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

Unsigned Halving Add and Subtract with Exchange.

UHSAX

Unsigned Halving Subtract and Add with Exchange.

cond

Is an optional condition code. See Conditional execution.

Rd

Is the destination register. If Rd is omitted, the destination register is Rn.

Rn

Is the first operand register.

Rm

Is the second operand register.

Operation

The UHASX instruction:

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

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

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

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

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

  6. Writes the halfword result of the subtraction in the bottom halfword of the destination register.

The UHSAX instruction:

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

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

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

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

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

  6. Writes the 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.
                        ; Adds top halfword of R5 to bottom halfword of R3 and 
                        ; writes halved result to bottom halfword of R0.
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