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BFI

Bitfield Insert copies a bitfield of <width> bits from the least significant bits of the source register to bit position <lsb> of the destination register, leaving the other destination bits unchanged.

This is an alias of BFM. This means:

  • The encodings in this description are named to match the encodings of BFM.
  • The description of BFM gives the operational pseudocode for this instruction.

313029282726252423222120191817161514131211109876543210
sf01100110Nimmrimms!= 11111Rd
opcRn

32-bit (sf == 0 && N == 0)

BFI <Wd>, <Wn>, #<lsb>, #<width>

is equivalent to

BFM <Wd>, <Wn>, #(-<lsb> MOD 32), #(<width>-1)

and is the preferred disassembly when UInt(imms) < UInt(immr).

64-bit (sf == 1 && N == 1)

BFI <Xd>, <Xn>, #<lsb>, #<width>

is equivalent to

BFM <Xd>, <Xn>, #(-<lsb> MOD 64), #(<width>-1)

and is the preferred disassembly when UInt(imms) < UInt(immr).

Assembler Symbols

<Wd>

Is the 32-bit name of the general-purpose destination register, encoded in the "Rd" field.

<Wn>

Is the 32-bit name of the general-purpose source register, encoded in the "Rn" field.

<Xd>

Is the 64-bit name of the general-purpose destination register, encoded in the "Rd" field.

<Xn>

Is the 64-bit name of the general-purpose source register, encoded in the "Rn" field.

<lsb>

For the 32-bit variant: is the bit number of the lsb of the destination bitfield, in the range 0 to 31.

For the 64-bit variant: is the bit number of the lsb of the destination bitfield, in the range 0 to 63.

<width>

For the 32-bit variant: is the width of the bitfield, in the range 1 to 32-<lsb>.

For the 64-bit variant: is the width of the bitfield, in the range 1 to 64-<lsb>.

Operation

The description of BFM gives the operational pseudocode for this instruction.

Operational information

If PSTATE.DIT is 1:

  • The execution time of this instruction is independent of:
    • The values of the data supplied in any of its registers.
    • The values of the NZCV flags.
  • The response of this instruction to asynchronous exceptions does not vary based on:
    • The values of the data supplied in any of its registers.
    • The values of the NZCV flags.
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