SQRDMLAH (by element)

Signed saturating rounding doubling multiply accumulate returning high half (by element)

This instruction multiplies the vector elements of the first source SIMD&FP register with the value of a vector element of the second source SIMD&FP register without saturating the multiply results, doubles the results, and accumulates the most significant half of the final results with the vector elements of the destination SIMD&FP register. The results are rounded.

If any of the results overflow, they are saturated. The cumulative saturation bit, FPSR.QC, is set if saturation occurs.

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_RDM (ARMv8.1)

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	1	1	1	1	1	1									1	1	0	1		0
		U						size		L	M	Rm						S		H		Rn					Rd

SQRDMLAH <V><d>, <V><n>, <Vm>.<Ts>[<index>]

Decoding algorithm

if !IsFeatureImplemented(FEAT_RDM) then EndOfDecode(Decode_UNDEF);
constant integer idxdsize = 64 << UInt(H);
integer index;
bit Rmhi;

case size of
    when '01' index = UInt(H:L:M); Rmhi = '0';
    when '10' index = UInt(H:L); Rmhi = M;
    otherwise EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rmhi:Rm);
constant integer esize = 8 << UInt(size);
constant integer datasize = esize;
constant integer elements = 1;

constant boolean rounding = TRUE;

Encoding: Vector

Variants: FEAT_RDM (ARMv8.1)

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	1	0	1		0
	Q	U						size		L	M	Rm						S		H		Rn					Rd

SQRDMLAH <Vd>.<T>, <Vn>.<T>, <Vm>.<Ts>[<index>]

Decoding algorithm

if !IsFeatureImplemented(FEAT_RDM) then EndOfDecode(Decode_UNDEF);
constant integer idxdsize = 64 << UInt(H);
integer index;
bit Rmhi;

case size of
    when '01' index = UInt(H:L:M); Rmhi = '0';
    when '10' index = UInt(H:L); Rmhi = M;
    otherwise EndOfDecode(Decode_UNDEF);

constant integer d = UInt(Rd);
constant integer n = UInt(Rn);
constant integer m = UInt(Rmhi:Rm);
constant integer esize = 8 << UInt(size);
constant integer datasize = 64 << UInt(Q);
constant integer elements = datasize DIV esize;

constant boolean rounding = TRUE;

Operation

CheckFPAdvSIMDEnabled64();
constant bits(datasize) operand1 = V[n, datasize];
constant bits(idxdsize) operand2 = V[m, idxdsize];
constant bits(datasize) operand3 = V[d, datasize];
bits(datasize) result;
integer element1;
integer element2;
integer element3;
integer accum;
boolean sat;

element2 = SInt(Elem[operand2, index, esize]);
for e = 0 to elements-1
    element1 = SInt(Elem[operand1, e, esize]);
    element3 = SInt(Elem[operand3, e, esize]);
    accum = (element3 << esize) + 2 * (element1 * element2);
    accum = RShr(accum, esize, rounding);
    (Elem[result, e, esize], sat) = SignedSatQ(accum, esize);
    if sat then FPSR.QC = '1';

V[d, datasize] = result;

Explanations

<V>: <d>: Is the number of the SIMD&FP destination register, encoded in the "Rd" field.
<n>: Is the number of the first SIMD&FP source register, encoded in the "Rn" field.
<Vm>: <Ts>: <index>: <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.

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.