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

 117

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

Signed Halving Subtract 16 and Signed Halving Subtract 8

Syntax

op{cond}{Rd,} Rn, Rm

where:

op

is any of:

SHSUB16 Signed Halving Subtract 16.

SHSUB8 Signed Halving Subtract 8.

cond

Rd

is the destination register.

Rn

is the first operand register.

Rm

is the second operand register.

Operation

Use these instructions to add 16-bit and 8-bit data and then to halve the result before writing the result to the destination
register:

The SHSUB16 instruction: 

1.

Subtracts each halfword of the second operand from the corresponding halfwords of the first operand.

2.

Shuffles the result by one bit to the right, halving the data.

3.

Writes the halved halfword results in the destination register.

The SHSUBB8 instruction: 

1.

Subtracts each byte of the second operand from the corresponding byte of the first operand,

2.

Shuffles the result by one bit to the right, halving the data,

3.

Writes the corresponding signed byte results in the destination register.

Restrictions

Do not use SP and do not use PC

Condition Flags

These instructions do not change the flags.

Examples

SHSUB16 R1, R0     ; Subtracts halfwords in R0 from corresponding halfword

                   ; of R1 and writes to corresponding halfword of R1

SHSUB8  R4, R0, R5 ; Subtracts bytes of R0 from corresponding byte in R5,

                   ; and writes to corresponding byte in R4.