fix a typo

[hczphn]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @hczphn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical logical flaw within the LogUpRangeProofTable implementation. The change ensures that a multiplication factor is correctly initialized, which is essential for subsequent bit shift operations to produce the intended values, thereby rectifying the range proof calculations.

Highlights

• Bug Fix: Corrected a logical error in the LogUpRangeProofTable implementation where a multiplication factor was incorrectly initialized.
• Calculation Correction: The mul_factor variable, used in bit shift operations for range proof calculations, was changed from an initial value of 0 to 1 to ensure accurate results.

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Changelog

• circuit-std-rs/src/logup.rs
  • Corrected the initialization of the mul_factor variable from 0 to 1 within the impl LogUpRangeProofTable block, specifically impacting the calculation of a_shift.

Activity

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[gemini-code-assist]

Code Review

This pull request fixes a bug in rangeproof_onechunk where mul_factor was incorrectly initialized to 0, causing the shift operation to have no effect. The change to initialize it to 1 is correct. I've added a suggestion to further improve the robustness of this code by explicitly typing variables to prevent potential integer overflows, making it consistent with similar logic in the rangeproof function.

[gemini-code-assist]

While initializing mul_factor to 1 is the correct fix, the code can be made more robust. The type of mul_factor is inferred by the compiler and could overflow if n is large (e.g., > 31). To prevent potential overflows and align with the implementation in the rangeproof function, it's better to explicitly type mul_factor as u128 and convert it to a circuit variable before the multiplication.

A similar issue exists for constant on line 428, which would also benefit from an explicit type like u128 to prevent potential overflows.

Suggested change

	let mut mul_factor = 1;
	mul_factor <<= n;
	let a_shift = builder.mul(constant, mul_factor);
	let mul_factor: u128 = 1 << n;
	let mul_factor_u256 = U256::new(mul_factor);
	let mul_factor_var = builder.constant(CircuitField::<C>::from_u256(mul_factor_u256));
	let a_shift = builder.mul(constant, mul_factor_var);