BFMMLA (widening)

BFloat16 matrix multiply-accumulate to single-precision

This instruction multiplies the 2×4 matrix of BFloat16 values held in each 128-bit segment of the first source vector by the 4×2 matrix of BFloat16 values in the corresponding segment of the second source vector.

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

• Calculates the intermediate single-precision results as a sum of two unfused sum-of-products using two pairs of adjacent BFloat16 values from each of the source vectors, and rounds the results before accumulation into the 2×2 matrix of single-precision results in the corresponding segment of the destination vector. This is equivalent to accumulating a 4-way dot product per destination element.
• 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}.
• Honors FPCR.AH when generating a default NaN result, otherwise disables alternative floating point behaviors, as if FPCR.AH is 0.

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

• Calculates the intermediate single-precision results as a sum of two fused sum-of-products using two pairs of adjacent BFloat16 values from each of the source vectors, and rounds the results before accumulation into the 2×2 matrix of single-precision results in the destination vector. This is equivalent to accumulating a 4-way dot product per destination element.
• 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.

This instruction is unpredicated and vector length agnostic.

ID_AA64ZFR0_EL1.BF16 indicates whether this instruction is implemented.

This instruction is illegal when executed in Streaming SVE mode, unless FEAT_SME_FA64 is implemented and enabled.

SVE
(FEAT_SVE && FEAT_BF16)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) || !IsFeatureImplemented(FEAT_BF16) then EndOfDecode(Decode_UNDEF); end; let n : integer = UInt(Zn); let m : integer = UInt(Zm); let da : integer = UInt(Zda);