TRN2

Transpose vectors (secondary)

This instruction reads corresponding odd-numbered vector elements from the two source SIMD&FP registers, places each result into consecutive elements of a vector, and writes the vector to the destination SIMD&FP register. Vector elements from the first source register are placed into even-numbered elements of the destination vector, starting at zero, while vector elements from the second source register are placed into odd-numbered elements of the destination vector.

By using this instruction with TRN1, a 2 x 2 matrix can be transposed.

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: Advanced SIMD

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	0			0						0	1	1	0	1	0
	Q							size			Rm						op					Rn					Rd

TRN2 <Vd>.<T>, <Vn>.<T>, <Vm>.<T>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
if size:Q == '110' then EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer esize = 8 << UInt(size);
constant integer datasize = 64 << UInt(Q);
constant integer elements = datasize DIV esize;
constant integer part = UInt(op);
constant integer pairs = elements DIV 2;

Operation

CheckFPAdvSIMDEnabled64();
constant bits(datasize) operand1 = V[n, datasize];
constant bits(datasize) operand2 = V[m, datasize];
bits(datasize) result;

for p = 0 to pairs-1
    Elem[result, 2*p+0, esize] = Elem[operand1, 2*p+part, esize];
    Elem[result, 2*p+1, esize] = Elem[operand2, 2*p+part, esize];

V[d, datasize] = result;

Explanations

<Vd>: Is the name of the SIMD&FP destination register, encoded in the "Rd" field.
<T>: <Vn>: Is the name of the first SIMD&FP source register, encoded in the "Rn" field.
<Vm>: Is the name of the second SIMD&FP source register, encoded in the "Rm" 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.