11.144 SXTAB

Sign extend Byte with Add, to extend an 8-bit value to a 32-bit value.

Syntax

SXTAB{cond} {Rd}, Rn, Rm {,rotation}

where:

cond

is an optional condition code.

Rd

is the destination register.

Rn

is the register holding the number to add.

Rm

is the register holding the value to extend.

rotation

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 rotation is omitted, no rotation is performed.

Operation

This instruction does the following:

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

  2. Extract bits[7:0] from the value obtained.

  3. Sign extend to 32 bits.

  4. Add the value from Rn.

Register restrictions

You cannot use PC for any register.

You can use SP in ARM instructions but this is deprecated in ARMv6T2 and above. You cannot use SP in Thumb instructions.

Condition flags

This instruction does not change the flags.

Architectures

This ARM instruction is available in ARMv6 and above.

This 32-bit Thumb instruction is available in ARMv6T2 and above. For the ARMv7-M architecture, it is only available in an ARMv7E-M implementation.

There is no 16-bit version of this instruction in Thumb.

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