PM0214 datasheet(139/245 Pages) STMICROELECTRONICS

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PM0214

The STM32 Cortex-M4 instruction set

244

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 64.

•

‘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:

Rotate the value from Rm right by 0, 8, 16 or 24 bits.

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

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