An actual arbitrary-precision library would have a lot of loops with loops control and load and stores. Those aren't shown here. Those will dilute the effect of

An actual arbitrary-precision library would have a lot of loops with loops control and load and stores. Those aren't shown here. Those will dilute the effect of a few extra integer ALU instructions in RISC-V. Also, an high performance arbitrary-precision library would not fully propagate carries in every addition. Anywhere that a number of additions are being done in a row e.g. summing an array or series, or parts of a multiplication, you would want to use carry-save format for the intermediate results and fully propagate the carries only at the final step.