Uniswap V3 math: complete dex/v3.zig (tick math, sqrtPriceX96 swaps)

[koko1123]

Motivation

dex/v3.zig and dex/router.zig are stubs while V2 math is complete and benchmarked (24ns getAmountOut). V3 concentrated-liquidity math is what searchers actually need in 2026, and a limb-native Zig implementation would extend the existing 'beats Rust on DEX math' story. Complements #15 (router ABI decoding).

Scope

• Tick <-> sqrtPriceX96 conversions (getSqrtRatioAtTick / getTickAtSqrtRatio, Q64.96 fixed point)
• swap-within-tick amount math (SwapMath.computeSwapStep equivalent)
• liquidity math helpers (getAmount0/1Delta)
• Bench entries comparing against the uniswap-v3 reference vectors

Pointers

u256 limb arithmetic in uint256.zig (mulDiv already exists and is benchmarked at 18ns); validate against the canonical TickMath test vectors from the Uniswap v3-core repo.

[koko1123]

Closing as already implemented. On review, src/dex/v3.zig (786 lines) already provides the full V3 math surface this issue asked for: getSqrtRatioAtTick / getTickAtSqrtRatio (TickMath with the canonical magic constants), getAmount0Delta / getAmount1Delta, getNextSqrtPriceFromInput/Output, computeSwapStep, and simulateSwap. It has 21 unit tests including boundary checks against the Uniswap reference values (MIN_SQRT_RATIO, MAX_SQRT_RATIO, Q96), is documented in docs/dex-math.mdx, benchmarked (dex_v3_tick_to_price, dex_v3_swap_step), and exported as eth.dex_v3. dex/router.zig likewise implements multi-hop V2/V3 quoting. This issue was filed in error against an outdated 'stub' assumption. If gaps remain (e.g. additional reference-vector coverage), please open a focused follow-up.