Make more constexpr available on device for cuIO

cpp/include/cudf/detail/utilities/integer_utils.hpp

@@ -73,7 +73,7 @@ CUDF_HOST_DEVICE constexpr S round_up_safe(S number_to_round, S modulus)
  * `modulus` is positive and does not check for overflow.
  */
 template <typename S>
-constexpr S round_down_safe(S number_to_round, S modulus) noexcept
+CUDF_HOST_DEVICE constexpr S round_down_safe(S number_to_round, S modulus) noexcept
 {
   auto remainder    = number_to_round % modulus;
   auto rounded_down = number_to_round - remainder;
@@ -113,24 +113,26 @@ CUDF_HOST_DEVICE constexpr S round_up_unsafe(S number_to_round, S modulus) noexc
  * the result will be incorrect
  */
 template <typename S, typename T>
-constexpr S div_rounding_up_unsafe(S const& dividend, T const& divisor) noexcept
+CUDF_HOST_DEVICE constexpr S div_rounding_up_unsafe(S const& dividend, T const& divisor) noexcept
 {
   return (dividend + divisor - 1) / divisor;
 }
 
 namespace detail {
 template <typename I>
-constexpr I div_rounding_up_safe(std::integral_constant<bool, false>,
-                                 I dividend,
-                                 I divisor) noexcept
+CUDF_HOST_DEVICE constexpr I div_rounding_up_safe(cuda::std::integral_constant<bool, false>,
+                                                  I dividend,
+                                                  I divisor) noexcept
 {
   // TODO: This could probably be implemented faster
   return (dividend > divisor) ? 1 + div_rounding_up_unsafe(dividend - divisor, divisor)
                               : (dividend > 0);
 }
 
 template <typename I>
-constexpr I div_rounding_up_safe(std::integral_constant<bool, true>, I dividend, I divisor) noexcept
+CUDF_HOST_DEVICE constexpr I div_rounding_up_safe(cuda::std::integral_constant<bool, true>,
+                                                  I dividend,
+                                                  I divisor) noexcept
 {
   auto quotient  = dividend / divisor;
   auto remainder = dividend % divisor;
@@ -156,9 +158,9 @@ constexpr I div_rounding_up_safe(std::integral_constant<bool, true>, I dividend,
  * the non-integral division `dividend/divisor`
  */
 template <typename I>
-constexpr I div_rounding_up_safe(I dividend, I divisor) noexcept
+CUDF_HOST_DEVICE constexpr I div_rounding_up_safe(I dividend, I divisor) noexcept
 {
-  using i_is_a_signed_type = std::integral_constant<bool, std::is_signed_v<I>>;
+  using i_is_a_signed_type = cuda::std::integral_constant<bool, cuda::std::is_signed_v<I>>;
   return detail::div_rounding_up_safe(i_is_a_signed_type{}, dividend, divisor);
 }
 

cpp/include/cudf/fixed_point/temporary.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, NVIDIA CORPORATION.
+ * Copyright (c) 2021-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -54,7 +54,7 @@ auto to_string(T value) -> std::string
 }
 
 template <typename T>
-constexpr auto abs(T value)
+CUDF_HOST_DEVICE constexpr auto abs(T value)
 {
   return value >= 0 ? value : -value;
 }
@@ -72,7 +72,7 @@ CUDF_HOST_DEVICE inline auto max(T lhs, T rhs)
 }
 
 template <typename BaseType>
-constexpr auto exp10(int32_t exponent)
+CUDF_HOST_DEVICE constexpr auto exp10(int32_t exponent)
 {
   BaseType value = 1;
   while (exponent > 0)

cpp/include/cudf/io/text/detail/multistate.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, NVIDIA CORPORATION.
+ * Copyright (c) 2021-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,6 +18,8 @@
 
