v_div_fmas_f64 GPU Native ISA AMD Vector

V DIV FMAS F64 Vector Arithmetic

v_div_fmas_f64

Multiply two double-precision float inputs and add a third input using fused multiply add, then scale the exponent of the result by a fixed factor if…

Encoding

Verified bit-level encoding data is not yet available for this instruction. The instruction-format classification below (VOP3) is well-documented and stable; exact per-target opcode/field bit positions have not yet been imported from a verified source.
Format VOP3
Execution Unit

Operands

Operand details have not yet been curated for this instruction.

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

Input denormals are not flushed but output flushing is allowed. V_DIV_SCALE_F64, V_DIV_FMAS_F64 and V_DIV_FIXUP_F64 are all designed for use in a high precision division macro that utilizes V_RCP_F64 and V_MUL_F64 to compute the approximate result and then applies two steps of the Newton-Raphson method to converge to the quotient. If subnormal terms appear during this calculation then a loss of precision occurs. This loss of precision can be avoided by scaling the inputs and then post-scaling the quotient after Newton-Raphson is applied.

Related

More in Vector Arithmetic

Reference

AMDGPU / GFX ISA

Description

Multiply two double-precision float inputs and add a third input using fused multiply add, then scale the exponent of the result by a fixed factor if the vector condition code is set. Store the result into a vector register. This operation is designed for use in floating point division macros and relies on V_DIV_SCALE_F64 to set the vector condition code iff the quotient requires post-scaling.

Semantics

if VCC.u64[laneId] then D0.f64 = 2.0 ** 64 * fma(S0.f64, S1.f64, S2.f64) else D0.f64 = fma(S0.f64, S1.f64, S2.f64) endif

Example

v_div_fmas_f64 v[5:6], -1, -exec, |exec|

A real instruction accepted by the LLVM assembler, taken verbatim from LLVM's own AMDGPU MC test suite (gfx11). Not from an AMD document, and not authored here.

Sources