how to calculate it, describe what it represent
e.g. number of packet with sequence number between smallest and largest. Or is
it just number of sequence numbers between smallest and largest?
Can also change the parameter name to 'num_protected_packets' or 'num_packets'

[brandtr, 2016/08/30 07:12:41]

Updated comment.

+// and smallest sequence number, plus one), returns the required packet
+// mask size.
+size_t PacketMaskSize(size_t seq_num_spread);
+
 // Inserts |num_zeros| zero columns into |new_mask| at position
 // |new_bit_index|. If the current byte of |new_mask| can't fit all zeros, the
 // byte will be filled with zeros from |new_bit_index|, but the next byte will
 // be untouched.
 void InsertZeroColumns(int num_zeros,
                        uint8_t* new_mask,
                        int new_mask_bytes,
                        int num_fec_packets,
                        int new_bit_index);
 
@@ skipping 10 matching lines @@
                 uint8_t* old_mask,
                 int old_mask_bytes,
                 int num_fec_packets,
                 int new_bit_index,
                 int old_bit_index);
 
 }  // namespace internal
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_FORWARD_ERROR_CORRECTION_INTERNAL_H_