AMD Typewriter x86 사용자 설명서

22007E/0—November 1999

In the opt_utilities directory of the AMD documentation
CDROM, run sdiv.exe in a DOS window to find the fastest code
for signed division by a constant. The utility displays the code
after the user enters a signed constant divisor. Type “sdiv >
example.out” to output the code to a file.

In the opt_utilities directory of the AMD documentation
CDROM, run udiv.exe in a DOS window to find the fastest code
for unsigned division by a constant. The utility displays the code
after the user enters an unsigned constant divisor. Type “udiv >
example.out” to output the code to a file.

The following code shows an unsigned division using a constant
value multiplier.

;In:

d = divisor, 1 <= d < 2^31, odd d

;Out: a = algorithm
;

m = multiplier

;

s = shift factor

;algorithm 0
MOV

EDX, dividend

MOV

EAX, m

MUL

EDX

SHR

EDX, s   ;EDX=quotient

;algorithm 1
MOV

EDX, dividend

MOV

EAX, m

MUL

EDX

ADD

EAX, m

ADC

EDX, 0

SHR

EDX, s   ;EDX=quotient

The derivation for the algorithm (a), multiplier (m), and shift
count (s), is found in the section “Unsigned Derivation for
Algorithm, Multiplier, and Shift Factor” on page 93.

For divisors 2

31

 <= d < 2

32

, the possible quotient values are

either 0 or 1. This makes it easy to establish the quotient by
simple comparison of the dividend and divisor. In cases where
the dividend needs to be preserved, example 1 below is
recommended.