EVM Istanbul upgrade (#183)

Author: dustinxie

changelog/evm-istanbul.md

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+# EVM Istanbul upgrade
+
+Starting v1.3 the IoTeX blockchain supports EVM Istanbul, which brings upgrades
+that improve denial-of-service attack resilience, and adjust gas costs for EVM
+storage and zk-SNARKs and zk-STARKs, allowing privacy applications based on
+SNARK and STARK to scale at a cheaper cost.
+
+Here's the list of EIP adopted in the Istanbul upgrade:
+
+- [EIP-152](https://eips.ethereum.org/EIPS/eip-152) -- precompiled Blake2b to
+facilitate Zcash
+- [EIP-1108](https://eips.ethereum.org/EIPS/eip-1108) -- better bn256 library
+for faster EC computation and reduced gas cost
+- [EIP-1344](https://eips.ethereum.org/EIPS/eip-1344) -- adds the CHAINID opcode
+to return current chain's EIP-155 unique identifier inside smart contract
+- [EIP-1884](https://eips.ethereum.org/EIPS/eip-1884) -- repricing for trie-size
+-dependent opcodes
+- [EIP-2028](https://eips.ethereum.org/EIPS/eip-2028) -- transaction data gas cost
+reduction
+- [EIP-2200](https://eips.ethereum.org/EIPS/eip-2200) -- cost reduction of storage
+in the EVM
+
+## Gas cost change
+Here's a summary of gas cost change as a result of these EIPs
+
+| Precompiled contract | Address | Current gas cost | Updated gas cost |
+| --- | --- | --- | --- |
+| ECADD | 0x06 | 500 | 150 |
+| ECMUL | 0x07 | 40000 | 6000 |
+| Pairing check | 0x08 | 80000*k* + 100000 | 34000*k* + 45000 |
+
+*k* is the number of pairings being computed
+
+| Opcode | Address | Current gas cost | Updated gas cost |
+| --- | --- | --- | --- |
+| SLOAD | 0x54 | 200 | 800 |
+| BALANCE | 0x31 | 400 | 700 |
+| EXTCODEHASH | 0x3F | 400 | 700 |
+| SELFBALANCE | 0x47 | n/a | 5 |
+| Calldata | n/a | 68 per byte | 16 per byte |
+