Add missing `scalar_type.hpp`

core/scalar_type.hpp

@@ -0,0 +1,347 @@
+#pragma once
+
+// For TORCH_CHECK
+#include <torch/library.h>
+
+namespace vllm {
+
+//
+//  ScalarType can represent a wide range of floating point and integer types,
+//  in particular it can be used to represent sub-byte data types (something
+//  that torch.dtype currently does not support).
+//
+//  The type definitions on the Python side can be found in: vllm/scalar_type.py
+//  these type definitions should be kept up to date with any Python API changes
+//  here.
+//
+class ScalarType {
+ public:
+  enum NanRepr : uint8_t {
+    NAN_NONE = 0,                // nans are not supported
+    NAN_IEEE_754 = 1,            // nans are: exp all 1s, mantissa not all 0s
+    NAN_EXTD_RANGE_MAX_MIN = 2,  // nans are: exp all 1s, mantissa all 1s
+
+    NAN_REPR_ID_MAX
+  };
+
+  constexpr ScalarType(uint8_t exponent, uint8_t mantissa, bool signed_,
+                       int32_t bias, bool finite_values_only = false,
+                       NanRepr nan_repr = NAN_IEEE_754)
+      : exponent(exponent),
+        mantissa(mantissa),
+        signed_(signed_),
+        bias(bias),
+        finite_values_only(finite_values_only),
+        nan_repr(nan_repr){};
+
+  static constexpr ScalarType int_(uint8_t size_bits, int32_t bias = 0) {
+    return ScalarType(0, size_bits - 1, true, bias);
+  }
+
+  static constexpr ScalarType uint(uint8_t size_bits, int32_t bias = 0) {
+    return ScalarType(0, size_bits, false, bias);
+  }
+
+  // IEEE 754 compliant floating point type
+  static constexpr ScalarType float_IEEE754(uint8_t exponent,
+                                            uint8_t mantissa) {
+    TORCH_CHECK(mantissa > 0 && exponent > 0);
+    return ScalarType(exponent, mantissa, true, 0, false, NAN_IEEE_754);
+  }
+
+  // IEEE 754 non-compliant floating point type
+  static constexpr ScalarType float_(uint8_t exponent, uint8_t mantissa,
+                                     bool finite_values_only,
+                                     NanRepr nan_repr) {
+    TORCH_CHECK(nan_repr < NAN_REPR_ID_MAX, "Invalid NanRepr");
+    TORCH_CHECK(mantissa > 0 && exponent > 0);
+    TORCH_CHECK(nan_repr != NAN_IEEE_754,
+                "use `float_IEEE754` constructor for floating point types that "
+                "follow IEEE 754 conventions");
+    return ScalarType(exponent, mantissa, true, 0, finite_values_only,
+                      nan_repr);
+  }
+
+  uint8_t const exponent;  // size of the exponent field (0 for integer types)
+  uint8_t const mantissa;  // size of the mantissa field (size of the integer
+                           // excluding the sign bit for integer types)
+  bool const signed_;  // flag if the type supports negative numbers (i.e. has a
+                       // sign bit)
+  int32_t const bias;  // stored values equal value + bias,
+                       // used for quantized type
+
+  // Extra Floating point info
+  bool const finite_values_only;  // i.e. no +/-inf if true
+  NanRepr const nan_repr;         // how NaNs are represented
+                                  // (not applicable for integer types)
+
+  using Id = int64_t;
+
+ private:
+  // Field size in id
+  template <typename T_>
+  static constexpr size_t member_id_field_width() {
+    using T = std::decay_t<T_>;
+    return std::is_same_v<T, bool> ? 1 : sizeof(T) * 8;
+  }
+
+  template <typename Fn, typename Init, typename Member, typename... Rest>
+  static constexpr auto reduce_members_helper(Fn f, Init val, Member member,
+                                              Rest... rest) {
+    auto new_val = f(val, member);
+    if constexpr (sizeof...(rest) > 0) {
+      return reduce_members_helper(f, new_val, rest...);
+    } else {
+      return new_val;
+    };
+  }
+
+  template <typename Fn, typename Init>
+  constexpr auto reduce_members(Fn f, Init init) const {
+    // Should be in constructor order for `from_id`
+    return reduce_members_helper(f, init, exponent, mantissa, signed_, bias,
+                                 finite_values_only, nan_repr);
+  };
+
+  template <typename Fn, typename Init>
+  static constexpr auto reduce_member_types(Fn f, Init init) {
+    constexpr auto dummy_type = ScalarType(0, 0, false, 0, false, NAN_NONE);
+    return dummy_type.reduce_members(f, init);
+  };
+
+  static constexpr auto id_size_bits() {
+    return reduce_member_types(
+        [](int acc, auto member) -> int {
+          return acc + member_id_field_width<decltype(member)>();
+        },
+        0);
+  }
+
+ public:
+  // unique id for this scalar type that can be computed at compile time for
+  //  c++17 template specialization this is not needed once we migrate to
+  //  c++20 and can pass literal classes as template parameters
+  constexpr Id id() const {
+    static_assert(id_size_bits() <= sizeof(Id) * 8,
+                  "ScalarType id is too large to be stored");
+
+    auto or_and_advance = [](std::pair<Id, uint32_t> result,
