[PERF] Build Zero-Memory Allocation SHA2-256 Precompile Caller in Yul

[mijinummi]

Labels: medium-difficulty, yul, cryptography, gasguard
Difficulty: Medium
Module: contracts/crypto/

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🧠 Concept

Create an inline Yul assembly helper for invoking the SHA2-256 precompile (address 0x02) directly from calldata without staging payload bytes in memory.

⚠️ Problem

Using high-level sha256(bytes) copies calldata payloads into temporary memory buffers before triggering the precompile call.

📁 Implementation Scope

• contracts/crypto/YulSHA256.sol
• test/crypto/YulSHA256.test.ts

🛠️ Requirements

1. Pass input calldata ranges directly to precompile address 0x02 via Yul staticcall.
2. Write precompile output directly to scratch space (0x00) and return the resulting digest.

🎯 Acceptance Criteria

• Computes SHA2-256 hashes without dynamic memory expansion.
• Matches standard sha256() outputs across all input sizes.