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SBCLB

Subtract with carry long (bottom).

Subtract the even-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.

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010001011sz0Zm110100ZnZda
T
if !HaveSVE2() then UNDEFINED;
integer esize = 32 << UInt(sz);
integer n = UInt(Zn);
integer m = UInt(Zm);
integer da = UInt(Zda);

Assembler Symbols

<Zda>

Is the name of the third source and destination scalable vector register, encoded in the "Zda" field.

<T> Is the size specifier, encoded in sz:
sz <T>
0 S
1 D
<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.

Operation

CheckSVEEnabled();
integer pairs = VL DIV (esize * 2);
bits(VL) operand = Z[n];
bits(VL) carries = Z[m];
bits(VL) result = Z[da];
 
for p = 0 to pairs-1
    bits(esize) element1 = Elem[result, 2*p + 0, esize];
    bits(esize) element2 = Elem[operand, 2*p + 0, esize];
    bit carry_in = Elem[carries, 2*p + 1, esize]<0>;

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

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

Z[da] = result;

Operational information

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 instruction must conform to all of the following requirements, otherwise the behavior of the MOVPRFX and this instruction is unpredictable:

  • The MOVPRFX instruction must be unpredicated.
  • The MOVPRFX instruction 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.