Uasx And Usax - ST STM32F3 Series Programming Manual

PM0214
3.5.17

UASX and USAX

Add and Subtract with Exchange and Subtract and Add with Exchange.
Syntax
op{cond} {Rd}, Rn, Rm
Where:
• op is one of:
UASX: Add and subtract with exchange.
USAX: Subtract and add with exchange.
•
'cond' is an optional condition code (see
•
'Rd' is the destination register.
•
'Rn' 'Rm' are registers holding the first and second operands.
Operation
The UASX instruction:
1. Subtracts the top halfword of the second operand from the bottom halfword of the first
operand.
2. Writes the unsigned result from the subtraction to the bottom halfword of the
destination register.
3. Adds the top halfword of the first operand with bottom halfword of the second operand.
4. Writes the unsigned result of the addition to the top halfword of the destination register.
The USAX instruction:
1. Adds the bottom halfword of the first operand to the top halfword of the second
operand.
2. Writes the unsigned result of the addition to the bottom halfword of the destination
register.
3. Subtracts the bottom halfword of the second operand from the top halfword of the first
operand.
4. Writes the unsigned result from 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
UASX R0, R4, R5
USAX R7, R3, R2
; 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 R0
; and writes to bottom halfword of R0
; Subtracts top halfword of R2 from bottom halfword of R3
; and writes to bottom halfword of R7
; Adds top halfword of R3 to bottom halfword of R2 and
PM0214 Rev 10
The STM32 Cortex-M4 instruction set
Conditional execution on page 65).
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