Set price per compute unit (#304)

* Set price per compute unit

* Fix comment

* Don't define CU_PRICE in header

Author: tompntn

pc/rpc_client.cpp

@@ -923,7 +923,7 @@ bool rpc::upd_price::build_tx(
   tx.add( *first.bhash_ ); // recent block hash
 
   // instructions section
-  tx.add_len( n + 1 ); // 1 compute limit instruction, n upd_price instruction(s)
+  tx.add_len( n + 1 + 1 ); // 1 compute limit instruction, 1 compute unit price instruction, n upd_price instruction(s)
 
   // Set compute limit
   tx.add( (uint8_t)( n + 3 ) ); // compute budget program id index in accounts list
@@ -933,6 +933,19 @@ bool rpc::upd_price::build_tx(
   tx.add( (uint8_t) 2 ); // SetComputeLimit enum variant
   tx.add( (uint32_t) CU_BUDGET_PER_IX * n ); // the budget (scaled for number of instructions)
 
+  // Requested price per compute unit, in micro lamports
+  // We want to pay 5000 lamports in total, so ((5000/20000) / 8) * (10^6)
+  // assuming upper bound of 20000 CUs and 8 instructions.
+  const uint64_t cu_price_micro_lamports = 31250;
+
+  // Set compute unit price
+  tx.add( (uint8_t)( n + 3 ) );
+  tx.add_len<0>(); // no accounts
+  // compute unit price instruction parameters
+  tx.add_len<sizeof(uint8_t) + sizeof(uint64_t)>(); // uint8_t enum variant + uint62_t compute price
+  tx.add( (uint8_t) 3 ); // SetComputePrice enum variant
+  tx.add( (uint64_t) cu_price_micro_lamports ); // price we are willing to pay per compute unit in Micro Lamports
+
   for ( unsigned i = 0; i < n; ++i ) {
     tx.add( (uint8_t)( n + 2 ) ); // program_id index
     tx.add_len< 3 >(); // 3 accounts: publish, symbol, sysvar

program/c/src/oracle/oracle.h

@@ -74,6 +74,7 @@ e79bc372baadecff
 403a9b432c
 */
 
+// correct
 const uint64_t compute_budget_program_id[] = {
   0x321721e56f460603UL,
   0xe79bc372baadecffUL,