PM0214 datasheet(134/245 Pages) STMICROELECTRONICS

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The STM32 Cortex-M4 instruction set

PM0214

134/245

DocID022708 Rev 4

3.8.2

SXT and UXT

Sign extend and Zero extend.

Syntax

op{cond} {Rd,} Rm {, ROR #n}

op{cond} {Rd}, Rm {, ROR #n}

where:

•

op’ is one of:

SXTB Sign extends an 8-bit value to a 32-bit value.

SXTH Sign extends a 16-bit value to a 32-bit value.

SXTB16 Sign extends two 8-bit values to two 16-bit values.

UXTB Zero extends an 8-bit value to a 32-bit value.

UXTH Zero extends a 16-bit value to a 32-bit value.

UXTB16 Zero extends two 8-bit values to two 16-bit values.

•

‘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.

SXTB16 extracts bits[7:0] and sign extends to 16 bits,

and extracts bits [23:16] and sign extends to 16 bits.

UXTB16 extracts bits[7:0] and zero extends to 16 bits,

and extracts bits [23:16] and zero extends to 16 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 ; Rotates R6 right by 16 bits, obtains bottom halfword

; of result, sign extends to 32 bits and writes to R4

UXTB

R3, R10

; Extracts lowest byte of value in R10, zero extends, and

; writes to R3.

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