Shsub16 And Shsub8 - ST STM32F3 Series Programming Manual

The STM32 Cortex-M4 instruction set
SHSAX
3.5.12

SHSUB16 and SHSUB8

Signed Halving Subtract 16 and Signed Halving Subtract 8
Syntax
op{cond}{Rd,} Rn, Rm
Where:
•
op is any of the following:
SHSUB16: Signed halving subtract 16
SHSUB8: Signed halving subtract 8
• 'cond' is an optional condition code (see
•
'Rd' is the destination register
• 'Rn' is the register holding the operand
•
'Rm' is the second operand register
Operation
Use these instructions to add 16-bit and 8-bit data and then to halve the result before writing
the result to the destination register:
The SHSUB16 instruction:
1. Subtracts each halfword of the second operand from the corresponding halfwords of
the first operand.
2. Shuffles the result by one bit to the right, halving the data.
3. Writes the halved halfword results in the destination register.
The SHSUBB8 instruction:
1. Subtracts each byte of the second operand from the corresponding byte of the first
operand,
2. Shuffles the result by one bit to the right, halving the data,
3. Writes the corresponding signed byte results in the destination register.
Restrictions
Do not use SP and do not use PC.
Condition flags
These instructions do not change the flags.
Examples
SHSUB16 R1, R0
SHSUB8
96/262
; R4 and writes halved result to bottom halfword of R7
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.
; Subtracts halfwords in R0 from corresponding halfword
; of R1 and writes to corresponding halfword of R1
R4, R0, R5 ; Subtracts bytes of R0 from corresponding byte in R5,
Conditional execution on page
PM0214 Rev 10
PM0214
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