fix: add quant_utils

Author: walker-ai

python/sglang/srt/layers/quantization/quant_utils.py

@@ -0,0 +1,166 @@
+# SPDX-License-Identifier: Apache-2.0
+# Adapted from https://github.com/vllm-project/vllm/blob/main/vllm/model_executor/layers/quantization/utils/quant_utils.py
+
+from typing import Optional
+
+import numpy
+import torch
+from sgl_kernel.scalar_type import ScalarType
+
+
+def get_pack_factor(num_bits):
+    assert 32 % num_bits == 0, f"Unsupported num_bits = {num_bits}"
+    return 32 // num_bits
+
+
+def pack_cols(
+    q_w: torch.Tensor,
+    num_bits: int,
+    size_k: int,
+    size_n: int,
+):
+    assert q_w.shape == (size_k, size_n)
+
+    pack_factor = get_pack_factor(num_bits)
+    assert size_n % pack_factor == 0
+
+    orig_device = q_w.device
+
+    q_w = q_w.cpu().numpy().astype(numpy.uint32)
+
+    q_res = numpy.zeros((size_k, size_n // pack_factor), dtype=numpy.uint32)
+
+    for i in range(pack_factor):
+        q_res |= q_w[:, i::pack_factor] << num_bits * i
+
+    q_res = torch.from_numpy(q_res.astype(numpy.int32)).to(orig_device)
+    q_res = q_res.contiguous()
+
+    return q_res
+
+
+def unpack_cols(
+    packed_q_w: torch.Tensor,
+    num_bits: int,
+    size_k: int,
+    size_n: int,
+):
+    pack_factor = get_pack_factor(num_bits)
+    assert size_n % pack_factor == 0
+    assert packed_q_w.shape == (
+        size_k,
+        size_n // pack_factor,
+    ), "packed_q_w.shape = {} size_k = {}, size_n = {} pack_Factor = {}".format(
+        packed_q_w.shape, size_k, size_n, pack_factor
+    )
+
+    orig_device = packed_q_w.device
+
+    packed_q_w_cpu = packed_q_w.cpu().numpy().astype(numpy.uint32)
+    q_res = numpy.zeros((size_k, size_n), dtype=numpy.uint32)
+
+    mask = (1 << num_bits) - 1
+    for i in range(pack_factor):
+        vals = packed_q_w_cpu & mask
+        packed_q_w_cpu >>= num_bits
+        q_res[:, i::pack_factor] = vals
+
+    q_res = torch.from_numpy(q_res.astype(numpy.int32)).to(orig_device)
+    q_res = q_res.contiguous()
+
+    return q_res
+
+
+def quantize_weights(
+    w: torch.Tensor,
+    quant_type: ScalarType,
+    group_size: Optional[int],
+    zero_points: bool = False,
+    ref_zero_points_after_scales: bool = False,
+):
+    assert (
+        quant_type.is_integer()
+    ), "Floating point quantization may work but has not been tested"
+    assert not zero_points or group_size is not None, (
+        "to have group zero points, group_size must be provided "
+        "(-1 group_size is channelwise)"
+    )
+
+    orig_device = w.device
+    orig_type = w.dtype
+    size_k, size_n = w.shape
+
+    assert w.is_floating_point(), "w must be float"
+
+    if group_size == -1:
+        group_size = size_k
+
+    # Reshape to [groupsize, -1]
+    if group_size is not None and group_size < size_k:
+        w = w.reshape((-1, group_size, size_n))
+        w = w.permute(1, 0, 2)
+        w = w.reshape((group_size, -1))
+
+    # Compute scale for each group
+    max_val = torch.max(w, 0, keepdim=True).values
+    min_val = torch.min(w, 0, keepdim=True).values
+
+    max_q_val = quant_type.max()
+    min_q_val = quant_type.min()
+
+    w_s = torch.Tensor([1.0]).to(w.device)  # unscaled case
+    maybe_w_zp = None
+    if group_size is not None:
+        if zero_points:
+            assert not quant_type.is_signed() and quant_type.max() > 0
+            w_s = (max_val - min_val).clamp(min=1e-5) / quant_type.max()
+            maybe_w_zp = (
+                torch.round(torch.abs(min_val / w_s)).clamp(min_q_val, max_q_val).int()
+            )
+        else:
+            # If the bias is such that there are no possible negative/positive
+            #  values, set the max value to inf to avoid divide by 0
+            w_s = torch.max(
+                abs(max_val / (max_q_val if max_q_val != 0 else torch.inf)),
+                abs(min_val / (min_q_val if min_q_val != 0 else torch.inf)),
+            )
+
+    # Quantize
+    w_q = torch.round(w / w_s).int() + (maybe_w_zp if zero_points else 0)
+    w_q = torch.clamp(w_q, min_q_val, max_q_val)
+
+    # Compute ref (dequantized)
+    # For some kernels (namely Machete) the zero-points are applied after the
+    # scales are applied, for this case computing the reference in similar way
+    # allows us to use tighter error tolerances in our unit tests.
+    if ref_zero_points_after_scales and maybe_w_zp is not None:
+        w_ref = w_q.to(orig_type) * w_s - maybe_w_zp.to(orig_type) * w_s
+    else:
+        w_ref = (w_q - (maybe_w_zp if zero_points else 0)).to(orig_type) * w_s
+
+    if quant_type.has_bias():
+        w_q += quant_type.bias
+
+    # Restore original shapes
+    if group_size is not None and group_size < size_k:
+
+        def reshape_w(w):
+            w = w.reshape((group_size, -1, size_n))
+            w = w.permute(1, 0, 2)
+            w = w.reshape((size_k, size_n)).contiguous()
+            return w
+
+        w_q = reshape_w(w_q)
+        w_ref = reshape_w(w_ref)
+        w_s = w_s.reshape((-1, size_n)).contiguous()
+
+    if maybe_w_zp is not None:
+        maybe_w_zp = maybe_w_zp.reshape((-1, size_n)).contiguous()
+        maybe_w_zp = maybe_w_zp.to(device=orig_device)
+
+    return (
+        w_ref.to(device=orig_device),
+        w_q.to(device=orig_device),
+        w_s if group_size is not None else None,
+        maybe_w_zp,
+    )