Example $7\mathrm{.}10$ Use right shifts to divide the unsigned number $65143$

by $4.$ Put the quotient in $Ax.$

Solution: To divide by $4,$ two right shifts are needed. Since the divi$-$

dend is unsigned, we use SHR$.$ The code is

Example $7\mathrm{.}11.$ If $AL$ contains $-15,$ give the decimal value of $L$ after

SAR AL$.,1$ is performed.

Solution: Execution of SAR AL$,1$ divides the number by $2$ and rounds

down. Dividing $-15$ by $2$ yields $-7\mathrm{.}5,$ and after rounding down we get $-8.$

In terms of the binary contents, we have $-15=11110001b.$ After shifting,

we have $11111000b=-8.$

Example $9\mathrm{.}7$ Write a procedure FACTORIAL that will compute N$!$ for a

positive integer $N.$ The procedure should receive $N$ in $Cx$ and return $N!$

in AX$.$ Suppose that overflow does not occur.

Solution: The definition of $N!$ is

$N1ifN=1$

$=N(N-1)(N-2)$dots$1ifN>1$

Here is an algorithm: $-$

It can be coded as follows:

Here CX$-$ is both loop counter and term; the LOOP instruction automatically

"decrements" it on$"$ each" it$$rati$$n through the loop. We assume the product

does not overflow $16$ bits.