Unsigned Bitfield Move copies any number of low-order bits from a source register into the same number of adjacent bits at any position in the destination register, with zeros in the upper and lower bits.
This instruction is used by the aliases LSL (immediate), LSR (immediate), UBFIZ, UBFX, UXTB, and UXTH.
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
sf | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | N | immr | imms | Rn | Rd | ||||||||||||||||||
opc |
integer d = UInt(Rd); integer n = UInt(Rn); integer datasize = if sf == '1' then 64 else 32; boolean inzero; boolean extend; integer R; integer S; bits(datasize) wmask; bits(datasize) tmask; case opc of when '00' inzero = TRUE; extend = TRUE; // SBFM when '01' inzero = FALSE; extend = FALSE; // BFM when '10' inzero = TRUE; extend = FALSE; // UBFM when '11' UnallocatedEncoding(); if sf == '1' && N != '1' then ReservedValue(); if sf == '0' && (N != '0' || immr<5> != '0' || imms<5> != '0') then ReservedValue(); R = UInt(immr); S = UInt(imms); (wmask, tmask) = DecodeBitMasks(N, imms, immr, FALSE);
<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. |
Alias | Of variant | Is preferred when |
---|---|---|
LSL (immediate) | 32-bit | imms != '011111' && imms + 1 == immr |
LSL (immediate) | 64-bit | imms != '111111' && imms + 1 == immr |
LSR (immediate) | 32-bit | imms == '011111' |
LSR (immediate) | 64-bit | imms == '111111' |
UBFIZ | UInt(imms) < UInt(immr) | |
UBFX | BFXPreferred(sf, opc<1>, imms, immr) | |
UXTB | immr == '000000' && imms == '000111' | |
UXTH | immr == '000000' && imms == '001111' |
bits(datasize) dst = if inzero then Zeros() else X[d]; bits(datasize) src = X[n]; // perform bitfield move on low bits bits(datasize) bot = (dst AND NOT(wmask)) OR (ROR(src, R) AND wmask); // determine extension bits (sign, zero or dest register) bits(datasize) top = if extend then Replicate(src<S>) else dst; // combine extension bits and result bits X[d] = (top AND NOT(tmask)) OR (bot AND tmask);
Internal version only: isa v27.02, AdvSIMD v26.0, pseudocode v34.2.2 ; Build timestamp: 2018-03-28T19:55
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