The whole chapter in one function
Four 64-bit operands, three operations, one expression. That is the finale, and blend3(p, q, r, s) shows the shape: it adds three 64-bit values, then ORs the sum with a fourth:
addc r4, r4, r6 # (p + q) low, carry
adde r0, r3, r5 # (p + q) high
addc r3, r8, r4 # (... + r) low, carry
adde r0, r7, r0 # (... + r) high -> sum in r0:r3
or r4, r10, r3 # (sum | s) low -- bitwise, no flag
or r3, r9, r0 # (sum | s) high
blr
Three stages, six instructions and the blr. The opening addc/adde build p + q, then the next pair folds in r, leaving the running sum spread across a scratch high word and a low word. From there the two ors mask in s, no flag crossing the halves. One thing to mind: the fourth argument s lands in r9:r10, so by now the operands sit nowhere near where they started.
Your target reuses this skeleton with two swaps. The middle pair borrows where blend3 carried, and the closing pair masks with a bitwise op that isn't or. Name each operator from its pair, and since every pair feeds the next, the r3:r4 value at the blr is the whole four-operand expression.
Your task
Write fuse_64, taking four u64s, to reproduce the assembly above.