Floating-point fused multiply-subtract by indexed element
This instruction multiplies all floating-point elements within each 128-bit segment of the first source vector by the specified element in the corresponding second source vector segment. The products are then destructively subtracted without intermediate rounding from the corresponding elements of the addend and destination vector.
The elements within the second source vector are specified using an immediate index that selects the same element position within each 128-bit vector segment. The index range is from 0 to one less than the number of elements per 128-bit segment. This instruction is unpredicated.
It has encodings from 3 classes: Half-precision , Single-precision and Double-precision
| 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 | 0 | 0 | 1 | 0 | 0 | 0 | i3h | 1 | i3l | Zm | 0 | 0 | 0 | 0 | 0 | 1 | Zn | Zda | |||||||||||
| o2 | op | ||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 16; let index : integer = UInt(i3h::i3l); let n : integer = UInt(Zn); let m : integer = UInt(Zm); let da : integer = UInt(Zda); let op1_neg : boolean = TRUE; let op3_neg : boolean = FALSE;
| 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 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | i2 | Zm | 0 | 0 | 0 | 0 | 0 | 1 | Zn | Zda | |||||||||||
| size | o2 | op | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 32; let index : integer = UInt(i2); let n : integer = UInt(Zn); let m : integer = UInt(Zm); let da : integer = UInt(Zda); let op1_neg : boolean = TRUE; let op3_neg : boolean = FALSE;
| 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 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | i1 | Zm | 0 | 0 | 0 | 0 | 0 | 1 | Zn | Zda | |||||||||||
| size | o2 | op | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 64; let index : integer = UInt(i1); let n : integer = UInt(Zn); let m : integer = UInt(Zm); let da : integer = UInt(Zda); let op1_neg : boolean = TRUE; let op3_neg : boolean = FALSE;
| <Zda> |
Is the name of the third source and destination scalable vector register, encoded in the "Zda" field. |
| <Zn> |
Is the name of the first source scalable vector register, encoded in the "Zn" field. |
CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let elements : integer = VL DIV esize; let eltspersegment : integer = 128 DIV esize; let op1 : bits(VL) = Z{}(n); let op2 : bits(VL) = Z{}(m); var result : bits(VL) = Z{}(da); for e = 0 to elements-1 do let segmentbase : integer = e - (e MOD eltspersegment); let s : integer = segmentbase + index; let elem2 : bits(esize) = op2[s*:esize]; let elem1 : bits(esize) = (if op1_neg then FPNeg{esize}(op1[e*:esize], FPCR()) else op1[e*:esize]); let elem3 : bits(esize) = (if op3_neg then FPNeg{esize}(result[e*:esize], FPCR()) else result[e*:esize]); result[e*:esize] = FPMulAdd{esize}(elem3, elem1, elem2, FPCR()); end; Z{VL}(da) = result;
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:
2026-03_rel 2026-03-26 20:48:11
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