SBCLT

Subtract with carry long (top)

Subtract the odd-numbered elements of the first source vector and the inverted 1-bit carry from the least-significant bit of the odd-numbered elements of the second source vector from the even-numbered elements of the destination and accumulator vector. The 1-bit carry output is placed in the corresponding odd-numbered element of the destination vector.

Encoding: SVE2

Variants: FEAT_SVE2 || FEAT_SME (FEAT_SVE2 || FEAT_SME)

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	0	0	1	0	1	1		0						1	1	0	1	0	1
									sz		Zm										T	Zn					Zda

SBCLT <Zda>.<T>, <Zn>.<T>, <Zm>.<T>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE2) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
constant integer esize = 32 << UInt(sz);
constant integer n = UInt(Zn);
constant integer m = UInt(Zm);
constant integer da = UInt(Zda);

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer pairs = VL DIV (esize * 2);
constant bits(VL) operand = Z[n, VL];
constant bits(VL) carries = Z[m, VL];
bits(VL) result = Z[da, VL];

for p = 0 to pairs-1
    constant bits(esize) element1 = Elem[result, 2*p + 0, esize];
    constant bits(esize) element2 = Elem[operand, 2*p + 1, esize];
    constant bit carry_in = Elem[carries, 2*p + 1, esize]<0>;

    constant (res, nzcv) = AddWithCarry(element1, NOT(element2), carry_in);
    constant bit carry_out = nzcv<1>;

    Elem[result, 2*p + 0, esize] = res;
    Elem[result, 2*p + 1, esize] = ZeroExtend(carry_out, esize);

Z[da, VL] = result;

Explanations

<Zda>: Is the name of the third source and destination scalable vector register, encoded in the "Zda" field.
<T>: <Zn>: Is the name of the first source scalable vector register, encoded in the "Zn" field.
<Zm>: Is the name of the second source scalable vector register, encoded in the "Zm" 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.

This instruction might be immediately preceded in program order by a MOVPRFX instruction. The MOVPRFX must conform to all of the following requirements, otherwise the behavior of the MOVPRFX and this instruction is CONSTRAINED UNPREDICTABLE:

• The MOVPRFX must be unpredicated.
• The MOVPRFX must specify the same destination register as this instruction.
• The destination register must not refer to architectural register state referenced by any other source operand register of this instruction.