v1.3.41

simgo v1.3.41 — Release Notes

Summary

Bugfix for v1.3.4: FeeAdjustedLe128 expansion used jet::add_128, which does not exist in
the Simplicity protocol. Replaced with jet::add_64 on u64 values after individually asserting
each product fits in 64 bits.

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Bug Fixed

jet::add_128 is not a valid Simplicity jet.

Simplicity arithmetic jets top out at 64-bit (add_64, full_add_64, etc.). The v1.3.4
expansion for FeeAdjustedLe128 attempted to sum two u128 products with a non-existent
add_128 jet, causing simc to reject the generated .shl with:

Jet 'add_128' does not exist

Fix

Instead of summing the u128 products directly, decompose each into (hi, lo) and assert both
hi words are zero before adding the lo words with add_64:

Before (broken):

let (_, fa_adj): (bool, u128) = jet::add_128(fa_t1, fa_t2);
let (fa_adj_hi, fa_adj_lo): (u64, u64) = <u128>::into(fa_adj);
assert!(jet::eq_64(fa_adj_hi, 0));

After (correct):

let (fa_t1_hi, fa_t1_lo): (u64, u64) = <u128>::into(fa_t1);
let (fa_t2_hi, fa_t2_lo): (u64, u64) = <u128>::into(fa_t2);
assert!(jet::eq_64(fa_t1_hi, 0));
assert!(jet::eq_64(fa_t2_hi, 0));
let (fa_carry, fa_adj_lo): (bool, u64) = jet::add_64(fa_t1_lo, fa_t2_lo);
unwrap_left::<()>(<bool>::into(fa_carry));

The semantics are identical: both products are asserted to fit in u64 (same overflow guard as
before), and the sum is asserted to not overflow u64. Valid for all practical pool sizes.

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Test Update

TestFeeAdjustedLe128Verify updated with two new assertions:

• Output contains jet::add_64(
• Output does not contain jet::add_128(

Full Changelog: v1.3.4...v1.3.41