convert(gptoss): mxfp4 to ggml layout to avoid jit conversion (#12018)

* convert: return bytes written

* ggml flavor mxfp4

* simplify jit conversion

* comment

convert/convert_gptoss.go

@@ -172,7 +172,20 @@ func (m *mxfp4) WriteTo(w io.Writer) (int64, error) {
 		blocksDims[i] = int(d)
 	}
 
-	var blocks tensor.Tensor = tensor.New(tensor.WithShape(blocksDims...), tensor.WithBacking(b.Bytes()))
+	bts := b.Bytes()
+	var tmp [16]byte
+	for i := 0; i < b.Len(); i += 16 {
+		for j := range 8 {
+			// transform a1b2c3 ... x7y8z9 -> 71xa82yb93zc
+			a, b := bts[i+j], bts[i+j+8]
+			tmp[2*j+0] = (a & 0x0F) | (b << 4)
+			tmp[2*j+1] = (a >> 4) | (b & 0xF0)
+		}
+
+		copy(bts[i:i+16], tmp[:])
+	}
+
+	var blocks tensor.Tensor = tensor.New(tensor.WithShape(blocksDims...), tensor.WithBacking(bts))
 
 	var s bytes.Buffer
 	if _, err := m.scales.WriteTo(&s); err != nil {
@@ -206,5 +219,5 @@ func (m *mxfp4) WriteTo(w io.Writer) (int64, error) {
 		return 0, err
 	}
 
-	return 0, nil
+	return int64(len(u8s)), nil
 }

convert/reader.go

@@ -33,8 +33,8 @@ func (t tensorBase) Shape() []uint64 {
 const (
 	tensorKindFP32 uint32 = iota
 	tensorKindFP16
-	tensorKindMXFP4 = 4
 	tensorKindBF16  = 30
+	tensorKindMXFP4 = 39
 )
 
 func (t tensorBase) Kind() uint32 {

convert/reader_safetensors.go

@@ -188,17 +188,17 @@ func (st safetensor) WriteTo(w io.Writer) (int64, error) {
 
 	switch st.Kind() {
 	case tensorKindFP32:
-		return 0, binary.Write(w, binary.LittleEndian, f32s)
+		return int64(len(f32s) * 4), binary.Write(w, binary.LittleEndian, f32s)
 	case tensorKindFP16:
 		f16s := make([]uint16, len(f32s))
 		for i := range f32s {
 			f16s[i] = float16.Fromfloat32(f32s[i]).Bits()
 		}
 
-		return 0, binary.Write(w, binary.LittleEndian, f16s)
+		return int64(len(f16s) * 2), binary.Write(w, binary.LittleEndian, f16s)
 	case tensorKindBF16:
 		u8s := bfloat16.EncodeFloat32(f32s)
-		return 0, binary.Write(w, binary.LittleEndian, u8s)
+		return int64(len(u8s)), binary.Write(w, binary.LittleEndian, u8s)
 	default:
 		return 0, fmt.Errorf("unknown storage type: %d", st.Kind())
 	}

fs/ggml/ggml.go

@@ -290,24 +290,24 @@ func (t Tensor) blockSize() uint64 {
 func (t TensorType) BlockSize() uint64 {
 	switch t {
 	case
-		0,  // F32
-		1,  // F16
-		24, // I8
-		25, // I16
-		26, // I32
-		27, // I64
-		28, // F64
-		30: // BF16
+		TensorTypeF32,
+		TensorTypeF16,
+		TensorTypeI8,
+		TensorTypeI16,
+		TensorTypeI32,
+		TensorTypeI64,
+		TensorTypeF64,
+		TensorTypeBF16:
 		return 1
 	case
-		2,  // Q4_0
-		3,  // Q4_1
-		4,  // MXFP4
-		6,  // Q5_0
-		7,  // Q5_1
-		8,  // Q8_0
-		9,  // Q8_1
-		20: // IQ4_NL
+		TensorTypeQ4_0,
+		TensorTypeQ4_1,
+		TensorTypeQ5_0,
+		TensorTypeQ5_1,
+		TensorTypeQ8_0,
+		TensorTypeQ8_1,
+		tensorTypeIQ4_NL,
+		4, TensorTypeMXFP4:
 		return 32
 	default:
 		return 256
@@ -330,8 +330,6 @@ func (t TensorType) TypeSize() uint64 {
 		return 2 + blockSize/2
 	case TensorTypeQ4_1:
 		return 2 + 2 + blockSize/2
-	case TensorTypeMXFP4, 39:
-		return 1 + blockSize/2
 	case TensorTypeQ5_0:
 		return 2 + 4 + blockSize/2
 	case TensorTypeQ5_1:
@@ -382,6 +380,8 @@ func (t TensorType) TypeSize() uint64 {
 		return blockSize/8 + blockSize/16 + blockSize/32
 	case TensorTypeBF16:
 		return 2
+	case 4, TensorTypeMXFP4:
+		return 1 + blockSize/2
 	default:
 		return 0
 	}

