Allow compile-time casts

1 files changed, 239 insertions, 40 deletions

diff --git a/boot/evaluator.cc b/boot/evaluator.cc
index 6a9fb3b..b1648af 100644
--- a/boot/evaluator.cc
+++ b/boot/evaluator.cc
@@ -19,6 +19,7 @@ along with GCC; see the file COPYING3.  If not see
 
 #include "elna/boot/ast.h"
 
+#include <cmath>
 #include <cstddef>
 #include <limits>
 #include <ranges>
@@ -680,28 +681,130 @@ namespace elna::boot
         }, lhs.value());
     }
 
-    std::optional<constant_value> evaluator::cast_to_int(const constant_value& source_expression)
+    static std::optional<constant_value> integer_constant(const bool target_signed,
+            const std::size_t target_size, const double value)
     {
-        return std::visit([](auto&& source_value) -> std::optional<constant_value> {
+        std::optional<integer_literal> result =
+            integer_literal::from(target_size, static_cast<std::size_t>(std::abs(value)));
+
+        if (result.has_value() && value < 0.0)
+        {
+            result = result.value().negate();
+        }
+        if (!result.has_value() || !result.value().fit_into(target_signed, target_size))
+        {
+            return std::nullopt;
+        }
+        return constant_value{ std::move(result).value() };
+    }
+
+    /// The caller converts the result, so the range is checked here rather than
+    /// left to an out of range floating point to integer conversion.
+    static std::optional<double> truncate_into(const float_literal& source_value,
+            const bool target_signed, const std::size_t target_size)
+    {
+        if (!source_value.is_finite())
+        {
+            return std::nullopt;
+        }
+        const double truncated = std::trunc(source_value.value());
+        const int value_bits = static_cast<int>(target_size * CHAR_BIT) - (target_signed ? 1 : 0);
+        const double bound = std::ldexp(1.0, value_bits);
+
+        if (truncated >= bound || truncated < (target_signed ? -bound : 0.0))
+        {
+            return std::nullopt;
+        }
+        return truncated;
+    }
+
+    static std::optional<double> widen_to_double(const integer_literal& source_value)
+    {
+        if (source_value.is_signed())
+        {
+            std::optional<std::ptrdiff_t> signed_value = source_value.try_to<std::ptrdiff_t>();
+
+            return signed_value.has_value()
+                ? std::optional(static_cast<double>(signed_value.value()))
+                : std::nullopt;
+        }
+        std::optional<std::size_t> unsigned_value = source_value.try_to<std::size_t>();
+
+        return unsigned_value.has_value()
+            ? std::optional(static_cast<double>(unsigned_value.value()))
+            : std::nullopt;
+    }
+
+    std::optional<constant_value> evaluator::cast_to_integer(const constant_value& source_expression,
+            const bool target_signed, const std::size_t target_size)
+    {
+        return std::visit([target_signed, target_size](auto&& source_value) -> std::optional<constant_value> {
             using T = std::decay_t<decltype(source_value)>;
 
             if constexpr (std::is_same_v<T, integer_literal>)
             {
-                std::optional<std::ptrdiff_t> signed_value = source_value.template try_to<std::ptrdiff_t>();
+                // Changing the signedness without changing the width
+                // reinterprets the bits and loses nothing.
+                if (source_value.size() == target_size)
+                {
+                    return constant_value{ source_value.cast_to(target_signed, target_size) };
+                }
+                integer_literal narrowed = source_value;
+
+                return narrowed.fit_into(target_signed, target_size)
+                    ? std::optional(constant_value{ std::move(narrowed) })
+                    : std::nullopt;
+            }
+            else if constexpr (std::is_same_v<T, float_literal>)
+            {
+                std::optional<double> truncated = truncate_into(source_value, target_signed, target_size);
+
+                return truncated.has_value()
+                    ? integer_constant(target_signed, target_size, truncated.value())
+                    : std::nullopt;
+            }
+            else if constexpr (std::is_same_v<T, bool> || std::is_same_v<T, std::uint32_t>)
+            {
+                return integer_constant(target_signed, target_size, static_cast<double>(source_value));
+            }
+            else if constexpr (std::is_same_v<T, std::nullptr_t>)
+            {
+                return integer_constant(target_signed, target_size, 0.0);
+            }
+            else
+            {
+                return std::nullopt;
+            }
+        }, source_expression);
+    }
+
+    std::optional<constant_value> evaluator::cast_to_float(const constant_value& source_expression,
+            const float_literal::format_kind target_format)
+    {
+        return std::visit([target_format](auto&& source_value) -> std::optional<constant_value> {
+            using T = std::decay_t<decltype(source_value)>;
+
+            if constexpr (std::is_same_v<T, float_literal>)
+            {
+                return constant_value{ source_value.cast_to(target_format) };
+            }
+            else if constexpr (std::is_same_v<T, integer_literal>)
+            {
+                std::optional<double> widened = widen_to_double(source_value);
 
