ARM Cortex-M4 - SXTA and UXTA

The Cortex-M4 Instruction Set
ARM DUI 0553A Copyright © 2010 ARM. All rights reserved. 3-112
ID121610 Non-Confidential
3.8.3 SXTA and UXTA
Signed and Unsigned Extend and Add.
Syntax
op{cond} {Rd,} Rn, Rm {, ROR #n}
op{cond} {Rd,} Rn, Rm {, ROR #n}
where:
op Is one of:
SXTAB Sign extends an 8-bit value to a 32-bit value and add.
SXTAH Sign extends a 16-bit value to a 32-bit value and add.
SXTAB16 Sign extends two 8-bit values to two 16-bit values and add.
UXTAB Zero extends an 8-bit value to a 32-bit value and add.
UXTAH Zero extends a 16-bit value to a 32-bit value and add.
UXTAB16 Zero extends two 8-bit values to two 16-bit values and add.
cond Is an optional condition code, see Conditional execution on page 3-18.
Rd Specifies the destination register.
Rn Specifies the first operand register.
Rm Specifies the register holding the value to rotate and 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:
•
SXTAB extracts bits[7:0] from Rm and sign extends to 32 bits.
•
UXTAB extracts bits[7:0] from Rm and zero extends to 32 bits.
•
SXTAH extracts bits[15:0] from Rm and sign extends to 32 bits.
•
UXTAH extracts bits[15:0] from Rm and zero extends to 32 bits.
•
SXTAB16 extracts bits[7:0] from Rm and sign extends to 16 bits, and extracts bits
[23:16] from Rm and sign extends to 16 bits.
•
UXTAB16 extracts bits[7:0] from Rm and zero extends to 16 bits, and extracts bits
[23:16] from Rm and zero extends to 16 bits.
3. Adds the signed or zero extended value to the word or corresponding halfword of Rn and
writes the result in Rd.
Restrictions
Do not use SP and do not use PC.