From 0bb141777055f0ed1e8403ca426ac3e4304830e0 Mon Sep 17 00:00:00 2001
From: luboslenco <lubos.lenco@gmail.com>
Date: Mon, 23 Sep 2024 22:15:36 +0200
Subject: [PATCH] Add gc_cut

---
 sources/iron_gc.c |  7 +++++++
 sources/iron_gc.h |  1 +
 sources/libs/gc.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++-
 sources/libs/gc.h |  1 +
 4 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/sources/iron_gc.c b/sources/iron_gc.c
index a2609f61..4e8ae969 100644
--- a/sources/iron_gc.c
+++ b/sources/iron_gc.c
@@ -32,6 +32,9 @@ void gc_root(void *ptr) {
 void gc_unroot(void *ptr) {
 }
 
+void *gc_cut(void *ptr, size_t pos, size_t size) {
+}
+
 void *gc_realloc(void *ptr, size_t size) {
 	#ifdef HEAP_SIZE
 	// NOTE: gc_realloc is not implemented when HEAP_SIZE is defined
@@ -90,6 +93,10 @@ void gc_unroot(void *ptr) {
 	_gc_unroot(ptr);
 }
 
+void *gc_cut(void *ptr, size_t pos, size_t size) {
+	_gc_cut(ptr, pos, size);
+}
+
 void *gc_realloc(void *ptr, size_t size) {
 	return ptr == NULL ? gc_alloc(size) : _gc_realloc(ptr, size);
 }
diff --git a/sources/iron_gc.h b/sources/iron_gc.h
index 5d1167a0..d9962576 100644
--- a/sources/iron_gc.h
+++ b/sources/iron_gc.h
@@ -10,6 +10,7 @@ void gc_array(void *ptr, int *length);
 void gc_leaf(void *ptr);
 void gc_root(void *ptr);
 void gc_unroot(void *ptr);
+void *gc_cut(void *ptr, size_t pos, size_t size);
 void *gc_realloc(void *ptr, size_t size);
 void gc_free(void *ptr);
 void gc_pause();
diff --git a/sources/libs/gc.c b/sources/libs/gc.c
index bff9d112..718e4588 100644
--- a/sources/libs/gc.c
+++ b/sources/libs/gc.c
@@ -36,6 +36,7 @@
 #define GC_TAG_LEAF 0x1
 #define GC_TAG_MARK 0x2
 #define GC_TAG_ROOT 0x4
+#define GC_TAG_CUT 0x8
 
 #if defined(_MSC_VER) && !defined(__clang__)
 #define __builtin_frame_address(x)  ((void)(x), _AddressOfReturnAddress())
@@ -47,7 +48,8 @@ typedef struct gc_allocation {
 	int *array_length; // if this alloc is an array
 	char tag; // the tag for mark-and-sweep
 	char roots; // number of root users
-	struct gc_allocation_t *next; // separate chaining
+	struct gc_allocation *next; // separate chaining
+	struct gc_allocation *cut;
 } gc_allocation_t;
 
 typedef struct gc_allocation_map {
@@ -79,6 +81,7 @@ static gc_allocation_t *gc_allocation_new(void *ptr, size_t size) {
 	a->tag = GC_TAG_NONE;
 	a->roots = 0;
 	a->next = NULL;
+	a->cut = NULL;
 	return a;
 }
 
@@ -309,6 +312,39 @@ void _gc_unroot(void *ptr) {
 	}
 }
 
+static inline uint64_t pad(int di, int n) {
+	return (n - (di % n)) % n;
+}
+
+// Cut out a leaf out of an existing allocation
+void *_gc_cut(void *ptr, size_t pos, size_t size) {
+	size += pad(size, 8);
+
+	// Start
+	gc_allocation_t *start = gc_allocation_map_get(gc->allocs, ptr);
+	while (start->cut) {
+		start = start->cut;
+	}
+	size_t start_size = start->size;
+	pos -= start->ptr - ptr;
+	start->size = pos;
+
+	// Middle
+	gc_allocation_t *middle = gc_allocation_new(start->ptr + pos, size);
+	middle->tag |= GC_TAG_CUT;
+	middle->tag |= GC_TAG_LEAF;
+	start->cut = middle;
+	gc_allocation_map_put(gc->allocs, middle);
+
+	// End
+	gc_allocation_t *end = gc_allocation_new(start->ptr + pos + size, start_size - size - pos);
+	end->tag |= GC_TAG_CUT;
+	middle->cut = end;
+	gc_allocation_map_put(gc->allocs, end);
+
+	return middle->ptr;
+}
+
 static void gc_mark_alloc(void *ptr) {
 	gc_allocation_t *alloc = gc_allocation_map_get(gc->allocs, ptr);
 	/* Mark if alloc exists and is not tagged already, otherwise skip */
@@ -317,6 +353,7 @@ static void gc_mark_alloc(void *ptr) {
 		if (!(alloc->tag & GC_TAG_LEAF)) { // Skip contents
 			/* Iterate over allocation contents and mark them as well */
 			int size = alloc->array_length ? (*alloc->array_length) * PTRSIZE : alloc->size;
+
 			for (char *p = (char *)alloc->ptr; p <= (char *)alloc->ptr + size - PTRSIZE; ++p) {
 				gc_mark_alloc(*(void **)p);
 			}
@@ -370,13 +407,22 @@ static size_t gc_sweep() {
 				chunk->tag &= ~GC_TAG_MARK;
 				chunk = chunk->next;
 			}
+			else if (chunk->tag & GC_TAG_CUT) {
+				chunk = chunk->next;
+			}
 			else {
 				/* no reference to this chunk, hence delete it */
 				total += chunk->size;
 				free(chunk->ptr);
 				/* and remove it from the bookkeeping */
 				next = chunk->next;
+				gc_allocation_t *cut = chunk->cut;
 				gc_allocation_map_remove(gc->allocs, chunk->ptr, false);
+				while (cut) {
+					gc_allocation_t *next = cut->cut;
+					gc_allocation_map_remove(gc->allocs, cut->ptr, false);
+					cut = next;
+				}
 				chunk = next;
 			}
 		}
diff --git a/sources/libs/gc.h b/sources/libs/gc.h
index cbcd42e2..b95b1ff3 100644
--- a/sources/libs/gc.h
+++ b/sources/libs/gc.h
@@ -16,5 +16,6 @@ void _gc_array(void *ptr, int *length);
 void _gc_leaf(void *ptr);
 void _gc_root(void *ptr);
 void _gc_unroot(void *ptr);
+void *_gc_cut(void *ptr, size_t pos, size_t size);
 void *_gc_realloc(void *ptr, size_t size);
 void _gc_free(void *ptr);