ggml : add NVFP4 quantization type support (#19769)

* WIP: add NVFP4 quantization support

* tests

* improve NVFP4 dot product implementation performance and fix bad super call

* typo

* Use nvfp4 kvalues

* vulkan : fix NVFP4 shader compilation by including kvalues_mxfp4 lookup table

* vulcal and perf fixes

* wip

* Fix metal

* fix vulcan

* Rename threshold & fix wrong scale

* Fix MOE

* Shelf backend implementations (CUDA, Metal, Vulkan, arch-specific SIMD)

Remove NVFP4 support from GPU backends and architecture-specific
optimized dot products. These should be added in separate PRs so
backend specialists can review them independently.

Reverted files:
- ggml-cuda: common.cuh, convert.cu, mmq.cu/cuh, mmvq.cu, vecdotq.cuh,
  quantize.cu/cuh, mma.cuh, ggml-cuda.cu, fattn-tile.cuh
- ggml-metal: ggml-metal.metal, ggml-metal-device.cpp, ggml-metal-impl.h,
  ggml-metal-ops.cpp
- ggml-vulkan: ggml-vulkan.cpp, all vulkan-shaders/*
- ggml-cpu arch: arm/quants.c, x86/quants.c, powerpc/quants.c, s390/quants.c

Core NVFP4 support (type definition, CPU fallback dot product,
quantization, dequantization, conversion) is retained.

* Fix arch-fallback.h: add NVFP4 generic fallback for all platforms

After shelving backend-specific SIMD implementations, the generic
CPU dot product needs to be aliased on ARM, x86, PowerPC, and s390
platforms that previously relied on arch-specific versions.

* quantize: add NVFP4 as a quantization type option

* Fix ggml_fp32_to_ue4m3: handle subnormal values

Previously, values with ue4m3_exp <= 0 were clamped to 0, causing
all small scales to underflow. This made NVFP4 quantization via
llama-quantize produce garbage (PPL = 5.8M) since typical transformer
weights have amax/6.0 in the range 0.001-0.01, which falls in the
UE4M3 subnormal range.

Now subnormals are properly encoded as man * 2^-9 (exp=0, man=1..7),
matching the decode path in ggml_ue4m3_to_fp32.

Result: NVFP4 requantization now produces PPL = 15.25 (vs F16 = 14.33),
comparable to Q4_1 (PPL = 15.81) at slightly lower BPW (4.70 vs 5.15).

* Restore ARM NEON NVFP4 dot product implementation

Restores the optimized ggml_vec_dot_nvfp4_q8_0 for ARM NEON using
vqtbl1q_s8 lookup and ggml_vdotq_s32 dot products.

tg128 performance: 4.37 t/s (generic) -> 13.66 t/s (NEON) = 3.1x speedup

* Optimize ARM NEON NVFP4 dot product: LUT + vpaddq + vfmaq

- Add ue4m3_scale_lut[128] to ggml-common.h replacing branch-heavy
  ggml_ue4m3_to_fp32() in the hot loop
- Use vpaddq_s32 for pairwise int32 reduction instead of vaddvq_s32
- Accumulate with vfmaq_f32 into float32x4_t vector accumulators

tg128: 8.1 -> 31.0 t/s (3.8x speedup, 77% of Q4_1 speed)

* ARM NEON NVFP4: rearrange q8 to match nibble layout

Alternative approach: rearrange q8 data to match the NVFP4 lo/hi
nibble layout instead of rearranging the looked-up NVFP4 values.
Eliminates vcombine_s8(vget_low, vget_low) shuffles.

Performance is equivalent (~18.5 t/s) - the bottleneck is the 2x
block overhead from QK=16 vs QK=32, not the shuffle instructions.

* CPU only backend 64 super-block layout

* cleanup

* Remove unused LUT

* int

* exclude NVFP4 from unsupported ops in metal build

* remove quantization for now

* store scales as native UE4M3, preserve original model bits when possible

* Update convert_hf_to_gguf.py

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* correct comment

* format

* reduce duplication and cleanup

* Address comments

* move detection to prepare_tensors

* Use math instead of const

* Move

* fix comment

* Shelf quantize tests

* Rebase and move check

* cleanup

* lint

* Update gguf-py/gguf/scripts/gguf_convert_endian.py

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* Use fallback quant config

* Simplify

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* organize

* Refactor

* Update convert_hf_to_gguf.py

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* Update convert_hf_to_gguf.py

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* Update convert_hf_to_gguf.py

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

* add quantize_nvfp4 (required for test_quants.py)

* add quantize_nvfp4 (required for test_quants.py)

* add quantize_nvfp4 (required for test_quants.py)

