BFDOT (vector)

BFloat16 floating-point dot product (vector). This instruction delimits the source vectors into pairs of BFloat16 elements.

If FEAT_EBF16 is not implemented or FPCR.EBF is 0, this instruction:

• Performs an unfused sum-of-products of each pair of adjacent BFloat16 elements in the source vectors. The intermediate single-precision products are rounded before they are summed, and the intermediate sum is rounded before accumulation into the single-precision destination element that overlaps with the corresponding pair of BFloat16 elements in the source vectors.
• Uses the non-IEEE 754 Round-to-Odd rounding mode, which forces bit 0 of an inexact result to 1, and rounds an overflow to an appropriately signed Infinity.
• Flushes denormalized inputs and results to zero, as if FPCR.{FZ, FIZ} is {1, 1}.
• Disables alternative floating point behaviors, as if FPCR.AH is 0.

If FEAT_EBF16 is implemented and FPCR.EBF is 1, then this instruction:

• Performs a fused sum-of-products of each pair of adjacent BFloat16 elements in the source vectors. The intermediate single-precision products are not rounded before they are summed, but the intermediate sum is rounded before accumulation into the single-precision destination element that overlaps with the corresponding pair of BFloat16 elements in the source vectors.
• Follows all other floating-point behaviors that apply to single-precision arithmetic, as governed by FPCR.RMode, FPCR.FZ, FPCR.AH, and FPCR.FIZ.

Irrespective of FEAT_EBF16 and FPCR.EBF, this instruction:

• Does not modify the cumulative FPSR exception bits (IDC, IXC, UFC, OFC, DZC, and IOC).
• Disables trapped floating-point exceptions, as if the FPCR trap enable bits (IDE, IXE, UFE, OFE, DZE, and IOE) are all zero.
• Generates only the default NaN, as if FPCR.DN is 1.

ID_AA64ISAR1_EL1.BF16 indicates whether this instruction is supported.

Vector
(FEAT_BF16)

if !IsFeatureImplemented(FEAT_BF16) then UNDEFINED; integer n = UInt(Rn); integer m = UInt(Rm); integer d = UInt(Rd); constant integer datasize = 64 << UInt(Q); integer elements = datasize DIV 32;