 #include <cudf/utilities/export.hpp>
 
+#include <cuda/functional>
+
 #include <cstdint>
 
 namespace CUDF_EXPORT cudf {
@@ -45,7 +47,7 @@ struct multistate {
    *
    * @note: The behavior of this function is undefined if size() => max_segment_count
    */
-  constexpr void enqueue(uint8_t head, uint8_t tail)
+  CUDF_HOST_DEVICE constexpr void enqueue(uint8_t head, uint8_t tail)
   {
     _heads |= (head & 0xFu) << (_size * 4);
     _tails |= (tail & 0xFu) << (_size * 4);
@@ -55,17 +57,17 @@ struct multistate {
   /**
    * @brief get's the number of segments this multistate represents
    */
-  [[nodiscard]] constexpr uint8_t size() const { return _size; }
+  [[nodiscard]] CUDF_HOST_DEVICE constexpr uint8_t size() const { return _size; }
 
   /**
    * @brief get's the highest (____, tail] value this multistate represents
    */
-  [[nodiscard]] constexpr uint8_t max_tail() const
+  [[nodiscard]] CUDF_HOST_DEVICE constexpr uint8_t max_tail() const
   {
     uint8_t maximum = 0;
 
     for (uint8_t i = 0; i < _size; i++) {
-      maximum = std::max(maximum, get_tail(i));
+      maximum = cuda::std::max(maximum, get_tail(i));
     }
 
     return maximum;
@@ -74,15 +76,15 @@ struct multistate {
   /**
    * @brief get's the Nth (head, ____] value state this multistate represents
    */
-  [[nodiscard]] constexpr uint8_t get_head(uint8_t idx) const
+  [[nodiscard]] CUDF_HOST_DEVICE constexpr uint8_t get_head(uint8_t idx) const
   {
     return (_heads >> (idx * 4)) & 0xFu;
   }
 
   /**
    * @brief get's the Nth (____, tail] value state this multistate represents
    */
-  [[nodiscard]] constexpr uint8_t get_tail(uint8_t idx) const
+  [[nodiscard]] CUDF_HOST_DEVICE constexpr uint8_t get_tail(uint8_t idx) const
   {
     return (_tails >> (idx * 4)) & 0xFu;
   }

cpp/include/cudf/strings/detail/convert/fixed_point.cuh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2024, NVIDIA CORPORATION.
+ * Copyright (c) 2021-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,7 @@
 
 #include <cudf/fixed_point/temporary.hpp>
 
+#include <cuda/std/limits>
 #include <cuda/std/optional>
 #include <cuda/std/type_traits>
 #include <thrust/pair.h>
@@ -46,7 +47,7 @@ __device__ inline thrust::pair<UnsignedDecimalType, int32_t> parse_integer(
   // highest value where another decimal digit cannot be appended without an overflow;
   // this preserves the most digits when scaling the final result for this type
   constexpr UnsignedDecimalType decimal_max =
-    (std::numeric_limits<UnsignedDecimalType>::max() - 9L) / 10L;
+    (cuda::std::numeric_limits<UnsignedDecimalType>::max() - 9L) / 10L;
 
   __uint128_t value  = 0;  // for checking overflow
   int32_t exp_offset = 0;
@@ -90,7 +91,8 @@ __device__ inline thrust::pair<UnsignedDecimalType, int32_t> parse_integer(
 template <bool check_only = false>
 __device__ cuda::std::optional<int32_t> parse_exponent(char const* iter, char const* iter_end)
 {
-  constexpr uint32_t exponent_max = static_cast<uint32_t>(std::numeric_limits<int32_t>::max());
+  constexpr uint32_t exponent_max =
+    static_cast<uint32_t>(cuda::std::numeric_limits<int32_t>::max());
 
   // get optional exponent sign
   int32_t const exp_sign = [&iter] {

cpp/include/cudf/strings/detail/convert/fixed_point_to_string.cuh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, NVIDIA CORPORATION.
+ * Copyright (c) 2023-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,6 +17,8 @@
 
