ST STM32F3 Series

PM0214 Rev 10 141/262
PM0214 The STM32 Cortex-M4 instruction set
261
3.9.3 SXT and UXT
Sign extend and Zero extend.
Syntax
SXTextend{cond} {Rd,} Rm {, ROR #n}
UXTextend{cond} {Rd}, Rm {, ROR #n}
Where:
• ‘extend’ is one of:
B: Extends an 8-bit value to a 32-bit value.
H: Extends a 16-bit value to a 32-bit value.
• ‘cond’ is an optional condition code, see Conditional execution on page 65.
• ‘Rd’ is the destination register.
• ‘Rm’ is the register holding the value to extend.
• ROR #n is one of:
ROR #8: Value from Rm is rotated right 8 bits.
ROR #16: Value from Rm is rotated right 16 bits.
ROR #24: Value from Rm is rotated right 24 bits.
If ROR #n is omitted, no rotation is performed.
Operation
These instructions do the following:
1. Rotate the value from Rm right by 0, 8, 16 or 24 bits.
2. Extract bits from the resulting value:
– SXTB extracts bits[7:0] and sign extends to 32 bits.
– UXTB extracts bits[7:0] and zero extends to 32 bits.
– SXTH extracts bits[15:0] and sign extends to 32 bits.
– UXTH extracts bits[15:0] and zero extends to 32 bits.
Restrictions
Do not use SP and do not use PC.
Condition flags
These instructions do not affect the flags.
Examples
SXTH R4, R6, ROR #16 ; Rotate R6 right by 16 bits, then obtain the lower
; halfword of the result and then sign extend to
; 32 bits and write the result to R4.
UXTB R3, R10 ; Extract lowest byte of the value in R10 and zero
; extend it, and write the result to R3