PM0214 datasheet(102/245 Pages) STMICROELECTRONICS

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The STM32 Cortex-M4 instruction set

PM0214

102/245

DocID022708 Rev 4

3.5.19

UHASX and UHSAX

Unsigned halving add and subtract with exchange and Unsigned halving subtract and add

with exchange.

Syntax

op{cond} {Rd}, Rn, Rm

where:

•

op is one of:

UHASX: Add and subtract with exchange and halving.

UHSAX: Subtract and add with exchange and halving.

•

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

•

‘Rd’ is the destination register

•

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

Operation

The UHASX instruction:

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

Shifts the result by one bit to the right causing a divide by two, or halving.

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

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

Shifts the result by one bit to the right causing a divide by two, or halving.

Writes halfword result of the division in the bottom halfword of the destination register.

The UHSAX instruction:

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

Shifts the result by one bit to the right causing a divide by two, or halving.

Writes halfword result of the subtraction in the top halfword of the destination register.

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

Shifts the result by one bit to the right causing a divide by two, or halving.

Writes halfword result of the addition to the bottom 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

UHASX

R7, R4, R2

; Adds top halfword of R4 with bottom halfword of R2

; and writes halved result to top halfword of R7

; Subtracts top halfword of R2 from bottom halfword of

; R7 and writes halved result to bottom halfword of R7

UHSAX

R0, R3, R5

; Subtracts bottom halfword of R5 from top halfword of

; R3 and writes halved result to top halfword of R0

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