ST STM32H7 Series User Manual

The STM32 Cortex-M4 instruction set PM0214
128/262 PM0214 Rev 9
3.7.3 QADD and QSUB
Saturating Add and Saturating Subtract, signed.
Syntax
op{cond} {Rd}, Rn, Rm
op{cond} {Rd}, Rn, Rm
Where:
• op’ is one of:
QADD: Saturating 32-bit add.
QADD8: Saturating four 8-bit integer additions.
QADD16: Saturating two 16-bit integer additions.
QSUB: Saturating 32-bit subtraction.
QSUB8: Saturating four 8-bit integer subtraction.
QSUB16: Saturating two 16-bit integer subtraction.
• ‘cond’ is an optional condition code (see Conditional execution on page 65)
• ‘Rd’ is the destination register.
• ‘Rn, Rm’ are registers holding the first and second operands.
Operation
These instructions add or subtract two, four or eight values from the first and second
operands and then write a signed saturated value in the destination register.
The QADD and QSUB instructions apply the specified add or subtract, and then saturate the
result to the signed range -2
n–1
≤ x ≤ 2
n–1
-1, where x is given by the number of bits applied in
the instruction, 32, 16 or 8.
If the returned result is different from the value to be saturated, it is called saturation. If
saturation occurs, the QADD and QSUB instructions set the APSR Q flag to 1. Otherwise, Q
flag is unchanged. The 8-bit and 16-bit QADD and QSUB instructions always leave Q flag
unchanged.
To clear the Q flag to 0, you must use the MSR instruction, see MSR on page 187.
To read the state of the Q flag, use the MRS instruction, see MRS on page 186.
Restrictions
Do not use SP and do not use PC.
Condition flags
These instructions do not affect the condition code flags.
If saturation occurs, these instructions set the Q flag to 1.
Examples
QADD16 R7, R4, R2 ; Adds halfwords of R4 with corresponding halfword of
; R2, saturates to 16 bits and writes to corresponding
; halfword of R7
QADD8 R3, R1, R6 ; Adds bytes of R1 to corresponding bytes of R6,saturates
; to 8 bits and writes to corresponding byte of R3
QSUB16 R4, R2, R3 ; Subtracts halfwords of R3 from corresponding halfword

ST STM32H7 Series Specifications

General

Brand	ST
Model	STM32H7 Series
Category	Computer Hardware
Language	English