v_cvt_pk_u8_f32 GPU Native ISA AMD Vector

Vector Arithmetic

v_cvt_pk_u8_f32

Convert a single-precision float value from the first input to an unsigned 8-bit integer value and pack the result into one byte of the third input…

Encoding

Binary Layout (AMD CDNA 5)
NEG
63:61
OMOD
60:59
SRC2
58:50
SRC1
49:41
SRC0
40:32
110101
31:26
1000100110
25:16
CLAMP
15
OPSEL
14:11
ABS
10:8
VDST
7:0
 

The ENC_VOP3 layout from AMD's machine-readable ISA specification (AMD CDNA 5). Opcode 550 in OP rebuilds 0x00000000D6260000, an identifier AMD lists for this encoding. Not the same in every generation: AMD CDNA 4 (opcode 477, field layout), AMD CDNA 3 (opcode 477, field layout), AMD CDNA 2 (opcode 477, field layout), AMD CDNA 1 (opcode 477, field layout), AMD RDNA 3.5 (field layout), AMD RDNA 3 (field layout), AMD RDNA 2 (opcode 350, field layout), AMD RDNA 1 (opcode 350, field layout). The same in AMD RDNA 4.

Format VOP3
Width 64 bits
Opcode 550
Identifier 0x00000000D6260000

Operands

  • VDST
    Written. Operand must be a vector GPR. Uses an 8-bit operand field. Data format: Unsigned 8-bit integral data. Packed 4-component value. (OPR_VGPR, FMT_NUM_PK4_U8)
  • 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)
  • SRC1
    Read. All operands. Covers all operands that are allowed as scalar or vector sources. Data format: Unsigned 32-bit integral data. (OPR_SRC, FMT_NUM_U32)
  • SRC2
    Read. All operands. Covers all operands that are allowed as scalar or vector sources. Data format: Unsigned 8-bit integral data. Packed 4-component value. (OPR_SRC, FMT_NUM_PK4_U8)

In AMD's order, as its machine-readable ISA specification lists them for the ENC_VOP3 encoding (AMD CDNA 5).

GFX Target Compatibility

TargetSupport
gfx1100✅ Supported

Related

More in Vector Arithmetic

Reference

AMDGPU / GFX ISA

Description

Convert a single-precision float value from the first input to an unsigned 8-bit integer value and pack the result into one byte of the third input using the second input as a byte select. Store the result into a vector register.

Semantics

tmp = (S2.u32 & 32'U(~(0xff << (S1.u32[1 : 0].u32 * 8U)))); tmp = (tmp | ((32'U(f32_to_u8(S0.f32)) & 255U) << (S1.u32[1 : 0].u32 * 8U))); D0.u32 = tmp

Example

v_cvt_pk_u8_f32 v5, v1, v2, s3

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