s3c2410a Samsung Semiconductor, Inc., s3c2410a Datasheet - Page 186

• Manufacturer Part Number: s3c2410a
• Description: 16/32-bit Risc Arm Microprocessor
• Manufacturer: Samsung Semiconductor, Inc.

THUMB INSTRUCTION SET
INSTRUCTION SET EXAMPLES
The following examples show ways in which the THUMB instructions may be used to generate small and efficient
code. Each example also shows the ARM equivalent so these may be compared.
MULTIPLICATION BY A CONSTANT USING SHIFTS AND ADDS
The following shows code to multiply by various constants using 1, 2 or 3 Thumb instructions alongside the ARM
equivalents. For other constants it is generally better to use the built-in MUL instruction rather than using a sequence
of 4 or more instructions.
1. Multiplication by 2^n (1,2,4,8,...)
2. Multiplication by 2^n+1 (3,5,9,17,...)
3. Multiplication by 2^n-1 (3,7,15,...)
4. Multiplication by -2^n (-2, -4, -8, ...)
5. Multiplication by -2^n-1 (-3, -7, -15, ...)
Multiplication by any C = {2^n+1, 2^n-1, -2^n or -2^n-1} * 2^n
Effectively this is any of the multiplications in 2 to 5 followed by a final shift. This allows the following additional
constants to be multiplied. 6, 10, 12, 14, 18, 20, 24, 28, 30, 34, 36, 40, 48, 56, 60, 62 .....
4-40
Thumb
LSL
LSL
ADD
LSL
SUB
LSL
MVN
LSL
SUB
(2..5)
LSL
ARM
Ra, Rb, LSL #n
Rt, Rb, #n
Ra, Rt, Rb
Rt, Rb, #n
Ra, Rt, Rb
Rt, Rb, #n
Ra, Rb, Rt
Ra, Rb, #n
Ra, Ra
Ra, Ra, #n
; MOV Ra, Rb, LSL #n
; ADD Ra, Rb, Rb, LSL #n
; RSB Ra, Rb, Rb, LSL #n
; MOV Ra, Rb, LSL #n
; RSB Ra, Ra, #0
; SUB Ra, Rb, Rb, LSL #n
; (2..5)
; MOV Ra, Ra, LSL #n
S3C2410A