sbfm
Signed Bitfield Move
Extracts/Inserts bitfield with sign extension.
Pseudocode Operation
width ← imms - immr + 1
if imms >= immr then
extracted ← ROR(Wn, immr)[width-1:0]
Wd ← SignExtend(extracted, width)
else
extracted ← ROR(Wn, immr)[width-1:0]
Wd ← SignExtend(extracted, width)
N ← unchanged
Z ← unchanged
C ← unchanged
V ← unchangedExample
Encoding
Operands
-
Wd
Destination 32-bit integer register -
Wn
First source / base 32-bit integer register -
immr
Rotate -
imms
Size
Related
More in Base
Reference
Instruction Forms
| Encoding | Instruction | ISA | Bit pattern | ||
|---|---|---|---|---|---|
| 0x13000000 | SBFM <Wd>, <Wn>, #<immr>, #<imms> | A64 | 0 | 00 | 100110 | 0 | immr | imms | Rn | Rd | ||
| 0x93400000 | SBFM <Xd>, <Xn>, #<immr>, #<imms> | A64 | 1 | 00 | 100110 | 1 | immr | imms | Rn | Rd |
Description
Signed Bitfield Move is usually accessed via one of its aliases, which are always preferred for disassembly. If <imms> is greater than or equal to <immr>, this copies a bitfield of (<imms>-<immr>+1) bits starting from bit position <immr> in the source register to the least significant bits of the destination register. If <imms> is less than <immr>, this copies a bitfield of (<imms>+1) bits from the least significant bits of the source register to bit position (regsize-<immr>) of the destination register, where regsize is the destination register size of 32 or 64 bits. In both cases the destination bits below the bitfield are set to zero, and the bits above the bitfield are set to a copy of the most significant bit of the bitfield.
Operation
bits(datasize) src = X[n, datasize]; // perform bitfield move on low bits bits(datasize) bot = ROR(src, r) AND wmask; // determine extension bits (sign, zero or dest register) bits(datasize) top = Replicate(src<s>, datasize); // combine extension bits and result bits X[d, datasize] = (top AND NOT(tmask)) OR (bot AND tmask);