-                return signed_value.has_value()
-                    ? std::optional(integer_literal::from(signed_value.value()))
+                return widened.has_value()
+                    ? std::optional(constant_value{ float_literal::from(widened.value()).cast_to(target_format) })
                     : std::nullopt;
             }
-            else if constexpr (std::is_same_v<T, double>
-                    || std::is_same_v<T, bool>
-                    || std::is_same_v<T, std::uint32_t>)
+            else if constexpr (std::is_same_v<T, bool> || std::is_same_v<T, std::uint32_t>)
             {
-                return integer_literal::from(static_cast<std::ptrdiff_t>(source_value));
+                const float_literal widened = float_literal::from(static_cast<double>(source_value));
+
+                return constant_value{ widened.cast_to(target_format) };
             }
             else if constexpr (std::is_same_v<T, std::nullptr_t>)
             {
-                return integer_literal::from<std::ptrdiff_t>(0);
+                return constant_value{ float_literal::from(0.0).cast_to(target_format) };
             }
             else
             {
@@ -710,28 +813,70 @@ namespace elna::boot
         }, source_expression);
     }
 
-    std::optional<constant_value> evaluator::cast_to_word(const constant_value& source_expression)
+    std::optional<constant_value> evaluator::cast_to_bool(const constant_value& source_expression)
     {
         return std::visit([](auto&& source_value) -> std::optional<constant_value> {
             using T = std::decay_t<decltype(source_value)>;
 
-            if constexpr (std::is_same_v<T, integer_literal>)
+            if constexpr (std::is_same_v<T, bool>)
+            {
+                return constant_value{ source_value };
+            }
+            else if constexpr (std::is_same_v<T, integer_literal>)
+            {
+                return constant_value{ !(source_value == std::ptrdiff_t{ 0 }) };
+            }
+            else if constexpr (std::is_same_v<T, float_literal>)
+            {
+                return constant_value{ !(source_value == 0.0) };
+            }
+            else if constexpr (std::is_same_v<T, std::uint32_t>)
+            {
+                return constant_value{ source_value != 0U };
+            }
+            else if constexpr (std::is_same_v<T, std::nullptr_t>)
+            {
+                return constant_value{ false };
+            }
+            else
+            {
+                return std::nullopt;
+            }
+        }, source_expression);
+    }
+
+    std::optional<constant_value> evaluator::cast_to_char(const constant_value& source_expression)
+    {
+        return std::visit([](auto&& source_value) -> std::optional<constant_value> {
+            using T = std::decay_t<decltype(source_value)>;
+
+            if constexpr (std::is_same_v<T, std::uint32_t>)
+            {
+                return constant_value{ source_value };
+            }
+            else if constexpr (std::is_same_v<T, integer_literal>)
+            {
+                std::optional<std::uint32_t> code_point = source_value.template try_to<std::uint32_t>();
+
+                return code_point.has_value()
+                    ? std::optional(constant_value{ code_point.value() })
+                    : std::nullopt;
+            }
+            else if constexpr (std::is_same_v<T, float_literal>)
             {
-                std::optional<std::size_t> unsigned_value = source_value.template try_to<std::size_t>();
+                std::optional<double> truncated = truncate_into(source_value, false, sizeof(std::uint32_t));
 
