The STM32 Cortex-M4 instruction set PM0214
108/262 PM0214 Rev 10
3.5.24 USUB16 and USUB8
Unsigned Subtract 16 and Unsigned Subtract 8
Syntax
op{cond}{Rd,} Rn, Rm
Where:
• op is any of:
USUB16: Unsigned Subtract 16.
USUB8: Unsigned Subtract 8.
• ‘cond’ is an optional condition code (see Conditional execution on page 65)
• ‘Rd’ is the destination register
• ‘Rn’ is the register holding the operand
• ‘Rm’ is the second operand register
Operation
Use these instructions to subtract 16-bit and 8-bit data before writing the result to the
destination register:
The USUB16 instruction:
1. Subtracts each halfword from the second operand register from the corresponding
halfword of the first operand register.
2. Writes the unsigned result in the corresponding halfwords of the destination register.
The USUB8 instruction:
1. Subtracts each byte of the second operand register from the corresponding byte of the
first operand register.
2. Writes the unsigned byte result in the corresponding byte of the destination register.
Restrictions
Do not use either SP or PC.
Condition flags
These instructions do not change the flags.
Examples
USUB16 R1, R0 ; Subtracts halfwords in R0 from corresponding halfword of
; R1 and writes to corresponding halfword in R1
USUB8 R4, R0, R5 ; Subtracts bytes of R5 from corresponding byte in R0 and
; writes to the corresponding byte in R4.
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