Qadd And Qsub - ST STM32F4 Series Programming Manual

PM0214
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
•
'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
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
To read the state of the Q flag, use the MRS instruction, see
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
QADD8
QSUB16
n–1
R7, R4, R2 ; Adds halfwords of R4 with corresponding halfword of
; R2, saturates to 16 bits and writes to corresponding
; halfword of R7
R3, R1, R6 ; Adds bytes of R1 to corresponding bytes of R6,saturates
; to 8 bits and writes to corresponding byte of R3
R4, R2, R3 ; Subtracts halfwords of R3 from corresponding halfword
DocID022708 Rev 6
The STM32 Cortex-M4 instruction set
Conditional execution on page
n–1
≤ x ≤ 2 -1, where x is given by the number of bits applied in
64)
MSR on page 186.
MRS on page 185.
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