SQDMULL, SQDMULL2 (vector)

Signed saturating doubling multiply long

This instruction multiplies corresponding vector elements in the lower or upper half of the two source SIMD&FP registers, doubles the results, places the final results in a vector, and writes the vector to the destination SIMD&FP register.

If overflow occurs with any of the results, those results are saturated. If saturation occurs, the cumulative saturation bit FPSR.QC is set.

The SQDMULL instruction extracts each source vector from the lower half of each source register. The SQDMULL2 instruction extracts each source vector from the upper half of each 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.

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	0			1						1	1	0	1	0	0
		U						size			Rm					opcode						Rn					Rd

SQDMULL <Va><d>, <Vb><n>, <Vb><m>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
if size == '00' || size == '11' 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 = esize;
constant integer elements = 1;
constant integer part = 0;

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	0			1						1	1	0	1	0	0
	Q	U						size			Rm					opcode						Rn					Rd

SQDMULL{2} <Vd>.<Ta>, <Vn>.<Tb>, <Vm>.<Tb>

Decoding algorithm

if !IsFeatureImplemented(FEAT_AdvSIMD) then EndOfDecode(Decode_UNDEF);
if size == '00' || size == '11' 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;
constant integer part = UInt(Q);
constant integer elements = datasize DIV esize;

Operation

CheckFPAdvSIMDEnabled64();
constant bits(datasize) operand1 = Vpart[n, part, datasize];
constant bits(datasize) operand2 = Vpart[m, part, datasize];
bits(2*datasize) result;
integer element1;
integer element2;
bits(2*esize) product;
boolean sat;

for e = 0 to elements-1
    element1 = SInt(Elem[operand1, e, esize]);
    element2 = SInt(Elem[operand2, e, esize]);
    (product, sat) = SignedSatQ(2 * element1 * element2, 2 * esize);
    Elem[result, e, 2*esize] = product;
    if sat then FPSR.QC = '1';

V[d, 2*datasize] = result;

Explanations

<Va>: <d>: Is the number of the SIMD&FP destination register, encoded in the "Rd" field.
<Vb>: <n>: Is the number of the first SIMD&FP source register, encoded in the "Rn" field.
<m>: Is the number of the second SIMD&FP source register, encoded in the "Rm" field.
2: <Vd>: Is the name of the SIMD&FP destination register, encoded in the "Rd" field.
<Ta>: <Vn>: Is the name of the first SIMD&FP source register, encoded in the "Rn" field.
<Tb>: <Vm>: Is the name of the second SIMD&FP source register, encoded in the "Rm" field.