v_cvt_f16_f32 GPU Native ISA AMD Vector

Vector Arithmetic

v_cvt_f16_f32

Convert from a single-precision float input to a half-precision float value and store the result into a vector register.

Encoding

Binary Layout (AMD CDNA 5)
0111111
31:25
VDST
24:17
unassigned
16
0001010
15:9
SRC0
8:0
 

The ENC_VOP1 layout from AMD's machine-readable ISA specification (AMD CDNA 5). Opcode 10 in OP rebuilds 0x7E001400, an identifier AMD lists for this encoding. Bits marked unassigned have no field in the specification. Not the same in every generation: AMD CDNA 4 (field layout), AMD CDNA 3 (field layout), AMD CDNA 2 (field layout), AMD CDNA 1 (field layout), AMD RDNA 3.5 (field layout), AMD RDNA 3 (field layout), AMD RDNA 2 (field layout), AMD RDNA 1 (field layout). The same in AMD RDNA 4.

Format VOP1
Width 32 bits
Opcode 10
Identifier 0x7E001400

Operands

  • VDST
    Written. Operand must be a vector GPR. Uses an 8-bit operand field. Data format: 16-bit half-precision floating point value. (OPR_VGPR, FMT_NUM_F16)
  • SRC0
    Read. All operands. Covers all operands that are allowed as scalar or vector sources. Data format: 32-bit single-precision floating point value. (OPR_SRC, FMT_NUM_F32)

In AMD's order, as its machine-readable ISA specification lists them for the ENC_VOP1 encoding (AMD CDNA 5).

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

0.5ULP accuracy, supports input modifiers and creates FP16 denormals when appropriate. Flush denorms on output if specified based on DP denorm mode. Output rounding based on DP rounding mode.

Related

More in Vector Arithmetic

Reference

AMDGPU / GFX ISA

Semantics

D0.f16 = f32_to_f16(S0.f32)

Example

v_cvt_f16_f32 v5.l, v1

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

Sources