From 438663e7fc11657d109b0b055aed2c0db1328f55 Mon Sep 17 00:00:00 2001
From: Seth Hampson <shampson@webrtc.org>
Date: Tue, 9 Jan 2018 11:14:14 -0800
Subject: [PATCH] DCHECKS added to GetSimulcastConfig.
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GetSimulcastConfig should never return an empty vector of VideoStreams, because lower layers in the code expect atleast one VideoStream. It should also never be given input of max_streams equal to 0.

Bug: webrtc:8648
Change-Id: I60f59b3b267a732f07001e4c8a7fa64963802887
Reviewed-on: https://webrtc-review.googlesource.com/38061
Commit-Queue: Erik Språng <sprang@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21545}
---
 media/engine/simulcast.cc | 48 ++++++++-------------------------------
 1 file changed, 9 insertions(+), 39 deletions(-)

diff --git a/media/engine/simulcast.cc b/media/engine/simulcast.cc
index f815256f5b..aa042468ad 100644
--- a/media/engine/simulcast.cc
+++ b/media/engine/simulcast.cc
@@ -69,31 +69,23 @@ void GetSimulcastSsrcs(const StreamParams& sp, std::vector<uint32_t>* ssrcs) {
   }
 }
 
-void MaybeExchangeWidthHeight(int* width, int* height) {
-  // |kSimulcastFormats| assumes |width| >= |height|. If not, exchange them
-  // before comparing.
-  if (*width < *height) {
-    int temp = *width;
-    *width = *height;
-    *height = temp;
-  }
-}
-
 int FindSimulcastFormatIndex(int width, int height) {
-  MaybeExchangeWidthHeight(&width, &height);
-
+  RTC_DCHECK_GE(width, 0);
+  RTC_DCHECK_GE(height, 0);
   for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
     if (width * height >=
         kSimulcastFormats[i].width * kSimulcastFormats[i].height) {
       return i;
     }
   }
+  RTC_NOTREACHED();
   return -1;
 }
 
 int FindSimulcastFormatIndex(int width, int height, size_t max_layers) {
-  MaybeExchangeWidthHeight(&width, &height);
-
+  RTC_DCHECK_GE(width, 0);
+  RTC_DCHECK_GE(height, 0);
+  RTC_DCHECK_GT(max_layers, 0);
   for (uint32_t i = 0; i < arraysize(kSimulcastFormats); ++i) {
     if (width * height >=
             kSimulcastFormats[i].width * kSimulcastFormats[i].height &&
@@ -101,6 +93,7 @@ int FindSimulcastFormatIndex(int width, int height, size_t max_layers) {
       return i;
     }
   }
+  RTC_NOTREACHED();
   return -1;
 }
 
@@ -113,51 +106,30 @@ int NormalizeSimulcastSize(int size, size_t simulcast_layers) {
 
 size_t FindSimulcastMaxLayers(int width, int height) {
   int index = FindSimulcastFormatIndex(width, height);
-  if (index == -1) {
-    return -1;
-  }
   return kSimulcastFormats[index].max_layers;
 }
 
-// TODO(marpan): Investigate if we should return 0 instead of -1 in
-// FindSimulcast[Max/Target/Min]Bitrate functions below, since the
-// codec struct max/min/targeBitrates are unsigned.
 int FindSimulcastMaxBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
-  if (format_index == -1) {
-    return -1;
-  }
   return kSimulcastFormats[format_index].max_bitrate_kbps * 1000;
 }
 
 int FindSimulcastTargetBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
-  if (format_index == -1) {
-    return -1;
-  }
   return kSimulcastFormats[format_index].target_bitrate_kbps * 1000;
 }
 
 int FindSimulcastMinBitrateBps(int width, int height) {
   const int format_index = FindSimulcastFormatIndex(width, height);
-  if (format_index == -1) {
-    return -1;
-  }
   return kSimulcastFormats[format_index].min_bitrate_kbps * 1000;
 }
 
-bool SlotSimulcastMaxResolution(size_t max_layers, int* width, int* height) {
+void SlotSimulcastMaxResolution(size_t max_layers, int* width, int* height) {
   int index = FindSimulcastFormatIndex(*width, *height, max_layers);
-  if (index == -1) {
-    RTC_LOG(LS_ERROR) << "SlotSimulcastMaxResolution";
-    return false;
-  }
-
   *width = kSimulcastFormats[index].width;
   *height = kSimulcastFormats[index].height;
   RTC_LOG(LS_INFO) << "SlotSimulcastMaxResolution to width:" << *width
                    << " height:" << *height;
-  return true;
 }
 
 int GetTotalMaxBitrateBps(const std::vector<webrtc::VideoStream>& streams) {
@@ -206,9 +178,7 @@ std::vector<webrtc::VideoStream> GetSimulcastConfig(size_t max_streams,
     // If the number of SSRCs in the group differs from our target
     // number of simulcast streams for current resolution, switch down
     // to a resolution that matches our number of SSRCs.
-    if (!SlotSimulcastMaxResolution(max_streams, &width, &height)) {
-      return std::vector<webrtc::VideoStream>();
-    }
+    SlotSimulcastMaxResolution(max_streams, &width, &height);
     num_simulcast_layers = max_streams;
   }
   std::vector<webrtc::VideoStream> streams;