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USHLL, USHLL2

Unsigned Shift Left Long (immediate). This instruction reads each vector element in the lower or upper half of the source SIMD&FP register, shifts the unsigned integer value left by the specified number of bits, places the result into a vector, and writes the vector to the destination SIMD&FP register. The destination vector elements are twice as long as the source vector elements.

The USHLL instruction extracts vector elements from the lower half of the source register, while the USHLL2 instruction extracts vector elements from the upper half of the source register.

Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

This instruction is used by the alias UXTL, UXTL2.

313029282726252423222120191817161514131211109876543210
0Q1011110!= 0000immb101001RnRd
Uimmh

Vector

USHLL{2} <Vd>.<Ta>, <Vn>.<Tb>, #<shift>

integer d = UInt(Rd);
integer n = UInt(Rn);

if immh == '0000' then SEE(asimdimm);
if immh<3> == '1' then UNDEFINED;
integer esize = 8 << HighestSetBit(immh);
integer datasize = 64;
integer part = UInt(Q);
integer elements = datasize DIV esize;

integer shift = UInt(immh:immb) - esize;
boolean unsigned = (U == '1');

Assembler Symbols

2 Is the second and upper half specifier. If present it causes the operation to be performed on the upper 64 bits of the registers holding the narrower elements, and is encoded in Q:
Q 2
0 [absent]
1 [present]
<Vd>

Is the name of the SIMD&FP destination register, encoded in the "Rd" field.

<Ta> Is an arrangement specifier, encoded in immh:
immh <Ta>
0000 SEE Advanced SIMD modified immediate
0001 8H
001x 4S
01xx 2D
1xxx RESERVED
<Vn>

Is the name of the SIMD&FP source register, encoded in the "Rn" field.

<Tb> Is an arrangement specifier, encoded in immh:Q:
immh Q <Tb>
0000 x SEE Advanced SIMD modified immediate
0001 0 8B
0001 1 16B
001x 0 4H
001x 1 8H
01xx 0 2S
01xx 1 4S
1xxx x RESERVED
<shift> Is the left shift amount, in the range 0 to the source element width in bits minus 1, encoded in immh:immb:
immh <shift>
0000 SEE Advanced SIMD modified immediate
0001 (UInt(immh:immb)-8)
001x (UInt(immh:immb)-16)
01xx (UInt(immh:immb)-32)
1xxx RESERVED

Alias Conditions

AliasIs preferred when
UXTL, UXTL2immb == '000' && BitCount(immh) == 1

Operation

CheckFPAdvSIMDEnabled64();
bits(datasize) operand = Vpart[n, part];
bits(datasize*2) result;
integer element;

for e = 0 to elements-1
    element = Int(Elem[operand, e, esize], unsigned) << shift;
    Elem[result, e, 2*esize] = element<2*esize-1:0>;

V[d] = result;

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.