Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

 116

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

Signed Halving Add and Subtract with Exchange and Signed Halving Subtract and Add with Exchange.

Syntax

op{cond} {Rd}, Rn, Rm

where:

op

is any of:

SHASX Add and Subtract with Exchange and Halving.

SHSAX Subtract and Add with Exchange and Halving.

cond

Rd

is the destination register.

Rn, Rm

are registers holding the first and second operands.

Operation

The SHASX instruction:

1.

Adds the top halfword of the first operand with the bottom halfword of the second operand.

2.

Writes the halfword result of the addition to the top halfword of the destination register, shifted by one bit to the 
right causing a divide by two, or halving.

3.

Subtracts the top halfword of the second operand from the bottom highword of the first operand.

4.

Writes the halfword result of the division in the bottom halfword of the destination register, shifted by one bit to the 
right causing a divide by two, or halving.

The SHSAX instruction:

1.

Subtracts the bottom halfword of the second operand from the top highword of the first operand.

2.

Writes the halfword result of the addition to the bottom halfword of the destination register, shifted by one bit to the 
right causing a divide by two, or halving.

3.

Adds the bottom halfword of the first operand with the top halfword of the second operand.

4.

Writes the halfword result of the division in the top halfword of the destination register, shifted by one bit to the right 
causing a divide by two, or halving.

Restrictions

Do not use SP and do not use PC

Condition Flags

These instructions do not affect the condition code flags.

Examples

SHASX   R7, R4, R2  ; Adds top halfword of R4 to bottom halfword of R2

                    ; and writes halved result to top halfword of R7

                    ; Subtracts top halfword of R2 from bottom halfword of

                    ; R4 and writes halved result to bottom halfword of R7

SHSAX   R0, R3, R5  ; Subtracts bottom halfword of R5 from top halfword 

                    ; of R3 and writes halved result to top halfword of R0

                    ; Adds top halfword of R5 to bottom halfword of R3 and

                    ; writes halved result to bottom halfword of R0.