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Fix U32/U16/I8/I16 weight loading for quantized models #5

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Fix U32/U16/I8/I16 weight loading for quantized models #5

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e66f800
Fix U32/U16/I8/I16 weight loading for quantized models
duncanita Apr 19, 2026
40650bb
Use DTYPE_UNPACK for table-driven dtype dispatch
duncanita Apr 19, 2026
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37 changes: 14 additions & 23 deletions lib/mlx_lm/weight_utils.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -51,30 +51,21 @@ def _tensor_to_mlx(info, mx)
dtype_str = info["dtype"]
data = info["data"]

# For F32/float32, unpack as little-endian floats
if dtype_str == "F32" || dtype_str == "float32"
values = data.unpack("e*")
mx.array(values).reshape(shape)
elsif dtype_str == "F16"
# 16-bit float: unpack as uint16, create array as float32, then view as float16
values = data.unpack("S<*")
mx.array(values, dtype: mx.uint16).view(mx.float16).reshape(shape)
elsif dtype_str == "BF16"
values = data.unpack("S<*")
mx.array(values, dtype: mx.uint16).view(mx.bfloat16).reshape(shape)
elsif dtype_str == "I32" || dtype_str == "int32"
values = data.unpack("l<*")
mx.array(values, dtype: mx.int32).reshape(shape)
elsif dtype_str == "I64"
values = data.unpack("q<*")
mx.array(values, dtype: mx.int64).reshape(shape)
elsif dtype_str == "U8"
values = data.unpack("C*")
mx.array(values, dtype: mx.uint8).reshape(shape)
dtype_str = "F32" if dtype_str == "float32"
dtype_str = "I32" if dtype_str == "int32"

# F16/BF16 lack a direct unpack path; stage through uint16 + .view.
if dtype_str == "F16" || dtype_str == "BF16"
view_dtype = dtype_str == "F16" ? mx.float16 : mx.bfloat16
return mx.array(data.unpack("S<*"), dtype: mx.uint16).view(view_dtype).reshape(shape)
end

format_str, dtype_sym = DTYPE_UNPACK[dtype_str]
if format_str
mx.array(data.unpack(format_str), dtype: mx.__send__(dtype_sym)).reshape(shape)
else
# Fallback: try F32
values = data.unpack("e*")
mx.array(values).reshape(shape)
# Unknown dtype — interpret raw bytes as little-endian F32.
mx.array(data.unpack("e*")).reshape(shape)
end
end

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