Samsung S3C2500B User Manual page 174

INSTRUCTION SET
Multiplication by 6
ADD
MOV
Multiply by 10 and add in extra number
ADD
ADD
General recursive method for Rb := Ra*C, C a constant:
1. If C even, say C = 2^n*D, D odd:
D=1:
D<>1:
MOV
2. If C MOD 4 = 1, say C = 2^n*D+1, D odd, n>1:
D=1:
D<>1:
ADD
3. If C MOD 4 = 3, say C = 2^n*D-1, D odd, n>1:
D=1:
D<>1:
RSB
This is not quite optimal, but close. An example of its non-optimality is multiply by 45 which is done by:
RSB
RSB
ADD
rather than by:
ADD
ADD
3-62
Ra,Ra,Ra,LSL #1
Ra,Ra,LSL#1
Ra,Ra,Ra,LSL#2
Ra,Rc,Ra,LSL#1
MOV Rb,Ra,LSL #n
{Rb := Ra*D}
Rb,Rb,LSL #n
ADD Rb,Ra,Ra,LSL #n
{Rb := Ra*D}
Rb,Ra,Rb,LSL #n
RSB Rb,Ra,Ra,LSL #n
{Rb := Ra*D}
Rb,Ra,Rb,LSL #n
Rb,Ra,Ra,LSL#2
Rb,Ra,Rb,LSL#2
Rb,Ra,Rb,LSL# 2
Rb,Ra,Ra,LSL#3
Rb,Rb,Rb,LSL#2
; Multiply by 3
; and then by 2
; Multiply by 5
; Multiply by 2 and add in next digit
; Multiply by 3
; Multiply by 4*3-1 = 11
; Multiply by 4*11+1 = 45
; Multiply by 9
; Multiply by 5*9 = 45
S3C2500B