all: replace Div/Mul with Rsh/Lsh if possible #29911

[gzliudan]

Proposed changes

Ref: ethereum#29911

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)
• Regular KTLO or any of the maintaince work. e.g code style
• CICD Improvement

Impacted Components

Which part of the codebase this PR will touch base on,

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• Consensus
• Account
• Network
• Geth
• Smart Contract
• External components
• Not sure (Please specify below)

Checklist

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• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
• Provide an end-to-end test plan in the PR description on how to manually test it on the devnet/testnet.
• Tested the backwards compatibility.
• Tested with XDC nodes running this version co-exist with those running the previous version.
• Relevant documentation has been updated as part of this PR
• N/A

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[AnilChinchawale]

@gzliudan conflict

[gzliudan]

@gzliudan conflict

done

[Copilot]

Pull request overview

This PR optimizes big integer arithmetic by replacing division and multiplication operations with bit shift operations where the divisor/multiplier is a power of 2. The changes replace Div(x, 2^n) with Rsh(x, n) and Mul(x, 2^n) with Lsh(x, n), which are mathematically equivalent and more efficient operations.

Changes:

• Replaced multiplication by powers of 2 (2, 4, 8, 16, 32) with left shift operations
• Replaced division by powers of 2 (2, 4, 8, 16, 32) with right shift operations
• Removed unused constants big4, big8, and big16 from core/vm/contracts.go

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/fuzzers/bn256/bn256_fuzz.go	Optimized scalar multiplication by 2 in BN256 fuzzer
internal/ethapi/transaction_args_test.go	Optimized max fee calculation in test
internal/ethapi/transaction_args.go	Optimized London fee defaults calculation
internal/ethapi/api.go	Optimized staker ROI calculations using right shift
eth/util/util.go	Optimized reward inflation halving calculations
eth/gasprice/gasprice.go	Optimized gas price suggestion calculations
crypto/secp256k1/curve.go	Optimized Jacobian doubling arithmetic
crypto/crypto.go	Optimized secp256k1 half N calculation
core/vm/privacy/ringct.go	Optimized compressed key deserialization
core/vm/contracts.go	Optimized modexp complexity and gas calculations, removed unused constants
core/types/transaction_signing.go	Critical bug: Changed deriveChainId to mutate input parameter
core/txpool/legacypool/legacypool_test.go	Optimized gas fee calculations in tests
contracts/trc21issuer/simulation/test/main.go	Optimized TRC21 gas price calculations
consensus/ethash/consensus.go	Optimized uncle reward calculations
XDCxlending/order_processor_test.go	Optimized test quantity calculations
XDCxlending/order_processor.go	Optimized relayer fee checks
XDCxlending/lendingstate/settle_balance.go	Optimized interest rate calculations
XDCx/tradingstate/settle_balance_test.go	Optimized test trade quantity setup
XDCx/order_processor.go	Optimized relayer fee checks

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[Copilot]

The variable name is inconsistent with the function signature. At line 592, v is being modified (using Sub which modifies the receiver), but this shadows the parameter v from line 584. The original code created a new big.Int with v = new(big.Int).Sub(v, big.NewInt(35)), but the updated code modifies the parameter directly with v.Sub(v, big.NewInt(35)). This changes the behavior by mutating the input parameter, which could cause unexpected side effects if the caller retains a reference to the parameter.

Suggested change

	v.Sub(v, big.NewInt(35))
	return v.Rsh(v, 1)
	vCopy := new(big.Int).Sub(v, big.NewInt(35))
	return vCopy.Rsh(vCopy, 1)

[Copilot]

The comment is incorrect. The code performs a left shift by 1, which multiplies by 2, not 3. The comment should say "2Y1Z1" instead of "3Y1Z1". Note that this appears to be a pre-existing issue (the original code also multiplied by 2), so it's not introduced by this PR, but it would be good to fix it.

Suggested change

	z3.Lsh(z3, 1) //3*Y1*Z1
	z3.Lsh(z3, 1) //2*Y1*Z1