From dfff5028f3f7baee4e764744a656baf553bc4b70 Mon Sep 17 00:00:00 2001
From: Richard Thier <magosit@outlook.hu>
Date: Tue, 22 Oct 2024 11:49:03 +0200
Subject: [PATCH] added freearena(..) because it was really needed - untested,
 but probably good

---
 arena.h | 100 +++++++++++++++++++++++++++++++-------------------------
 1 file changed, 55 insertions(+), 45 deletions(-)

diff --git a/arena.h b/arena.h
index ecafbda..d824b63 100644
--- a/arena.h
+++ b/arena.h
@@ -16,88 +16,98 @@
 
 static void *os_reserve(ptrdiff_t);
 static char os_commit(void *, ptrdiff_t);
+static char os_free(void *, ptrdiff_t);
 
 #define ARENA_PAGESIZE ((ptrdiff_t)1<<26)
 
 typedef struct {
-    char *begin;
-    char *commit;
-    char *end;
+	char *begin;
+	char *commit;
+	char *end;
 } arena;
 
-static arena newarena(ptrdiff_t cap)
-{
-    arena a = {0};
-    cap += -cap & (ARENA_PAGESIZE - 1);
-    a.begin = a.commit = a.end = (char*) os_reserve(cap);
-    if (a.begin) {
-        a.end += cap;
-    }
-    return a;
+static inline arena newarena(ptrdiff_t cap) {
+	arena a = {0};
+	cap += -cap & (ARENA_PAGESIZE - 1);
+	a.begin = a.commit = a.end = (char*) os_reserve(cap);
+	if (a.begin) {
+		a.end += cap;
+	}
+	return a;
 }
 
-static void *aralloc(arena *a, ptrdiff_t size, ptrdiff_t align, ptrdiff_t count)
-{
-    ptrdiff_t padding   = -(size_t)a->begin & (align - 1);
-    ptrdiff_t committed = a->commit - a->begin;
-    if (count > (committed-padding)/size) {
-        ptrdiff_t reserved = a->end - a->begin;
-        if (count > (reserved-padding)/size) {
-            return 0;
-        }
+static inline void *aralloc(arena *a, ptrdiff_t size, ptrdiff_t align, ptrdiff_t count) {
+	ptrdiff_t padding   = -(size_t)a->begin & (align - 1);
+	ptrdiff_t committed = a->commit - a->begin;
+	if (count > (committed-padding)/size) {
+		ptrdiff_t reserved = a->end - a->begin;
+		if (count > (reserved-padding)/size) {
+			return 0;
+		}
 
-        ptrdiff_t needed = size*count + padding - committed;
-        needed += -needed & (ARENA_PAGESIZE - 1);
-        if (!os_commit(a->commit, needed)) {
-            return 0;
-        }
-        a->commit += needed;
-    }
+		ptrdiff_t needed = size*count + padding - committed;
+		needed += -needed & (ARENA_PAGESIZE - 1);
+		if (!os_commit(a->commit, needed)) {
+			return 0;
+		}
+		a->commit += needed;
+	}
 
-    void *ptr = a->begin + padding;
-    a->begin += padding + size*count;
+	void *ptr = a->begin + padding;
+	a->begin += padding + size*count;
 
 	// Change to this instead if you want zero-inited (but this gets slow with many arenas)
-    //return memset(ptr, 0, size*count);
+	//return memset(ptr, 0, size*count);
 	return ptr;
 }
 
+/** Removes an arena (fully) */
+static inline char freearena(arena *a) {
+	return os_free(a->begin, (a->end) - (a->begin));
+}
+
 #ifdef _WIN32
 // $ cc -g3 -nostartfiles -o arena.exe arena.c
 // $ cl /Z7 arena.c /link /subsystem:console kernel32.lib libvcruntime.lib
 #define W32(r) __declspec(dllimport) r __stdcall
 W32(void)   ExitProcess(int);
 W32(void *) VirtualAlloc(void *, ptrdiff_t, int, int);
+W32(void *) VirtualFree(void *, ptrdiff_t, int);
 
 #define MEM_COMMIT     0x1000
 #define MEM_RESERVE    0x2000
 #define PAGE_NOACCESS  0x0001
 #define PAGE_READWRITE 0x0004
+#define MEM_RELEASE    0x8000
 
-static void *os_reserve(ptrdiff_t cap)
-{
-    return VirtualAlloc(0, cap, MEM_RESERVE, PAGE_NOACCESS);
+static void *os_reserve(ptrdiff_t cap) {
+	return VirtualAlloc(0, cap, MEM_RESERVE, PAGE_NOACCESS);
 }
 
-static char os_commit(void *ptr, ptrdiff_t len)
-{
-    return VirtualAlloc(ptr, len, MEM_COMMIT, PAGE_READWRITE);
+static char os_commit(void *ptr, ptrdiff_t len) {
+	return VirtualAlloc(ptr, len, MEM_COMMIT, PAGE_READWRITE);
+}
+
+static char os_free(void *ptr, ptrdiff_t len) {
+	return VirtualFree(ptr, len, MEM_RELEASE);
 }
 
 #else  // POSIX
-// $ cc -g3 -o arena arena.c
 #include <sys/mman.h>
 
-static void *os_reserve(ptrdiff_t cap)
-{
-    void *r = mmap(0, cap, PROT_NONE, MAP_ANON|MAP_PRIVATE, -1, 0);
-    return r==MAP_FAILED ? 0 : r;
+static void *os_reserve(ptrdiff_t cap) {
+	void *r = mmap(0, cap, PROT_NONE, MAP_ANON|MAP_PRIVATE, -1, 0);
+	return r==MAP_FAILED ? 0 : r;
 }
 
-static char os_commit(void *ptr, ptrdiff_t len)
-{
-    return !mprotect(ptr, len, PROT_READ|PROT_WRITE);
+static char os_commit(void *ptr, ptrdiff_t len) {
+	return !mprotect(ptr, len, PROT_READ|PROT_WRITE);
 }
+
+static char os_free(void *ptr, ptrdiff_t len) {
+	return !munmap(ptr, len);
+}
+
 #endif // POSIX
 
 #endif /* ARENA_H */