PM0214 datasheet(97/245 Pages) STMICROELECTRONICS

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PM0214

The STM32 Cortex-M4 instruction set

244

3.5.14

SASX and SSAX

Signed add and subtract with exchange and Signed subtract and add with exchange.

Syntax

op{cond} {Rd}, Rm, Rn

where:

•

op is any of:

SASX: Signed add and subtract with exchange.

SSAX: Signed subtract and add with exchange.

•

‘cond’ is an optional condition code (see Conditional execution on page 64)

•

‘Rd’ is the destination register

•

‘Rn’ ,‘Rm’ are the registers holding the first and second operands

Operation

The SASX instruction:

Adds the signed top halfword of the first operand with the signed bottom halfword of the

second operand.

Writes the signed result of the addition to the top halfword of the destination register.

Subtracts the signed bottom halfword of the second operand from the top signed

highword of the first operand.

Writes the signed result of the subtraction to the bottom halfword of the destination

The SSAX instruction:

Subtracts the signed bottom halfword of the second operand from the top signed

highword of the first operand.

Writes the signed result of the addition to the bottom halfword of the destination

Adds the signed top halfword of the first operand with the signed bottom halfword of the

second operand.

Writes the signed result of the subtraction to the top halfword of the destination register.

Restrictions

Do not use SP and do not use PC.

Condition flags

These instructions do not affect the condition code flags.

Examples

SASX R0, R4, R5

; Adds top halfword of R4 to bottom halfword of R5 and

; writes to top halfword of R0

; Subtracts bottom halfword of R5 from top halfword of R4

; and writes to bottom halfword of R0

SSAX R7, R3, R2

; Subtracts top halfword of R2 from bottom halfword of R3

; and writes to bottom halfword of R7

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