Fix margin call price calculation

libraries/chain/asset.cpp

@@ -99,26 +99,21 @@ namespace graphene { namespace chain {
       }
       price price::max( asset_id_type base, asset_id_type quote ) { return asset( share_type(GRAPHENE_MAX_SHARE_SUPPLY), base ) / asset( share_type(1), quote); }
       price price::min( asset_id_type base, asset_id_type quote ) { return asset( 1, base ) / asset( GRAPHENE_MAX_SHARE_SUPPLY, quote); }
-
+ 
       /**
-       *  The call price is defined so that the collateral is able to purchase debt * collateral ratio.
+       *  The black swan price is defined as debt/collateral, we want to perform a margin call
+       *  before debt == collateral.   Given a debt/collateral ratio of 1 USD / CORE and
+       *  a maintenance collateral requirement of 2x we can define the call price to be
+       *  2 USD / CORE.   
        *
-       *  Give a margin order with @ref debt and @ref collateral we can infer the market price that
+       *  This method divides the collateral by the maintenance collateral ratio to derive
-       *  would be necessary to maintain the invariant that the collateral can purchase debt * collateral ratio
+       *  a call price for the given black swan ratio.
-       *
-       *  (debt / collateral_ratio) /  collateral  == fair market price 
-       *
-       *  Stated another way:
-       *
-       *  C * R  / D
-       *
-       *  This method only works if attempting to calculate the call price from a margin position. 
        */
       price price::call_price(const asset& debt, const asset& collateral, uint16_t collateral_ratio)
       { try {
          fc::uint128 tmp( collateral.amount.value );
-         tmp *= collateral_ratio - 1000;
+         tmp *= 1000;
-         tmp /= 1000;
+         tmp /= collateral_ratio;
          FC_ASSERT( tmp <= GRAPHENE_MAX_SHARE_SUPPLY );
          return asset( tmp.to_uint64(), collateral.asset_id) / debt;
       } FC_CAPTURE_AND_RETHROW( (debt)(collateral)(collateral_ratio) ) }

libraries/chain/call_order_evaluator.cpp

@@ -106,7 +106,7 @@ void_result call_order_update_evaluator::do_apply(const call_order_update_operat
          call.borrower = o.funding_account;
          call.collateral = o.delta_collateral.amount;
          call.debt = o.delta_debt.amount;
-         call.call_price = ~price::call_price(o.delta_debt, o.delta_collateral,
+         call.call_price = price::call_price(o.delta_debt, o.delta_collateral,
                                              _bitasset_data->current_feed.maintenance_collateral_ratio);
       });
    }
@@ -117,7 +117,7 @@ void_result call_order_update_evaluator::do_apply(const call_order_update_operat
       d.modify( *call_obj, [&]( call_order_object& call ){
           call.collateral += o.delta_collateral.amount;
           call.debt       += o.delta_debt.amount;
-          call.call_price  =  ~price::call_price(call.get_debt(), call.get_collateral(),
+          call.call_price  =  price::call_price(call.get_debt(), call.get_collateral(),
                                                 _bitasset_data->current_feed.maintenance_collateral_ratio);
       });
    }

libraries/chain/db_market.cpp

@@ -333,6 +333,7 @@ bool database::check_call_orders( const asset_object& mia, bool enable_black_swa
     auto max_price = price::max( mia.id, bitasset.options.short_backing_asset );
     // stop when limit orders are selling too little USD for too much CORE
     auto min_price = bitasset.current_feed.max_short_squeeze_price();
+    /*
  //   edump((bitasset.current_feed));
     edump((min_price.to_real())(min_price));
     edump((max_price.to_real())(max_price));
@@ -350,6 +351,7 @@ bool database::check_call_orders( const asset_object& mia, bool enable_black_swa
        wdump((max_price)(max_price.to_real()));
        wdump((min_price)(min_price.to_real()));
     }
+    */
 
     assert( max_price.base.asset_id == min_price.base.asset_id );
      wlog( "from ${a} Debt/Col to ${b} Debt/Col ", ("a", max_price.to_real())("b",min_price.to_real()) );

libraries/fc

@@ -1 +1 @@
-Subproject commit dde8ed9d7ab49807f2556488c0815f3741b11e00
+Subproject commit c09035dba0cdab7fcb2c11bf81aaeaffaa981f66

tests/tests/operation_tests.cpp

@@ -42,11 +42,19 @@ BOOST_FIXTURE_TEST_SUITE( operation_tests, database_fixture )
 BOOST_AUTO_TEST_CASE( feed_limit_logic_test )
 {
    try {
-      asset usd(100,1);
+      asset usd(1000,1);
-      asset core(100,0);
+      asset core(1000,0);
       price_feed feed;
       feed.settlement_price = usd / core;
 
+      // require 3x min collateral
+      auto swanp = usd / core;
+      auto callp = ~price::call_price( usd, core, 1750 );
+      // 1:1 collateral 
+      wdump((callp.to_real())(callp));
+      wdump((swanp.to_real())(swanp));
+      FC_ASSERT( callp.to_real() > swanp.to_real() );
+
       /*
       wdump((feed.settlement_price.to_real()));
       wdump((feed.maintenance_price().to_real()));