UBFX
Unsigned Bit Field Extract
Unsigned Bit Field Extract extracts any number of adjacent bits at any position from a register, zero-extends them to 32 bits, and writes the result to the destination register.
For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.
If CPSR.DIT is 1, this instruction has passed its condition execution check, and does not use R15 as either its source or destination:
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.
It has encodings from the following instruction sets:
A32 (
A1
)
and
T32 (
T1
)
.
!= 1111
0
1
1
1
1
1
1
1
0
1
UBFX{<c>}{<q>} <Rd>, <Rn>, #<lsb>, #<width>
d = UInt(Rd); n = UInt(Rn);
lsbit = UInt(lsb); widthminus1 = UInt(widthm1);
msbit = lsbit + widthminus1;
if d == 15 || n == 15 then UNPREDICTABLE;
if msbit > 31 then UNPREDICTABLE;
msbit > 31
1
1
1
1
0
(0)
1
1
1
1
0
0
0
(0)
UBFX{<c>}{<q>} <Rd>, <Rn>, #<lsb>, #<width>
d = UInt(Rd); n = UInt(Rn);
lsbit = UInt(imm3:imm2); widthminus1 = UInt(widthm1);
msbit = lsbit + widthminus1;
if d == 15 || n == 15 then UNPREDICTABLE; // Armv8-A removes UNPREDICTABLE for R13
if msbit > 31 then UNPREDICTABLE;
msbit > 31
<c>
See Standard assembler syntax fields.
<q>
See Standard assembler syntax fields.
<Rd>
Is the general-purpose destination register, encoded in the "Rd" field.
<Rn>
Is the general-purpose source register, encoded in the "Rn" field.
<lsb>
For encoding A1: is the bit number of the least significant bit in the field, in the range 0 to 31, encoded in the "lsb" field.
<lsb>
For encoding T1: is the bit number of the least significant bit in the field, in the range 0 to 31, encoded in the "imm3:imm2" field.
<width>
Is the width of the field, in the range 1 to 32-<lsb>, encoded in the "widthm1" field as <width>-1.
if ConditionPassed() then
EncodingSpecificOperations();
R[d] = ZeroExtend(R[n]<msbit:lsbit>, 32);