+                             auto member) -> std::pair<Id, uint32_t> {
+      auto [id, bit_offset] = result;
+      auto constexpr bits = member_id_field_width<decltype(member)>();
+      return {id | (int64_t(member) & ((uint64_t(1) << bits) - 1))
+                       << bit_offset,
+              bit_offset + bits};
+    };
+    return reduce_members(or_and_advance, std::pair<Id, uint32_t>{}).first;
+  }
+
+  // create a ScalarType from an id, for c++17 template specialization,
+  //  this is not needed once we migrate to c++20 and can pass literal
+  //  classes as template parameters
+  static constexpr ScalarType from_id(Id id) {
+    auto extract_and_advance = [id](auto result, auto member) {
+      using T = decltype(member);
+      auto [tuple, bit_offset] = result;
+      auto constexpr bits = member_id_field_width<T>();
+      auto extracted_val = static_cast<T>((int64_t(id) >> bit_offset) &
+                                          ((uint64_t(1) << bits) - 1));
+      auto new_tuple = std::tuple_cat(tuple, std::make_tuple(extracted_val));
+      return std::pair<decltype(new_tuple), int>{new_tuple, bit_offset + bits};
+    };
+
+    auto [tuple_args, _] = reduce_member_types(extract_and_advance,
+                                               std::pair<std::tuple<>, int>{});
+    return std::apply([](auto... args) { return ScalarType(args...); },
+                      tuple_args);
+  }
+
+  constexpr int64_t size_bits() const {
+    return mantissa + exponent + is_signed();
+  }
+  constexpr bool is_signed() const { return signed_; }
+  constexpr bool is_integer() const { return exponent == 0; }
+  constexpr bool is_floating_point() const { return exponent > 0; }
+  constexpr bool is_ieee_754() const {
+    return is_floating_point() && finite_values_only == false &&
+           nan_repr == NAN_IEEE_754;
+  }
+  constexpr bool has_nans() const {
+    return is_floating_point() && nan_repr != NAN_NONE;
+  }
+  constexpr bool has_infs() const {
+    return is_floating_point() && finite_values_only == false;
+  }
+  constexpr bool has_bias() const { return bias != 0; }
+
+ private:
+  double _floating_point_max() const {
+    TORCH_CHECK(mantissa <= 52 && exponent <= 11,
+                "Cannot represent max/min as a double for type ", str());
+
+    uint64_t max_mantissa = (uint64_t(1) << mantissa) - 1;
+    if (nan_repr == NAN_EXTD_RANGE_MAX_MIN) {
+      max_mantissa -= 1;
+    }
+
+    uint64_t max_exponent = (uint64_t(1) << exponent) - 2;
+    if (nan_repr == NAN_EXTD_RANGE_MAX_MIN || nan_repr == NAN_NONE) {
+      TORCH_CHECK(exponent < 11,
+                  "Cannot represent max/min as a double for type ", str());
+      max_exponent += 1;
+    }
+
+    // adjust the exponent to match that of a double
+    //  for now we assume the exponent bias is the standard 2^(e-1) -1, (where e
+    //  is the exponent bits), there is some precedent for non-standard biases,
+    //  example `float8_e4m3b11fnuz` here: https://github.com/jax-ml/ml_dtypes
+    //  but to avoid premature over complication we are just assuming the
+    //  standard exponent bias until there is a need to support non-standard
+    //  biases
+    uint64_t exponent_bias = (uint64_t(1) << (exponent - 1)) - 1;
+    uint64_t exponent_bias_double = (uint64_t(1) << 10) - 1;  // double e = 11
+
+    uint64_t max_exponent_double =
+        max_exponent - exponent_bias + exponent_bias_double;
+
+    // shift the mantissa into the position for a double and
+    // the exponent
+    uint64_t double_raw =
+        (max_mantissa << (52 - mantissa)) | (max_exponent_double << 52);
+
+    return *reinterpret_cast<double*>(&double_raw);
+  }
+
+  constexpr std::variant<int64_t, double> _raw_max() const {
+    if (is_floating_point()) {
+      return {_floating_point_max()};
+    } else {
+      TORCH_CHECK(size_bits() < 64 || size_bits() == 64 && is_signed(),
+                  "Cannot represent max as a int64_t");
+      return {(int64_t(1) << mantissa) - 1};
+    }
+  }
+
+  constexpr std::variant<int64_t, double> _raw_min() const {
+    if (is_floating_point()) {
+      TORCH_CHECK(is_signed(),
+                  "We currently assume all floating point types are signed");
+      constexpr uint64_t sign_bit_double = (uint64_t(1) << 63);
+
+      double max = _floating_point_max();
+      uint64_t max_raw = *reinterpret_cast<uint64_t*>(&max);
+      uint64_t min_raw = max_raw | sign_bit_double;
+      return {*reinterpret_cast<double*>(&min_raw)};
+    } else {
+      TORCH_CHECK(!is_signed() || size_bits() <= 64,
+                  "Cannot represent min as a int64_t");
+      if (is_signed()) {
+        // set the top bit to 1 (i.e. INT64_MIN) and the rest to 0
+        // then perform an arithmetic shift right to set all the bits above
+        // (size_bits() - 1) to 1
+        return {INT64_MIN >> (64 - size_bits())};
+      } else {
+        return {int64_t(0)};
+      }
+    }
+  }
+
+ public:
+  // Max representable value for this scalar type.
