BFDOT (indexed)

BFloat16 floating-point indexed dot product

The BFloat16 floating-point (BF16) indexed dot product instruction computes the dot product of a pair of BF16 values held in each 32-bit element of the first source vector multiplied by a pair of BF16 values in an indexed 32-bit element of the second source vector, and then destructively adds the single-precision dot product to the corresponding single-precision element of the destination vector.

The BF16 pairs within the second source vector are specified using an immediate index which selects the same BF16 pair position within each 128-bit vector segment. The index range is from 0 to 3. This instruction is unpredicated.

All floating-point calculations performed by this instruction are performed with the following behaviors, irrespective of the value in FPCR:

* Uses the non-IEEE 754 Round-to-Odd mode, which forces bit 0 of an inexact result to 1, and rounds an overflow to an appropriately signed Infinity.

* The cumulative FPSR exception bits (IDC, IXC, UFC, OFC, DZC and IOC) are not modified.

* Trapped floating-point exceptions are disabled, as if the FPCR trap enable bits (IDE, IXE, UFE, OFE, DZE and IOE) are all zero.

* Denormalized inputs and results are flushed to zero, as if FPCR.FZ == 1.

* Only the Default NaN is generated, as if FPCR.DN == 1.

ID_AA64ZFR0_EL1.BF16 indicates whether this instruction is implemented.

SVE
(FEAT_BF16)

if (!HaveSVE() && !HaveSME()) || !HaveBF16Ext() then UNDEFINED; integer n = UInt(Zn); integer m = UInt(Zm); integer da = UInt(Zda); integer index = UInt(i2);