 #include <cudf/strings/detail/convert/int_to_string.cuh>
 
+#include <cuda/std/functional>
+
 namespace cudf::strings::detail {
 
 /**
@@ -33,7 +35,7 @@ __device__ inline int32_t fixed_point_string_size(__int128_t const& value, int32
   auto const abs_value = numeric::detail::abs(value);
   auto const exp_ten   = numeric::detail::exp10<__int128_t>(-scale);
   auto const fraction  = count_digits(abs_value % exp_ten);
-  auto const num_zeros = std::max(0, (-scale - fraction));
+  auto const num_zeros = cuda::std::max(0, (-scale - fraction));
   return static_cast<int32_t>(value < 0) +    // sign if negative
          count_digits(abs_value / exp_ten) +  // integer
          1 +                                  // decimal point
@@ -66,7 +68,7 @@ __device__ inline void fixed_point_to_string(__int128_t const& value, int32_t sc
   if (value < 0) *out_ptr++ = '-';  // add sign
   auto const abs_value = numeric::detail::abs(value);
   auto const exp_ten   = numeric::detail::exp10<__int128_t>(-scale);
-  auto const num_zeros = std::max(0, (-scale - count_digits(abs_value % exp_ten)));
+  auto const num_zeros = cuda::std::max(0, (-scale - count_digits(abs_value % exp_ten)));
 
   out_ptr += integer_to_string(abs_value / exp_ten, out_ptr);  // add the integer part
   *out_ptr++ = '.';                                            // add decimal point

cpp/include/cudf/strings/detail/convert/int_to_string.cuh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021-2022, NVIDIA CORPORATION.
+ * Copyright (c) 2021-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -67,7 +67,7 @@ __device__ inline size_type integer_to_string(IntegerType value, char* d_buffer)
  * @return size_type number of digits in input value
  */
 template <typename IntegerType>
-constexpr size_type count_digits(IntegerType value)
+__device__ constexpr size_type count_digits(IntegerType value)
 {
   if (value == 0) return 1;
   bool const is_negative = cuda::std::is_signed<IntegerType>() ? (value < 0) : false;

cpp/include/cudf/strings/detail/strings_children.cuh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2024, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -41,6 +41,21 @@ namespace cudf {
 namespace strings {
 namespace detail {
 
+template <typename Iter>
+struct string_offsets_fn {
+  Iter _begin;
+  size_type _strings_count;
+  constexpr string_offsets_fn(Iter begin, size_type strings_count)
+    : _begin{begin}, _strings_count{strings_count}
+  {
+  }
+
+  __device__ constexpr size_type operator()(size_type idx) const noexcept
+  {
+    return idx < _strings_count ? static_cast<size_type>(_begin[idx]) : size_type{0};
+  };
+};
+
 /**
  * @brief Gather characters to create a strings column using the given string-index pair iterator
  *
@@ -133,11 +148,8 @@ std::pair<std::unique_ptr<column>, int64_t> make_offsets_child_column(
   // using exclusive-scan technically requires strings_count+1 input values even though
   // the final input value is never used.
   // The input iterator is wrapped here to allow the 'last value' to be safely read.
-  auto map_fn = cuda::proclaim_return_type<size_type>(
-    [begin, strings_count] __device__(size_type idx) -> size_type {
-      return idx < strings_count ? static_cast<size_type>(begin[idx]) : size_type{0};
-    });
-  auto input_itr = cudf::detail::make_counting_transform_iterator(0, map_fn);
+  auto input_itr =
+    cudf::detail::make_counting_transform_iterator(0, string_offsets_fn{begin, strings_count});
   // Use the sizes-to-offsets iterator to compute the total number of elements
   auto const total_bytes =
     cudf::detail::sizes_to_offsets(input_itr, input_itr + strings_count + 1, d_offsets, stream);

cpp/src/io/csv/datetime.cuh

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2024, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -197,7 +197,7 @@ __inline__ __device__ cuda::std::chrono::hh_mm_ss<duration_ms> extract_time_of_d
 /**
  * @brief Checks whether `c` is decimal digit
  */
-constexpr bool is_digit(char c) { return c >= '0' and c <= '9'; }
+__device__ constexpr bool is_digit(char c) { return c >= '0' and c <= '9'; }
 
 /**
  * @brief Parses a datetime string and computes the corresponding timestamp.

