ARM VERSION 1.2 - Manual (Page 218)

Thumb Instruction Reference
5-24 Copyright © 2000, 2001 ARM Limited. All rights reserved. ARM DUI 0068B
5.3.2 ASR, LSL, LSR, and ROR
Shift and rotate operations. These instructions can use a value contained in a register, or
an immediate shift value.
Syntax
op Rd, Rs
op Rd, Rm, #expr
where:
op is one of:
ASR Arithmetic Shift Right. Register contents are treated as two’s
complement signed integers. The sign bit is copied into
vacated bits.
LSL Logical Shift Left. Vacated bits are cleared.
LSR Logical Shift Right. Vacated bits are cleared.
ROR Rotate Right. Bits moved out of the right-hand end of the
register are rotated back into the left-hand end.
Note
ROR can only be used with a register-controlled shift.
Rd is the destination register. It is also the source register for
register-controlled shifts.
Rd must be in the range r0 - r7 .
Rs is the register containing the shift value for register-controlled shifts. Rm
must be in the range r0 - r7 .
Rm is the source register for immediate shifts. Rm must be in the range r0 - r7 .
expr is the immediate shift value. It is an expression evaluating (at assembly
time) to an integer in the range:
• 0-31 if op is LSL
• 1-32 otherwise.