+  // (accounting for bias if there is one)
+  constexpr std::variant<int64_t, double> max() const {
+    return std::visit(
+        [this](auto x) -> std::variant<int64_t, double> { return {x - bias}; },
+        _raw_max());
+  }
+
+  // Min representable value for this scalar type.
+  // (accounting for bias if there is one)
+  constexpr std::variant<int64_t, double> min() const {
+    return std::visit(
+        [this](auto x) -> std::variant<int64_t, double> { return {x - bias}; },
+        _raw_min());
+  }
+
+  std::string str() const {
+    /* naming generally follows: https://github.com/jax-ml/ml_dtypes
+     * for floating point types (leading f) the scheme is:
+     *  `float<size_bits>_e<exponent_bits>m<mantissa_bits>[flags]`
+     *  flags:
+     *  - no-flags: means it follows IEEE 754 conventions
+     *  - f: means finite values only (no infinities)
+     *  - n: means nans are supported (non-standard encoding)
+     * for integer types the scheme is:
+     *  `[u]int<size_bits>[b<bias>]`
+     *  - if bias is not present it means its zero
+     */
+    if (is_floating_point()) {
+      auto ret = "float" + std::to_string(size_bits()) + "_e" +
+                 std::to_string(exponent) + "m" + std::to_string(mantissa);
+      if (!is_ieee_754()) {
+        if (finite_values_only) {
+          ret += "f";
+        }
+        if (nan_repr != NAN_NONE) {
+          ret += "n";
+        }
+      }
+      return ret;
+    } else {
+      auto ret = ((is_signed()) ? "int" : "uint") + std::to_string(size_bits());
+      if (has_bias()) {
+        ret += "b" + std::to_string(bias);
+      }
+      return ret;
+    }
+  }
+
+  constexpr bool operator==(ScalarType const& other) const {
+    return mantissa == other.mantissa && exponent == other.exponent &&
+           bias == other.bias && signed_ == other.signed_ &&
+           finite_values_only == other.finite_values_only &&
+           nan_repr == other.nan_repr;
+  }
+};
+
+using ScalarTypeId = ScalarType::Id;
+
+// "rust style" names generally following:
+//   https://github.com/pytorch/pytorch/blob/6d9f74f0af54751311f0dd71f7e5c01a93260ab3/torch/csrc/api/include/torch/types.h#L60-L70
+static inline constexpr auto kS4 = ScalarType::int_(4);
+static inline constexpr auto kU4 = ScalarType::uint(4);
+static inline constexpr auto kU4B8 = ScalarType::uint(4, 8);
+static inline constexpr auto kS8 = ScalarType::int_(8);
+static inline constexpr auto kU8 = ScalarType::uint(8);
+static inline constexpr auto kU8B128 = ScalarType::uint(8, 128);
+
+static inline constexpr auto kFE3M2f =
+    ScalarType::float_(3, 2, true, ScalarType::NAN_NONE);
+static inline constexpr auto kFE4M3fn =
+    ScalarType::float_(4, 3, true, ScalarType::NAN_EXTD_RANGE_MAX_MIN);
+static inline constexpr auto kFE5M2 = ScalarType::float_IEEE754(5, 2);
+static inline constexpr auto kFE8M7 = ScalarType::float_IEEE754(8, 7);
+static inline constexpr auto kFE5M10 = ScalarType::float_IEEE754(5, 10);
+
+// Fixed width style names, generally following:
+//  https://github.com/pytorch/pytorch/blob/6d9f74f0af54751311f0dd71f7e5c01a93260ab3/torch/csrc/api/include/torch/types.h#L47-L57
+static inline constexpr auto kInt4 = kS4;
+static inline constexpr auto kUint4 = kU4;
+static inline constexpr auto kUint4b8 = kU4B8;
+static inline constexpr auto kInt8 = kS8;
+static inline constexpr auto kUint8 = kU8;
+static inline constexpr auto kUint8b128 = kU8B128;
+
+static inline constexpr auto kFloat6_e3m2f = kFE3M2f;
+static inline constexpr auto kFloat8_e4m3fn = kFE4M3fn;
+static inline constexpr auto kFloat8_e5m2 = kFE5M2;
+static inline constexpr auto kFloat16_e8m7 = kFE8M7;
+static inline constexpr auto kFloat16_e5m10 = kFE5M10;
+
+// colloquial names
+static inline constexpr auto kHalf = kFE5M10;
+static inline constexpr auto kFloat16 = kHalf;
+static inline constexpr auto kBFloat16 = kFE8M7;
+
+static inline constexpr auto kFloat16Id = kFloat16.id();
+};  // namespace vllm