cpp/src/io/json/write_json.cu

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023-2024, NVIDIA CORPORATION.
+ * Copyright (c) 2023-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -376,6 +376,48 @@ std::unique_ptr<column> struct_to_strings(table_view const& strings_columns,
     {});
 }
 
+struct scatter_fn {
+  column_device_view _col;
+  size_type* _d_strview_offsets;
+  string_view* _d_strviews;
+  size_type* _labels;
+  size_type* _list_offsets;
+  column_device_view _d_strings_children;
+  string_view _element_seperator;
+  string_view _element_narep;
+
+  scatter_fn(column_device_view col,
+             size_type* d_strview_offsets,
+             string_view* d_strviews,
+             size_type* labels,
+             size_type* list_offsets,
+             column_device_view d_strings_children,
+             string_view element_separator,
+             string_view element_narep) noexcept
+    : _col{col},
+      _d_strview_offsets{d_strview_offsets},
+      _d_strviews{d_strviews},
+      _labels{labels},
+      _list_offsets{list_offsets},
+      _d_strings_children{d_strings_children},
+      _element_seperator{element_separator},
+      _element_narep{element_narep}
+  {
+  }
+
+  __device__ void operator()(size_type idx) const
+  {
+    auto const label         = _labels[idx];
+    auto const sublist_index = idx - _list_offsets[label];
+    auto const strview_index = _d_strview_offsets[label] + sublist_index * 2 + 1;
+    // value or na_rep
+    auto const strview         = _d_strings_children.element<cudf::string_view>(idx);
+    _d_strviews[strview_index] = _d_strings_children.is_null(idx) ? _element_narep : strview;
+    // separator
+    if (sublist_index != 0) { _d_strviews[strview_index - 1] = _element_seperator; }
+  }
+};
+
 /**
  * @brief Concatenates a list of strings columns into a single strings column.
  *
@@ -461,24 +503,14 @@ std::unique_ptr<column> join_list_of_strings(lists_column_view const& lists_stri
   thrust::for_each(rmm::exec_policy_nosync(stream),
                    thrust::make_counting_iterator<size_type>(0),
                    thrust::make_counting_iterator<size_type>(num_strings),
-                   [col                = *col_device_view,
-                    d_strview_offsets  = d_strview_offsets.begin(),
-                    d_strviews         = d_strviews.begin(),
-                    labels             = labels->view().begin<size_type>(),
-                    list_offsets       = offsets.begin<size_type>(),
-                    d_strings_children = *d_strings_children,
-                    element_separator,
-                    element_narep] __device__(auto idx) {
-                     auto const label         = labels[idx];
-                     auto const sublist_index = idx - list_offsets[label];
-                     auto const strview_index = d_strview_offsets[label] + sublist_index * 2 + 1;
-                     // value or na_rep
-                     auto const strview = d_strings_children.element<cudf::string_view>(idx);
-                     d_strviews[strview_index] =
-                       d_strings_children.is_null(idx) ? element_narep : strview;
-                     // separator
-                     if (sublist_index != 0) { d_strviews[strview_index - 1] = element_separator; }
-                   });
+                   scatter_fn{*col_device_view,
+                              d_strview_offsets.data(),
+                              d_strviews.data(),
+                              labels->view().data<size_type>(),
+                              offsets.data<size_type>(),
+                              *d_strings_children,
+                              element_separator,
+                              element_narep});
 
   auto joined_col = make_strings_column(d_strviews, string_view{nullptr, 0}, stream, mr);
 

cpp/src/io/orc/orc.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2024, NVIDIA CORPORATION.
+ * Copyright (c) 2019-2025, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -707,7 +707,7 @@ struct orc_column_device_view : public column_device_view {
 struct rowgroup_rows {
   size_type begin;
   size_type end;
-  [[nodiscard]] constexpr auto size() const noexcept { return end - begin; }
+  [[nodiscard]] CUDF_HOST_DEVICE constexpr auto size() const noexcept { return end - begin; }
 };
 
 }  // namespace orc