anchor.diff:      };
       "head" = {
         fetchzipversion = 3;
  -      version = "2017-09-11";
  -      rev = "f8ae7afc1f61ed0db3b2f23f5d581706fe6ed677";
  -      sha256 = "8f844abe9495f6b610c952c14919e9e91cdc440a3d8d6936877daed0148f7452";
  +      version = "2017-12-04";
  +      rev = "7bd8751a81830815cdc8e4dfc88cad2c8ca15ca7";
  +      sha256 = "c9a8b0f1646b90e19e393fd309bdb61c671da087c079f9cc0f8b7e63a5a5a0f2";
       };
     };
     source = sources."${channel}";
  
positive.code:   nativeBuildInputs = [
      cmake
      ninja
      yasm
    ];
  
    buildInputs = [
      libx265-10
  
negative.code:     nativeBuildInputs = [
        cmake
        ninja
      ] ++ (
        if (channel == "head") then [
          nasm
        ] else [
          yasm  # Remove for > 2.6
        ]
      );
  
      buildInputs = optionals (elem targetSystem platforms.linux) [
        numactl
  