Samsung YP-P10 User Manual download pdf (Page 191)

S3C2440A RISC MICROPROCESSOR THUMB INSTRUCTION SET

DIVISION BY A CONSTANT

Division by a constant can often be performed by a short fixed sequence of shifts, adds and subtracts.

Here is an example of a divide by 10 routine based on the algorithm in the ARM Cookbook in both Thumb and ARM

udiv10 ; Take argument in a1 returns quotient in a1,

; remainder in a2

LSR a3, a1, #2

LSR a3, a1, #4

LSR a3, a1, #8

LSR a3, a1, #16

ASL a3, a1, #2

udiv10 ; Take argument in a1 returns quotient in a1,

; remainder in a2

SUB a2, a1, #10

SUB a1, a1, a1, lsr #2

ADD a1, a1, a1, lsr #4

ADD a1, a1, a1, lsr #8

ADD a1, a1, a1, lsr #16

MOV a1, a1, lsr #3

ADD a3, a1, a1, asl #2

SUBS a2, a2, a3, asl #1

ADDPL a1, a1, #1

ADDMI a2, a2, #10

Samsung YP-P10 User Manual Page 191