Move morph_data::morph_times into a trailing allocation

Initially, this just makes the code more complicated.  In the end, it
will allow choosing the array size dynamically.

common/include/compiler-span.h

@@ -0,0 +1,46 @@
+/*
+ * This file is part of the DXX-Rebirth project <https://www.dxx-rebirth.com/>.
+ * It is copyright by its individual contributors, as recorded in the
+ * project's Git history.  See COPYING.txt at the top level for license
+ * terms and a link to the Git history.
+ */
+#pragma once
+
+#include <cstddef>
+
+/* Partial implementation of std::span (C++20) for pre-C++20 compilers.
+ * As of this writing, there are no released compilers with C++20
+ * support, so this implementation is always used.
+ *
+ * This implementation covers only the minimal functionality used by
+ * Rebirth.  It is not intended as a drop-in replacement for arbitrary
+ * use of std::span.
+ */
+
+template <typename T>
+class span
+{
+	std::size_t extent;
+	T *ptr;
+public:
+	span(T *p, std::size_t l) :
+		extent(l), ptr(p)
+	{
+	}
+	T *begin() const
+	{
+		return ptr;
+	}
+	T *end() const
+	{
+		return ptr + extent;
+	}
+	std::size_t size() const
+	{
+		return extent;
+	}
+	T &operator[](std::size_t i) const
+	{
+		return *(ptr + i);
+	}
+};

common/main/morph.h

@@ -35,6 +35,7 @@ COPYRIGHT 1993-1999 PARALLAX SOFTWARE CORPORATION.  ALL RIGHTS RESERVED.
 #include "compiler-array.h"
 
 #ifdef dsx
+#include "compiler-span.h"
 #include "fwd-object.h"
 #include <memory>
 
@@ -74,11 +75,11 @@ struct morph_data : prohibit_void_ptr<morph_data>
 	physics_info morph_save_phys_info;
 	array<submodel_state, MAX_SUBMODELS> submodel_active;         // which submodels are active
 	array<vms_vector, MAX_VECS> morph_vecs, morph_deltas;
-	array<fix, MAX_VECS> morph_times;
 	array<int, MAX_SUBMODELS>
 		n_morphing_points,       // how many active points in each part
 		submodel_startpoints;    // first point for each submodel
 	static ptr create(object_base &);
+	span<fix> get_morph_times();
 private:
 	static void *operator new(std::size_t bytes, max_vectors);
 	explicit morph_data(object_base &o);

similar/main/morph.cpp

@@ -99,8 +99,7 @@ submodel_data parse_model_data_header(const polymodel &pm, const unsigned submod
 
 void *morph_data::operator new(std::size_t, const max_vectors max_vecs)
 {
-	(void)max_vecs;
-	return ::operator new(sizeof(morph_data));
+	return ::operator new(sizeof(morph_data) + (max_vecs.count * sizeof(fix)));
 }
 
 morph_data::ptr morph_data::create(object_base &o)
@@ -114,11 +113,17 @@ morph_data::morph_data(object_base &o) :
 	DXX_POISON_VAR(submodel_active, 0xcc);
 	DXX_POISON_VAR(morph_vecs, 0xcc);
 	DXX_POISON_VAR(morph_deltas, 0xcc);
-	DXX_POISON_VAR(morph_times, 0xcc);
+	const auto morph_times = get_morph_times();
+	DXX_POISON_MEMORY(morph_times.begin(), morph_times.end(), 0xcc);
 	DXX_POISON_VAR(n_morphing_points, 0xcc);
 	DXX_POISON_VAR(submodel_startpoints, 0xcc);
 }
 
+span<fix> morph_data::get_morph_times()
+{
+	return {reinterpret_cast<fix *>(this + 1), MAX_VECS};
+}
+
 d_level_unique_morph_object_state::~d_level_unique_morph_object_state() = default;
 
 //returns ptr to data for this object, or NULL if none
@@ -214,11 +219,12 @@ static void init_points(const polymodel &pm, const vms_vector *const box_size, c
 	md->n_morphing_points[submodel_num] = 0;
 	md->submodel_startpoints[submodel_num] = startpoint;
 
+	const auto morph_times = md->get_morph_times();
 	auto &&zr = zip(
 		unchecked_partial_range(reinterpret_cast<const vms_vector *>(sd.body), sd.nverts),
 		partial_range(md->morph_vecs, startpoint, endpoint),
 		partial_range(md->morph_deltas, startpoint, endpoint),
-		partial_range(md->morph_times, startpoint, endpoint)
+		partial_range(morph_times, startpoint, endpoint)
 	);
 	range_for (auto &&z, zr)
 	{
@@ -249,11 +255,12 @@ static void update_points(const polymodel &pm, const unsigned submodel_num, morp
 	const unsigned startpoint = sd.startpoint;
 	const unsigned endpoint = startpoint + sd.nverts;
 
+	const auto morph_times = md->get_morph_times();
 	auto &&zr = zip(
 		unchecked_partial_range(reinterpret_cast<const vms_vector *>(sd.body), sd.nverts),
 		partial_range(md->morph_vecs, startpoint, endpoint),
 		partial_range(md->morph_deltas, startpoint, endpoint),
-		partial_range(md->morph_times, startpoint, endpoint)
+		partial_range(morph_times, startpoint, endpoint)
 	);
 	range_for (auto &&z, zr)
 	{
@@ -384,7 +391,8 @@ void morph_start(d_level_unique_morph_object_state &LevelUniqueMorphObjectState,
 	box_size.z = max(-pmmin.z,pmmax.z) / 2;
 
 	//clear all points
-	md->morph_times = {};
+	const auto morph_times = md->get_morph_times();
+	std::fill(morph_times.begin(), morph_times.end(), fix());
 	//clear all parts
 	md->submodel_active = {};