SHL

Shift left (immediate)

This instruction reads each value from a vector, left shifts each result by an immediate value, writes the final result to a vector, and writes the vector to the destination SIMD&FP 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.

Encoding: Scalar

Variants: FEAT_AdvSIMD (ARMv8.0)

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
0	1	0	1	1	1	1	1	0	1	x	x	x				0	1	0	1	0	1
		U							immh				immb			opcode						Rn					Rd

SHL D<d>, D<n>, #UInt("immh:immb") - 64." class="text-blue-400 hover:text-yellow-300"><shift>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
if immh<3> != '1' then EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer esize = 8 << 3;
constant integer datasize = esize;
constant integer elements = 1;
constant integer shift = UInt(immh:immb) - esize;

Encoding: Vector

Variants: FEAT_AdvSIMD (ARMv8.0)

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
0		0	0	1	1	1	1	0	!= 0000							0	1	0	1	0	1
	Q	U							immh				immb			opcode						Rn					Rd

SHL <Vd>.<T>, <Vn>.<T>, #<shift>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
if immh == '0000' then SEE(asimdimm);
if immh<3>:Q == '10' then EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer esize = 8 << HighestSetBitNZ(immh);
constant integer datasize = 64 << UInt(Q);
constant integer elements = datasize DIV esize;
constant integer shift = UInt(immh:immb) - esize;

Operation

CheckFPAdvSIMDEnabled64();
constant bits(datasize) operand = V[n, datasize];
bits(datasize) result;

for e = 0 to elements-1
    Elem[result, e, esize] = LSL(Elem[operand, e, esize], shift);

V[d, datasize] = result;

Explanations

<d>: Is the number of the SIMD&FP destination register, encoded in the "Rd" field.
<n>: Is the number of the SIMD&FP source register, encoded in the "Rn" field.
<shift>: For the "Scalar" variant: is the left shift amount, in the range 0 to 63, encoded as UInt("immh:immb") - 64.
<shift>: <Vd>: Is the name of the SIMD&FP destination register, encoded in the "Rd" field.
<T>: <Vn>: Is the name of the SIMD&FP source register, encoded in the "Rn" field.

Operational Notes

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.