fix: Assert the ammAssetOut denominator is non-zero - #7959
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ammAssetOut divides by (t1 * f - 1) in both the pre-fixAMMv1_3 and current paths without recording why the denominator is safe. Hoist it into a named local and assert it, so the contract lives with the code and a future change that widens the input ranges trips in Debug. The invariant holds because f = tfee / kAuctionSlotFeeScaleFactor is bounded by kTradingFeeThreshold (0.01) and t1 <= 1, putting denom in [-1, -0.99]. The tighter 0 < t1 <= 1 is deliberately not asserted: it is violable for a sole LP without fixAMMv1_1 and t1 == 0 is reachable pre-fixAMMv1_3, which would crash Debug builds on real ledger data. Fixes XRPLF#6661
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August 5, 2026 18:16
ammAssetOut divides by (t1 * f - 1) in both the pre-fixAMMv1_3 and current paths without recording why the denominator is safe. Hoist it into a named local and assert it, so the contract lives with the code and a future change that widens the input ranges trips in Debug. The invariant holds because f = tfee / kAuctionSlotFeeScaleFactor is bounded by kTradingFeeThreshold (0.01) and t1 <= 1, putting denom in [-1, -0.99]. The tighter 0 < t1 <= 1 is deliberately not asserted: it is violable for a sole LP without fixAMMv1_1 and t1 == 0 is reachable pre-fixAMMv1_3, which would crash Debug builds on real ledger data. Fixes XRPLF#6661
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Closes #6661.
Adds the defensive
XRPL_ASSERTrequested in the issue.Two notes on the issue as filed:
src/libxrpl/ledger/helpers/AMMHelpers.cpp, notsrc/libxrpl/tx/transactors/dex/.fixAMMv1_3path but not the legacy branch. Hoisting intodenomcovers both with a single assert.Uses
beast::kZerorather than the issue'sNumber{0}— both compile, butbeast::kZerois the existing idiom in this file and in the sibling denominator guard inAMMWithdraw::singleWithdrawEPrice.The tighter
0 < t1 <= 1invariant is deliberately not asserted. It is genuinely violable in production —t1can exceed 1 marginally for a sole LP withoutfixAMMv1_1, andt1 == 0is rle pre-fixAMMv1_3insingleWithdrawTokens— so asserting it would crash Debug builds on real ledger data, contrary to CONTRIBUTING.md's rule on contracts violable by external conditions.Release behavior is unchanged;
XRPL_ASSERTcompiles out, and hoisting the subexpression is value-identical (no rounding-mode guard is active at that point).🤖 Generated with Claude Code