/* Write a subroutine to multiply a 16-bit unsigned number 
 * in the r25:r24 register pair by an 8-bit number in r26.
 * return the answer in r4:r3:r2  
 * Remember that when you multiply two numbers the result is in the
 * the r1:r0 register pair.
 * Study the following multiplication example to see how it is done.
 *
 * Multiply
 *    r25:r24
 *    x   r26
 * ----------
 *    0:r3:r2  = r16*r18  first byte
 * + r1:r0     = r17*r18  second byte
 * --------
 *   r4:r3:r2  = (r1 + c):(r3 + r0):r2
 * 
 * For additional help read "Binary hardware multiplication in AVR Assembler"
 * at http://www.avr-asm-tutorial.net/avr_en/calc/HARDMULT.html
 *
 * Test your hardware multiplication 16-by-8-bit subroutine
 * by running the following test code.
 */
.INCLUDE <m328pdef.inc> 

muls16x8_24_test:
	ldi r25,HIGH(10000) ; upper 8 bits of multiplicand 
	ldi r24,LOW(10000)  ; lower 8 bits of multiplicand
	ldi r26,250         ; 8-bit constant multiplier 

muls16x8_24:
    push r15         ; save contents of registers modified by this subroutine
	in   r15, SREG
    push r24
	push r1
	push r0

    clr  r4
    mul  r24,r26     ; multiply LSB
	movw r3:r2,r1:r0 ; copy result to result register
	mul  r25,r26     ; multiply MSB
	add  r3,r0
    adc  r4,r1

	pop  r0
	pop  r1
	pop  r24
	out  SREG, r15
	pop  r15
	ret