Improve GasMeter comments.

Author: ekpyron

libevmasm/GasMeter.h

@@ -226,13 +226,16 @@ class GasMeter
 	/// change with EVM versions)
 	static unsigned runGas(Instruction _instruction, langutil::EVMVersion _evmVersion);
 
-	/// @returns gas costs for push instructions (may change depending on EVM version)
+	/// @returns gas costs for the cheapest push instructions for the given @a _value
+	/// (may change depending on EVM version)
 	static unsigned pushGas(u256 _value, langutil::EVMVersion _evmVersion);
 
-	/// @returns gas costs for swap instructions (may change depending on EVM version)
+	/// @returns gas costs for the cheapest swap instructions for the given @a _depth
+	/// (may change depending on EVM version)
 	static unsigned swapGas(size_t _depth, langutil::EVMVersion _evmVersion);
 
-	/// @returns gas costs for dup instructions (may change depending on EVM version)
+	/// @returns gas costs for the cheapest dup instructions for the given @a _depth
+	/// (may change depending on EVM version)
 	static unsigned dupGas(size_t _depth, langutil::EVMVersion _evmVersion);
 
 	/// @returns the gas cost of the supplied data, depending whether it is in creation code, or not.