Change for a twenty

A customer pays with a twenty-dollar bill, 2000 cents. The starter reads the price in cents, from 0 to 2000. Work out the change, then split it into as few coins as possible: as many quarters (25 cents) as fit, then dimes (10), then nickels (5), then pennies (1). Leave the results in change_r, quarters_r, dimes_r, nickels_r and pennies_r; the starter prints them.

AArch64 has no remainder instruction. sdivSigned divide; divide-by-zero writes 0. gives how many whole times one number fits in another, and msubRd = Ra - Rn * Rm. multiplies two registers and subtracts the product from a third, which is exactly the leftover:

sdiv    w9, w12, w10        // w9 = w12 / w10, fraction dropped
msub    w13, w9, w10, w12   // w13 = w12 - w9 * w10, the remainder

For a price of 1541 the change is 459 cents: 18 quarters make 450, which leaves 9 cents, and 9 cents is 0 dimes, 1 nickel and 4 pennies.

What is checked

• with input 1541 the output is change in cents: 459, then 25c x 18, 10c x 0, 5c x 1 and 1c x 4, one per line
• the program exits cleanly
• the leftovers come from msubRd = Ra - Rn * Rm.
• the program also runs on prices you do not see, including one that needs no change at all and one that needs every kind of coin