-                return unsigned_value.has_value()
-                    ? std::optional(integer_literal::from(unsigned_value.value()))
+                return truncated.has_value()
+                    ? std::optional(constant_value{ static_cast<std::uint32_t>(truncated.value()) })
                     : std::nullopt;
             }
-            else if constexpr (std::is_same_v<T, double>
-                    || std::is_same_v<T, bool>
-                    || std::is_same_v<T, std::uint32_t>)
+            else if constexpr (std::is_same_v<T, bool>)
             {
-                return integer_literal::from(static_cast<std::size_t>(source_value));
+                return constant_value{ static_cast<std::uint32_t>(source_value) };
             }
             else if constexpr (std::is_same_v<T, std::nullptr_t>)
             {
-                return integer_literal::from<std::ptrdiff_t>(0U);
+                return constant_value{ std::uint32_t{ 0 } };
             }
             else
             {
@@ -740,39 +885,93 @@ namespace elna::boot
         }, source_expression);
     }
 
+    std::optional<constant_value> evaluator::cast_to_enumeration(const constant_value& source_expression,
+            const std::size_t member_count, const std::size_t target_size)
+    {
+        std::optional<constant_value> position = cast_to_integer(source_expression, false, target_size);
+
+        if (!position.has_value())
+        {
+            return std::nullopt;
+        }
+        const auto *converted = std::get_if<integer_literal>(&position.value());
+
+        if (converted == nullptr || *converted < std::size_t{ 1 } || *converted > member_count)
+        {
+            return std::nullopt;
+        }
+        return position;
+    }
+
+    std::optional<constant_value> evaluator::cast_to_pointer(const constant_value& source_expression)
+    {
+        if (std::holds_alternative<std::nullptr_t>(source_expression))
+        {
+            return source_expression;
+        }
+        if (const auto *address = std::get_if<integer_literal>(&source_expression))
+        {
+            // Only the null pointer has a constant representation.
+            if (*address == std::ptrdiff_t{ 0 })
+            {
+                return constant_value{ nullptr };
+            }
+        }
+        return std::nullopt;
+    }
+
     std::optional<constant_value> evaluator::evaluate_cast(cast_expression& subject)
     {
-        auto value = evaluate(subject.value());
+        std::optional<constant_value> value = evaluate(subject.value());
 
         if (!value.has_value())
         {
             return std::nullopt;
         }
-        // The target type is looked up in the symbol table instead of reading
-        // the type decoration set by name analysis.
-        if (auto *target = subject.target().is_named())
+        const type source_type = resolve_underlying_type(subject.value().type_decoration);
+        const type target_type = resolve_underlying_type(subject.type_decoration);
+
+        if (source_type == target_type)
+        {
+            return value;
+        }
+        if (const std::shared_ptr<enumeration_type> enumeration = target_type.get<enumeration_type>())
         {
-            auto symbol = this->bag.lookup(target->name);
+            std::optional<type_properties> properties = get_type_properties(target_type, this->target);
 
-            if (symbol != nullptr)
+            if (!properties.has_value())
             {
-                if (auto type_symbol = symbol->is_type())
-                {
-                    const type resolved = resolve_underlying_type(type_symbol->symbol);
-
-                    if (is_primitive_type(resolved, "Int"))
-                    {
-                        return cast_to_int(value.value());
-                    }
-                    else if (is_primitive_type(resolved, "Word"))
-                    {
-                        return cast_to_word(value.value());
-                    }
-                }
+                return std::nullopt;
             }
+            return cast_to_enumeration(value.value(), enumeration->members.size(), properties->size);
         }
+        if (is_integral_type(target_type))
+        {
+            std::optional<type_properties> properties = get_type_properties(target_type, this->target);
 
-        return constant_value{ value.value() };
+            return properties.has_value()
+                ? cast_to_integer(value.value(), is_integer_type(target_type), properties->size)
+                : std::nullopt;
+        }
+        if (is_float_type(target_type))
+        {
+            return cast_to_float(value.value(), is_primitive_type(target_type, "Single")
+                    ? float_literal::format_kind::binary32
+                    : float_literal::format_kind::binary64);
+        }
+        if (is_primitive_type(target_type, "Bool"))
+        {
+            return cast_to_bool(value.value());
+        }
+        if (is_primitive_type(target_type, "Char"))
+        {
+            return cast_to_char(value.value());
+        }
+        if (is_any_pointer_type(target_type))
+        {
+            return cast_to_pointer(value.value());
+        }
+        return std::nullopt;
     }
 
     std::optional<std::size_t> evaluator::evaluate_traits_size(const type& subject)