// 0. If *gasleft* is less than or equal to 2300, fail the current call.
// 1. If current value equals new value (this is a no-op), SSTORE_NOOP_GAS gas is deducted.
// 1. If current value equals new value (this is a no-op), SLOAD_GAS is deducted.
// 2. If current value does not equal new value:
// 2.1. If original value equals current value (this storage slot has not been changed by the current execution context):
// 2.1.1. If original value is 0, SSTORE_INIT_GAS gas is deducted.
// 2.1.2. Otherwise, SSTORE_CLEAN_GAS gas is deducted. If new value is 0, add SSTORE_CLEAR_REFUND to refund counter.
// 2.2. If original value does not equal current value (this storage slot is dirty), SSTORE_DIRTY_GAS gas is deducted. Apply both of the following clauses:
// 2.1.1. If original value is 0, SSTORE_SET_GAS (20K) gas is deducted.
// 2.1.2. Otherwise, SSTORE_RESET_GAS gas is deducted. If new value is 0, add SSTORE_CLEARS_SCHEDULE to refund counter.
// 2.2. If original value does not equal current value (this storage slot is dirty), SLOAD_GAS gas is deducted. Apply both of the following clauses:
// 2.2.1. If original value is not 0:
// 2.2.1.1. If current value is 0 (also means that new value is not 0), subtract SSTORE_CLEAR_REFUND gas from refund counter. We can prove that refund counter will never go below 0.
// 2.2.1.2. If new value is 0 (also means that current value is not 0), add SSTORE_CLEAR_REFUND gas to refund counter.
// 2.2.1.1. If current value is 0 (also means that new value is not 0), subtract SSTORE_CLEARS_SCHEDULE gas from refund counter.
// 2.2.1.2. If new value is 0 (also means that current value is not 0), add SSTORE_CLEARS_SCHEDULE gas to refund counter.
// 2.2.2. If original value equals new value (this storage slot is reset):
// 2.2.2.1. If original value is 0, add SSTORE_INIT_REFUND to refund counter.
// 2.2.2.2. Otherwise, add SSTORE_CLEAN_REFUND gas to refund counter.
// 2.2.2.1. If original value is 0, add SSTORE_SET_GAS - SLOAD_GAS to refund counter.
// 2.2.2.2. Otherwise, add SSTORE_RESET_GAS - SLOAD_GAS gas to refund counter.