Add per-frame linear memory allocator

src/core/CMakeLists.txt

@@ -1,3 +1,5 @@
 target_sources(SRB2SDL2 PRIVATE
+	memory.cpp
+	memory.h
 	static_vec.hpp
 )

src/core/memory.cpp

@@ -0,0 +1,70 @@
+// SONIC ROBO BLAST 2
+//-----------------------------------------------------------------------------
+// Copyright (C) 2023 by Ronald "Eidolon" Kinard
+//
+// This program is free software distributed under the
+// terms of the GNU General Public License, version 2.
+// See the 'LICENSE' file for more details.
+//-----------------------------------------------------------------------------
+
+#include "memory.h"
+
+#include <array>
+#include <new>
+
+#include "../z_zone.h"
+
+namespace
+{
+
+class LinearMemory
+{
+	size_t size_;
+	size_t height_;
+	void* memory_;
+
+public:
+	constexpr explicit LinearMemory(size_t size) noexcept;
+
+	void* allocate(size_t size);
+	void reset() noexcept;
+};
+
+constexpr LinearMemory::LinearMemory(size_t size) noexcept : size_(size), height_{0}, memory_{nullptr} {}
+
+void* LinearMemory::allocate(size_t size)
+{
+	size_t aligned_size = (size + 15) & ~15;
+	if (height_ + aligned_size > size_)
+	{
+		throw std::bad_alloc();
+	}
+
+	if (memory_ == nullptr)
+	{
+		memory_ = Z_Malloc(size_, PU_STATIC, nullptr);
+	}
+
+	void* ptr = (void*)((uintptr_t)(memory_) + height_);
+	height_ += aligned_size;
+	return ptr;
+}
+
+void LinearMemory::reset() noexcept
+{
+	height_ = 0;
+}
+
+} // namespace
+
+static LinearMemory g_frame_memory {4 * 1024 * 1024};
+
+void* Z_Frame_Alloc(size_t size)
+{
+	return g_frame_memory.allocate(size);
+}
+
+void Z_Frame_Reset()
+{
+	g_frame_memory.reset();
+}

src/core/memory.h

@@ -0,0 +1,31 @@
+// SONIC ROBO BLAST 2
+//-----------------------------------------------------------------------------
+// Copyright (C) 2023 by Ronald "Eidolon" Kinard
+//
+// This program is free software distributed under the
+// terms of the GNU General Public License, version 2.
+// See the 'LICENSE' file for more details.
+//-----------------------------------------------------------------------------
+
+#ifndef __SRB2_CORE_MEMORY_H__
+#define __SRB2_CORE_MEMORY_H__
+
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif // __cpluspplus
+
+/// @brief Allocate a block of memory with a lifespan of the current main-thread frame.
+/// This function is NOT thread-safe, but the allocated memory may be used across threads.
+/// @return a pointer to a block of memory aligned with libc malloc alignment, or null if allocation fails
+void* Z_Frame_Alloc(size_t size);
+
+/// @brief Resets per-frame memory. Not thread safe.
+void Z_Frame_Reset(void);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif // __cplusplus
+
+#endif // __SRB2_CORE_MEMORY_H__

src/d_main.cpp

@@ -72,6 +72,7 @@
 #include "filesrch.h" // refreshdirmenu
 #include "g_input.h" // tutorial mode control scheming
 #include "m_perfstats.h"
+#include "core/memory.h"
 
 #include "monocypher/monocypher.h"
 #include "stun.h"
@@ -821,6 +822,8 @@ void D_SRB2Loop(void)
 		precise_t enterprecise = I_GetPreciseTime();
 		precise_t finishprecise = enterprecise;
 
+		Z_Frame_Reset();
+
 		{
 			// Casting the return value of a function is bad practice (apparently)
 			double budget = round((1.0 / R_GetFramerateCap()) * I_GetPrecisePrecision());