Hi, Max:
On 1/8/2026 11:16 PM, Max Chou wrote:
> This patchset adds support for the OCP (Open Compute Project) 8-bit and
> 4-bit floating-point formats, along with the RISC-V Zvfofp8min and
> Zvfofp4min vector extensions that provide conversion operations for
> these formats.
>
> OCP Floating-Point Formats
> * The OCP FP8 specification defines two 8-bit floating-point formats:
> - E4M3: 4-bit exponent, 3-bit mantissa
> * No infinity representation; only 0x7f and 0xff are NaN
> - E5M2: 5-bit exponent, 2-bit mantissa
> * IEEE-like format with infinity representation
> * Multiple NaN encodings supported
> * The OCP FP4 specification defines the E2M1 format:
> - E2M1: 2-bit exponent, 1-bit mantissa
> * No NaN representation
>
> RISC-V ISA Extensions
> * Zvfofp8min (Version 0.2.1):
> The Zvfofp8min extension provides minimal vector conversion support
> for OFP8 formats. It requires the Zve32f extension and leverages the
> altfmt field in the VTYPE CSR (introduced by Zvfbfa) to select between
> E4M3 (altfmt=0) and E5M2 (altfmt=1) formats.
> - Canonical NaN for both E4M3 and E5M2 is 0x7f
> - All NaNs are treated as quiet NaNs
> Instructions added/extended:
> - vfwcvtbf16.f.f.v: OFP8 to BF16 widening conversion
> - vfncvtbf16.f.f.w: BF16 to OFP8 narrowing conversion
> - vfncvtbf16.sat.f.f.w: BF16 to OFP8 with saturation (new)
> - vfncvt.f.f.q: FP32 to OFP8 quad-narrowing conversion (new)
> - vfncvt.sat.f.f.q: FP32 to OFP8 with saturation (new)
>
> * Zvfofp4min (Version 0.1):
> The Zvfofp4min extension provides minimal vector conversion support
> for the OFP4 E2M1 format. It requires the Zve32f extension.
> Instructions added:
> - vfext.vf2: OFP4 E2M1 to OFP8 E4M3 widening conversion
>
> Modifications
> * Softfloat library:
> - New float8_e4m3 and float8_e5m2 types with NaN checking functions
> - New float4_e2m1 type for OFP4 support
> - Conversion functions: bfloat16/float32 <-> float8_e4m3/float8_e5m2
> - Conversion function: float4_e2m1 -> float8_e4m3
> - Implementation-defined behavior flags in float_status:
> * ocp_fp8e5m2_no_signal_nan: Treat all E5M2 NaNs as quiet
> * ocp_fp8_same_canonical_nan: Use 0x7f as canonical NaN for all OFP8
> * RISC-V target:
> - CPU configuration properties for Zvfofp8min and Zvfofp4min
> - Extension implied rules (Zvfofp8min requires Zve32f and Zvfbfa)
> - Vector helper functions for OFP8/OFP4 conversion instructions
> - Disassembler support for new instructions
>
Nice work! The code quality looks good. I've been working on similar stuff
recently, so happy to review.
A quick suggestion: run checkpatch.pl to catch any style issues.
Also, are we planning to add softfloat unit tests for OCP floating-point
formats? Would be great for code quality coverage.
Thanks,
Chao
> References
> * OCP FP8 specification:
> https://www.opencompute.org/documents/ocp-8-bit-floating-point-specification-ofp8-revision-1-0-2023-12-01-pdf-1
> * Zvfofp8min specification (v0.2.1 commit e1e20a7):
> https://github.com/aswaterman/riscv-misc/blob/main/isa/zvfofp8min.adoc
> * Zvfofp4min specification (v0.1 commit e1e20a7):
> https://github.com/aswaterman/riscv-misc/blob/main/isa/zvfofp4min.adoc
>
> PS: This series depends on the Zvfbfa extension patchset which introduces:
> - The altfmt field in VTYPE CSR
> - BF16 vector operations infrastructure
> - vfwcvtbf16.f.f.v and vfncvtbf16.f.f.w base instructions
>
> Based-on: 20260108132631.9429-1-max.chou@sifive.com
>
> Max Chou (18):
> target/riscv: rvv: Fix NOP_UU_B vs2 width
> fpu/softfloat: Add OCP(Open Compute Project) OFP8 data type
> fpu/softfloat: Add convert operations(bf16, fp32) for OFP8 data types
> fpu/softfloat: Add OCP(Open Compute Project) OFP4 data type
> fpu/softfloat: Add OCP FP4 E2M1 to OCP FP8 E4M3 convert operation
> target/riscv: Add cfg properity for Zvfofp8min extension
> target/riscv: Add implied rules for Zvfofp8min extension
> target/riscv: rvv: Make vfwcvtbf16.f.f.v support OFP8 to BF16
> conversion for Zvfofp8min extension
> target/riscv: rvv: Make vfncvtbf16.f.f.w support BF16 to OFP8
> conversion for Zvfofp8min extension
> target/riscv: rvv: Add vfncvtbf16.sat.f.f.w instruction for Zvfofp8min
> extension
> target/riscv: rvv: Add vfncvt.f.f.q and vfncvt.sat.f.f.q instructions
> for Zvfofp8min extension
> target/riscv: Expose Zvfofp8min properity
> disas/riscv: Add support of Zvfofp8min extension
> target/riscv: Add cfg properity for Zvfofp4min extension
> target/riscv: Add implied rules for Zvfofp4min extension
> target/riscv: rvv: Add vfext.vf2 instruction for Zvfofp4min extension
> target/riscv: Expose Zvfofp4min properity
> disas/riscv: Add support of Zvfofp4min extension
>
> disas/riscv.c | 12 +
> fpu/softfloat-parts.c.inc | 77 +++++-
> fpu/softfloat-specialize.c.inc | 57 ++++-
> fpu/softfloat.c | 274 +++++++++++++++++++++
> include/fpu/softfloat-helpers.h | 20 ++
> include/fpu/softfloat-types.h | 28 +++
> include/fpu/softfloat.h | 124 ++++++++++
> target/riscv/cpu.c | 35 ++-
> target/riscv/cpu_cfg_fields.h.inc | 2 +
> target/riscv/helper.h | 15 ++
> target/riscv/insn32.decode | 8 +
> target/riscv/insn_trans/trans_rvbf16.c.inc | 32 ++-
> target/riscv/insn_trans/trans_rvofp4.c.inc | 54 ++++
> target/riscv/insn_trans/trans_rvofp8.c.inc | 115 +++++++++
> target/riscv/insn_trans/trans_rvv.c.inc | 39 +++
> target/riscv/tcg/tcg-cpu.c | 15 ++
> target/riscv/translate.c | 2 +
> target/riscv/vector_helper.c | 131 +++++++++-
> 18 files changed, 1022 insertions(+), 18 deletions(-)
> create mode 100644 target/riscv/insn_trans/trans_rvofp4.c.inc
> create mode 100644 target/riscv/insn_trans/trans_rvofp8.c.inc
>