fs/ggml/type.go

@@ -146,8 +146,6 @@ func (ftype FileType) ToTensorType() TensorType {
 		return TensorTypeQ4_0
 	case fileTypeQ4_1:
 		return TensorTypeQ4_1
-	case fileTypeMXFP4:
-		return TensorTypeMXFP4 // Formerly unused tensorTypeQ4_2
 	case FileTypeQ8_0:
 		return TensorTypeQ8_0
 	case fileTypeQ5_0:
@@ -176,6 +174,8 @@ func (ftype FileType) ToTensorType() TensorType {
 		return TensorTypeQ2_K
 	case FileTypeBF16:
 		return TensorTypeBF16
+	case fileTypeMXFP4:
+		return TensorTypeMXFP4
 	default:
 		slog.Warn("unsupported file type", "type", ftype)
 		return 0 // F32
@@ -191,7 +191,7 @@ const (
 	TensorTypeF16
 	TensorTypeQ4_0
 	TensorTypeQ4_1
-	TensorTypeMXFP4 // Formerly unused tensorTypeQ4_2
+	tensorTypeQ4_2
 	tensorTypeQ4_3 // unused by GGML
 	TensorTypeQ5_0
 	TensorTypeQ5_1
@@ -226,6 +226,7 @@ const (
 	tensorTypeIQ4_NL_4_4 // unused by GGML
 	tensorTypeIQ4_NL_4_8 // unused by GGML
 	tensorTypeIQ4_NL_8_8 // unused by GGML
+	TensorTypeMXFP4
 )
 
 // ParseFileType parses the provided GGUF file type
@@ -318,7 +319,7 @@ func (t TensorType) String() string {
 		return "F64"
 	case TensorTypeBF16:
 		return "BF16"
-	case TensorTypeMXFP4:
+	case 4, TensorTypeMXFP4:
 		return "MXFP4"
 	default:
 		return "unknown"

ml/backend/ggml/ggml.go

@@ -535,6 +535,7 @@ func (b *Backend) Load(ctx context.Context, progress func(float32)) error {
 				const BS = 17                             // MXFP4 block size
 				bts := make([]byte, 8*BS*format.KibiByte) // ~128k block aligned
 				var s uint64
+				var tmp [16]byte
 				for s < t.Size() {
 					// Stop if either the parent context has been canceled or if any of the other tensors returned an error
 					if err := ctx.Err(); err != nil {
@@ -546,37 +547,13 @@ func (b *Backend) Load(ctx context.Context, progress func(float32)) error {
 						return err
 					}
 					for j := range n / BS {
-						for i := 1; i < BS; i++ {
-							// swap nibbles
-							t_lo := bts[j*BS+i] & 0x0F
-							t_hi := bts[j*BS+i] & 0xF0
-							bts[j*BS+i] = (t_lo << 4) | (t_hi >> 4)
-						}
-						// transform aaaa...bbbb... to abababab...
-						oi := 0
-						tmp := [16]byte{}
 						for i := 1; i < 9; i++ {
-							blk_a0 := bts[j*BS+i] & 0xF0
-							blk_a1 := bts[j*BS+i] << 4
-							blk_b0 := bts[j*BS+i+8] >> 4
-							blk_b1 := bts[j*BS+i+8] & 0x0F
-							// swap once more
-							out0 := blk_a0 | blk_b0
-							out1 := blk_a1 | blk_b1
-							out_h0 := out0 & 0xF0
-							out_l0 := out0 & 0x0F
-							out_h1 := out1 & 0xF0
-							out_l1 := out1 & 0x0F
-							out0 = (out_h0 >> 4) | (out_l0 << 4)
-							out1 = (out_h1 >> 4) | (out_l1 << 4)
-							tmp[oi] = out0
-							oi++
-							tmp[oi] = out1
-							oi++
-						}
-						for i := range tmp {
-							bts[j*BS+i+1] = tmp[i]
+							// transform a1b2c3 ... x7y8z9 -> 71xa82yb93zc
+							a, b := bts[j*BS+i], bts[j*BS+i+8]
+							tmp[2*(i-1)] = (a & 0x0F) | (b << 4)
+							tmp[2*(i-1)+1] = (a >> 4) | (b & 0xF0)
 						}
+						copy(bts[j*BS+1:j*BS+17], tmp[:])
 					}
 
 					for _, tt := range tts {