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FMSB

Floating-point fused multiply-subtract vectors (predicated), writing multiplicand [Zdn = Za + -Zdn * Zm].

Multiply the corresponding active floating-point elements of the first and second source vectors and subtract from elements of the third (addend) vector without intermediate rounding. Destructively place the results in the destination and first source (multiplicand) vector. Inactive elements in the destination vector register remain unmodified.

313029282726252423222120191817161514131211109876543210
01100101size1Za101PgZmZdn

SVE

FMSB <Zdn>.<T>, <Pg>/M, <Zm>.<T>, <Za>.<T>

if !HaveSVE() then UNDEFINED;
if size == '00' then UNDEFINED;
integer esize = 8 << UInt(size);
integer g = UInt(Pg);
integer dn = UInt(Zdn);
integer m = UInt(Zm);
integer a = UInt(Za);
boolean op1_neg = TRUE;
boolean op3_neg = FALSE;

Assembler Symbols

<Zdn>

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

<T> Is the size specifier, encoded in size:
size <T>
00 RESERVED
01 H
10 S
11 D
<Pg>

Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.

<Zm>

Is the name of the second source scalable vector register, encoded in the "Zm" field.

<Za>

Is the name of the third source scalable vector register, encoded in the "Za" field.

Operation

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(PL) mask = P[g];
bits(VL) operand1 = Z[dn];
bits(VL) operand2 = Z[m];
bits(VL) operand3 = Z[a];
bits(VL) result;

for e = 0 to elements-1
    bits(esize) element1 = Elem[operand1, e, esize];
    bits(esize) element2 = Elem[operand2, e, esize];
    bits(esize) element3 = Elem[operand3, e, esize];
    
    if ElemP[mask, e, esize] == '1' then
        if op1_neg then element1 = FPNeg(element1);
        if op3_neg then element3 = FPNeg(element3);
        Elem[result, e, esize] = FPMulAdd(element3, element1, element2, FPCR);
    else
        Elem[result, e, esize] = element1;

Z[dn] = result;

Operational information

This instruction might be immediately preceded in program order by a MOVPRFX instruction that conforms to all of the following requirements, otherwise the behavior of either or both instructions is unpredictable:

  • 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.
The MOVPRFX instructions that can be used with this instruction are as follows:
  • An unpredicated MOVPRFX instruction.
  • A predicated MOVPRFX instruction using the same governing predicate register and source element size as this instruction.
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