Sxt And Uxt - ST STM32F4 Series Programming Manual

The STM32 Cortex-M4 instruction set
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
•
'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:
–
–
–
–
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
UXTB R3, R10
140/260
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.
; 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.
; Extract lowest byte of the value in R10 and zero
; extend it, and write the result to R3
DocID022708 Rev 6
Conditional execution on page
PM0214
64.