1 files changed, 44 insertions, 0 deletions
diff --git a/lib/alloc/static_scratch_alloc.c b/lib/alloc/static_scratch_alloc.c
new file mode 100644
index 0000000..2489b98
--- /dev/null
+++ b/lib/alloc/static_scratch_alloc.c
@@ -0,0 +1,44 @@
+#include <errno.h>
+#include <setjmp.h>
+#include <stdckdint.h>
+#include <stdint.h>
+
+#include "alloc.h"
+#include "errors.h"
+
+[[noreturn]] static void oom(jmp_buf *env);
+
+void *
+static_scratch_alloc(allocator_t mem, alloc_mode_t mode, void *,
+					 ptrdiff_t, ptrdiff_t newnmemb, ptrdiff_t elemsz,
+					 ptrdiff_t align) 
+{
+	st_buf_t *ctx = mem.ctx;
+	
+	switch (mode) {
+	case ALLOC_NEW:
+	case ALLOC_RESIZE:
+		ptrdiff_t pad, avail, total;
+		if (ckd_mul(&total, newnmemb, elemsz))
+			oom(mem.err);
+		pad = -(uintptr_t)ctx->buf & (align - 1);
+		avail = ctx->len - pad;
+		if (avail < 0 || total > avail)
+			oom(mem.err);
+		return (char *)ctx->buf + pad;
+	case ALLOC_FREE:
+	case ALLOC_FREEALL:
+		return nullptr;
+	default:
+		unreachable();
+	}
+}
+
+void
+oom(jmp_buf *env)
+{
+	errno = ENOMEM;
+	if (env != nullptr)
+		longjmp(*env, 1);
+	err("static_scratch_alloc:");
+}