aten/src/ATen/native/Scalar.cpp

#define TORCH_ASSERT_ONLY_METHOD_OPERATORS
#include <ATen/core/Tensor.h>
#include <ATen/Dispatch.h>

#ifndef AT_PER_OPERATOR_HEADERS
#include <ATen/Functions.h>
#include <ATen/NativeFunctions.h>
#else
#include <ATen/ops/_local_scalar_dense.h>
#include <ATen/ops/_local_scalar_dense_native.h>
#include <ATen/ops/item_native.h>
#endif

namespace at {
namespace native {

Scalar item(const Tensor& self) {
  auto numel = self.sym_numel();
  TORCH_CHECK(numel == 1, "a Tensor with ", numel, " elements cannot be converted to Scalar");
  if (self.is_sparse()) {
    if (self._nnz() == 0) return Scalar(0);
    if (self.is_coalesced()) return at::_local_scalar_dense(self._values());
    return at::_local_scalar_dense(self._values().sum());
  } else if (self.is_quantized()) {
    return self.dequantize().item();
  } else {
    return _local_scalar_dense(self);
  }
}

#if !defined(C10_MOBILE)
#define _AT_DISPATCH_SD_TYPES(TYPE, NAME, ...) \
  AT_DISPATCH_ALL_TYPES_AND_COMPLEX_AND8(      \
      kComplexHalf,                            \
      kHalf,                                   \
      kBool,                                   \
      kBFloat16,                               \
      kFloat8_e5m2,                            \
      kFloat8_e5m2fnuz,                        \
      kFloat8_e4m3fn,                          \
      kFloat8_e4m3fnuz,                        \
      TYPE,                                    \
      NAME,                                    \
      __VA_ARGS__)
#else
#define _AT_DISPATCH_SD_TYPES(TYPE, NAME, ...)     \
        AT_DISPATCH_ALL_TYPES_AND_COMPLEX_AND4(    \
            kComplexHalf, kHalf, kBool, kBFloat16, \
            TYPE, NAME, __VA_ARGS__)
#endif

Scalar _local_scalar_dense_cpu(const Tensor& self) {
  Scalar r;
  _AT_DISPATCH_SD_TYPES(self.scalar_type(), "_local_scalar_dense_cpu", [&] {
        scalar_t value = *self.data_ptr<scalar_t>();
        r = Scalar(value);
      });
  return r;
}

}} // at::native