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examples/modules/allocators.sx

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+#import "std.sx";
+
+// --- Allocator protocol ---
+
+Allocator :: struct {
+    ctx: *void;
+    alloc: (*void, s64) -> *void;
+    free: (*void, *void) -> void;
+}
+
+// --- GPA: general purpose allocator (malloc/free wrapper) ---
+
+GPA :: struct {
+    alloc_count: s64;
+}
+
+gpa_alloc :: (ctx: *void, size: s64) -> *void {
+    gpa : *GPA = xx ctx;
+    gpa.alloc_count += 1;
+    malloc(size);
+}
+
+gpa_free :: (ctx: *void, ptr: *void) {
+    gpa : *GPA = xx ctx;
+    gpa.alloc_count -= 1;
+    free(ptr);
+}
+
+gpa_create :: (gpa: *GPA) -> Allocator {
+    ctx : *void = xx gpa;
+    Allocator.{ ctx = ctx, alloc = gpa_alloc, free = gpa_free };
+}
+
+// --- Arena: multi-chunk bump allocator (Zig-inspired) ---
+
+ArenaChunk :: struct {
+    next: *void;    // *ArenaChunk
+    cap: s64;       // total chunk size including this header
+}
+
+Arena :: struct {
+    first: *void;       // *ArenaChunk — head of list (newest first)
+    end_index: s64;     // bump position within current chunk's usable area
+    parent: Allocator;  // backing allocator
+}
+
+arena_add_chunk :: (a: *Arena, min_size: s64) {
+    first_i : s64 = xx a.first;
+    prev_cap := if first_i != 0 then { c : *ArenaChunk = xx a.first; c.cap; } else 0;
+    needed := min_size + 16 + 16;
+    len := (prev_cap + needed) * 3 / 2;
+    raw := a.parent.alloc(a.parent.ctx, len);
+    chunk : *ArenaChunk = xx raw;
+    chunk.next = a.first;
+    chunk.cap = len;
+    a.first = xx chunk;
+    a.end_index = 0;
+}
+
+arena_alloc :: (ctx: *void, size: s64) -> *void {
+    a : *Arena = xx ctx;
+    aligned := (size + 7) & (0 - 8);
+    first_i : s64 = xx a.first;
+    if first_i != 0 {
+        chunk : *ArenaChunk = xx a.first;
+        usable := chunk.cap - 16;
+        if a.end_index + aligned <= usable {
+            buf : [*]u8 = xx a.first;
+            ptr : *void = xx @buf[16 + a.end_index];
+            a.end_index = a.end_index + aligned;
+            return ptr;
+        }
+    }
+    arena_add_chunk(a, aligned);
+    buf : [*]u8 = xx a.first;
+    ptr : *void = xx @buf[16 + a.end_index];
+    a.end_index = a.end_index + aligned;
+    ptr;
+}
+
+arena_free :: (ctx: *void, ptr: *void) {
+}
+
+arena_create :: (a: *Arena, parent: Allocator, size: s64) -> Allocator {
+    a.first = null;
+    a.end_index = 0;
+    a.parent = parent;
+    arena_add_chunk(a, size);
+    ctx : *void = xx a;
+    Allocator.{ ctx = ctx, alloc = arena_alloc, free = arena_free };
+}
+
+arena_reset :: (a: *Arena) {
+    // Keep first chunk (newest/largest), free the rest
+    first_i : s64 = xx a.first;
+    if first_i != 0 {
+        chunk : *ArenaChunk = xx a.first;
+        it : s64 = xx chunk.next;
+        while it != 0 {
+            c : *ArenaChunk = xx it;
+            next_i : s64 = xx c.next;
+            a.parent.free(a.parent.ctx, xx c);
+            it = next_i;
+        }
+        chunk.next = null;
+    }
+    a.end_index = 0;
+}
+
+arena_deinit :: (a: *Arena) {
+    it : s64 = xx a.first;
+    while it != 0 {
+        c : *ArenaChunk = xx it;
+        next_i : s64 = xx c.next;
+        a.parent.free(a.parent.ctx, xx c);
+        it = next_i;
+    }
+    a.first = null;
+    a.end_index = 0;
+}
+
+// --- BufAlloc: bump allocator backed by a user-provided slice ---
+
+BufAlloc :: struct {
+    buf: [*]u8;
+    len: s64;
+    pos: s64;
+}
+
+buf_alloc :: (ctx: *void, size: s64) -> *void {
+    b : *BufAlloc = xx ctx;
+    aligned := (size + 7) & (0 - 8);
+    if b.pos + aligned > b.len {
+        return null;
+    }
+    ptr : *void = xx @b.buf[b.pos];
+    b.pos = b.pos + aligned;
+    ptr;
+}
+
+buf_free :: (ctx: *void, ptr: *void) {
+}
+
+buf_create :: (b: *BufAlloc, buf: [*]u8, len: s64) -> Allocator {
+    b.buf = buf;
+    b.len = len;
+    b.pos = 0;
+    ctx : *void = xx b;
+    Allocator.{ ctx = ctx, alloc = buf_alloc, free = buf_free };
+}
+
+buf_reset :: (b: *BufAlloc) {
+    b.pos = 0;
+}