* fix return type

---------

Co-authored-by: Sigbjørn Skjæret <sigbjorn.skjaeret@scala.com>

ggml/src/ggml-quants.c

@@ -304,6 +304,41 @@ void quantize_row_mxfp4_ref(const float * GGML_RESTRICT x, block_mxfp4 * GGML_RE
     }
 }
 
+void quantize_row_nvfp4_ref(const float * GGML_RESTRICT x, block_nvfp4 * GGML_RESTRICT y, int64_t k) {
+    static const int qk = QK_NVFP4;
+    static const int qk_sub = QK_NVFP4_SUB;
+    static const int n_sub = QK_NVFP4 / QK_NVFP4_SUB;
+
+    assert(k % qk == 0);
+
+    const int nb = k / qk;
+
+    for (int i = 0; i < nb; i++) {
+        for (int s = 0; s < n_sub; s++) {
+            const float * xb = x + i*qk + s*qk_sub;
+
+            float amax = 0.0f;
+            for (int j = 0; j < qk_sub; j++) {
+                if (amax < fabsf(xb[j])) {
+                    amax = fabsf(xb[j]);
+                }
+            }
+
+            // UE4M3 scale: amax / 6.0 maps the max E2M1 value (6.0) to amax
+            const uint8_t ue = ggml_fp32_to_ue4m3(amax / 6.0f);
+            y[i].d[s] = ue;
+            const float d = ggml_ue4m3_to_fp32(ue);
+
+            for (int j = 0; j < qk_sub/2; ++j) {
+                const uint8_t x0 = best_index_mxfp4(xb[0        + j], d);
+                const uint8_t x1 = best_index_mxfp4(xb[qk_sub/2 + j], d);
+
+                y[i].qs[s*(qk_sub/2) + j] = x0 | (x1 << 4);
+            }
+        }
+    }
+}
+
 void dequantize_row_q4_0(const block_q4_0 * GGML_RESTRICT x, float * GGML_RESTRICT y, int64_t k) {
     static const int qk = QK4_0;
 
@@ -434,6 +469,31 @@ void dequantize_row_mxfp4(const block_mxfp4 * GGML_RESTRICT x, float * GGML_REST
     }
 }
 
+void dequantize_row_nvfp4(const block_nvfp4 * GGML_RESTRICT x, float * GGML_RESTRICT y, int64_t k) {
+    static const int qk = QK_NVFP4;
+    static const int qk_sub = QK_NVFP4_SUB;
+    static const int n_sub = QK_NVFP4 / QK_NVFP4_SUB;
+
+    assert(k % qk == 0);
+
+    const int nb = k / qk;
+
+    for (int i = 0; i < nb; i++) {
+        for (int s = 0; s < n_sub; s++) {
+            const float d = ggml_ue4m3_to_fp32(x[i].d[s]);
+            float * yb = y + i*qk + s*qk_sub;
+
+            for (int j = 0; j < qk_sub/2; ++j) {
+                const int8_t v0 = kvalues_mxfp4[x[i].qs[s*(qk_sub/2) + j] & 0x0F];
+                const int8_t v1 = kvalues_mxfp4[x[i].qs[s*(qk_sub/2) + j] >>   4];
+
+                yb[j + 0       ] = v0*d;
+                yb[j + qk_sub/2] = v1*d;
+            }
+        }
+    }
+}
+
 //
 // 2-6 bit quantization in super-blocks
 //
@@ -2098,6 +2158,12 @@ size_t quantize_mxfp4(const float * GGML_RESTRICT src, void * GGML_RESTRICT dst,
     return nrow * ggml_row_size(GGML_TYPE_MXFP4, n_per_row);
 }
 
+size_t quantize_nvfp4(const float * GGML_RESTRICT src, void * GGML_RESTRICT dst, int64_t nrow, int64_t n_per_row, const float * quant_weights) {
+    GGML_UNUSED(quant_weights);
+    quantize_row_nvfp4_ref(src, dst, (int64_t)nrow*n_per_row);
+    return nrow * ggml_row_size(GGML_TYPE_NVFP4, n_per_row);
+}
+
 // ====================== Ternary (de)-quantization (BitNet b1.58 and TriLMs)
 
 void quantize_row_tq1_0_ref(const float * GGML_RESTRICT x, block_tq1_0 * GGML_RESTRICT y, int64_t k) {
@@ -5244,6 +5310,12 @@ bool ggml_validate_row_data(enum ggml_type type, const void * data, size_t nbyte
             {
                 VALIDATE_ROW_DATA_E_E8M0_IMPL(block_mxfp4, data, nb);
             } break;
+        case GGML_TYPE_NVFP4:
+            {
+                // UE4M3 scales are uint8_t — all byte values are valid
+                GGML_UNUSED(data);
+                GGML_UNUSED(nb);
+            } break;
         case GGML_TYPE_Q2_K:
             {
                 VALIDATE_ROW_DATA_DM_F16_IMPL(block_q2_K, data, nb, d, dmin);