1 files changed, 275 insertions, 0 deletions
diff --git a/memory/memory.c b/memory/memory.c
new file mode 100644
index 0000000..0c998c7
--- /dev/null
+++ b/memory/memory.c
@@ -0,0 +1,275 @@
+#include "memory.h"
+
+size_t clamp_top(size_t size, size_t top)
+{
+  return size > top ? top : size;
+}
+
+uintptr_t mem_clamp_top(uintptr_t mem, uintptr_t top)
+{
+  return mem > top ? top : mem;
+}
+
+b8 is_power_of_two(uintptr_t x) {
+  return (x & (x-1)) == 0;
+}
+
+uintptr_t align_forward(uintptr_t ptr, size_t alignment) {
+  uintptr_t p, a, modulo;
+
+  assert(is_power_of_two(alignment));
+
+  p = ptr;
+  a = (uintptr_t)alignment;
+  modulo = p & (a-1);
+
+  if (modulo != 0) {
+    p += (a - modulo);
+  }
+
+  return p;
+}
+
+//===========================================================================================
+// ---------------------------------- Arena -------------------------------------------------
+//===========================================================================================
+
+/*
+  A cases where arena allocation WILL fail:
+  | size = size_t + ${some_number_that_comes_up_higher_than_offset}
+  
+  This is because there is no check being made 
+*/
+void arena_init(struct Arena* a, unsigned char* backing_store, size_t capacity) {
+  a->buffer = backing_store;
+  a->curr_offset = 0;
+  a->prev_offset = 0;
+  a->capacity = capacity;
+}
+
+void* arena_alloc_aligned(struct Arena* a, size_t size, size_t alignment) {
+  void* ptr = NULL;
+
+  assert(is_power_of_two(alignment));
+
+  uintptr_t curr_ptr = (uintptr_t)a->buffer + a->curr_offset;
+  uintptr_t offset = align_forward(curr_ptr, alignment);
+  offset = offset - (uintptr_t)a->buffer;
+
+  if (size <= a->capacity - offset)
+  {
+    ptr = &a->buffer[offset];
+    a->prev_offset = a->curr_offset;
+    a->curr_offset = offset + size;
+    memset(ptr, 0, size);
+  }
+
+  return ptr;
+}
+
+void* arena_alloc(struct Arena* a, size_t size) {
+  return arena_alloc_aligned(a, size, DEFAULT_ALIGNMENT);
+}
+
+void* arena_resize_aligned(struct Arena* a, void* old_memory, size_t old_size,
+                                    size_t new_size, size_t alignment) 
+{
+  unsigned char* old = (unsigned char*)old_memory;
+  void* ptr = NULL;
+
+  assert(is_power_of_two(alignment));
+
+  if (old >= a->buffer && old < a->buffer + a->capacity)
+  {
+    if (a->buffer + a->prev_offset == old)
+    {
+      // extend_last_element
+      if (new_size > old_size)
+      {
+        size_t size_increase = new_size - old_size;
+        if (size_increase > (a->capacity - a->curr_offset))
+        {
+          new_size = old_size;
+          size_increase = 0;
+        }
+        memset(&a->buffer[a->curr_offset], 0, size_increase);
+      }
+      a->curr_offset = a->prev_offset + new_size;
+      ptr = old_memory;
+    }
+    else
+    {
+      ptr = arena_alloc_aligned(a, new_size, alignment);
+      if (ptr != NULL)
+      {
+        size_t copy_size = old_size < new_size ? old_size : new_size;
+        memmove(ptr, old_memory, copy_size);
+      }
+    }
+  }
+  
+  return ptr;
+}
+
+void* arena_resize(struct Arena* a, void* old_mem, size_t old_size,
+                            size_t new_size) {
+  return arena_resize_aligned(a, old_mem, old_size, new_size, DEFAULT_ALIGNMENT);
+}
+
+void arena_clear(struct Arena *a) {
+  a->curr_offset = 0;
+  a->prev_offset = 0;
+}
+
+//===========================================================================================
+// ---------------------------------- STACK -------------------------------------------------
+//===========================================================================================
+
+void stack_init(struct stack* s, void *backing_store, size_t capacity) 
+{
+  s->buffer = (unsigned char*)backing_store;
+  s->prev_offset = 0;
+  s->curr_offset = 0;
+  s->capacity = capacity;
+}
+
+uintptr_t fast_modulo(uintptr_t p, uintptr_t a)
+{
+  return (p & (a-1));
+}
+
+size_t calc_padding_with_header(uintptr_t ptr, uintptr_t alignment, size_t hdr_sz)
+{
+  uintptr_t p, a, modulo, padding, space_needed;
+
+  assert(is_power_of_two(alignment));
+
+  padding = space_needed = 0;
+
+  p = ptr;
+  a = alignment;
+  modulo = fast_modulo(p, a);
+
+  if (modulo != 0) {
+    padding = a - modulo;
+  }
+
+  space_needed = (uintptr_t)hdr_sz;
+  if (padding < space_needed)
+  {
+    space_needed -= padding;
+    if (fast_modulo(space_needed, a) != 0)
+    {
+      padding = padding + space_needed + a;
+    }
+    else
+    {
+      padding = padding + space_needed;
+    }
+  }
+
+  return (size_t)padding;
+}
+
+struct ResVoid stack_alloc_aligned(struct stack* s, size_t size, size_t alignment) 
+{
+  uintptr_t curr_addr, next_addr;
+  size_t padding;
+  struct stack_hdr *header;
+
+  assert(is_power_of_two(alignment));
+  if (alignment > 128) {
+    alignment = 128;
+  }
+
+  struct ResVoid result = {0};
+
+  curr_addr = (uintptr_t)s->buffer + (uintptr_t)s->curr_offset;
+  padding = calc_padding_with_header(curr_addr, (uintptr_t)alignment, sizeof(struct stack_hdr));
+
+  if (size > s->capacity - (s->curr_offset + padding))
+  {
+    result.status = MEM_FULL;
+    return result;
+  }
+
+  next_addr = curr_addr + (uintptr_t)padding;
+  header = (struct stack_hdr*)(next_addr - sizeof(struct stack_hdr));
+  header->prev_offset = s->prev_offset;
+  header->padding = padding;
+
+  s->prev_offset = s->curr_offset + padding;
+  s->curr_offset = s->prev_offset + size;
+
+  result.memory = memset((void *)next_addr, 0, size);
+  result.bytes_count = size;
+
+  return result;
+}
+
+struct ResVoid stack_alloc(struct stack* s, size_t size) 
+{
+  return stack_alloc_aligned(s, size, DEFAULT_ALIGNMENT);
+}
+
+enum MemStatus stack_free(struct stack* s)
+{
+  uintptr_t last_ele = (uintptr_t)s->buffer + (uintptr_t)s->prev_offset;
+  struct stack_hdr *header = (struct stack_hdr *)(last_ele - sizeof(struct stack_hdr));
+
+  uintptr_t prev_ele = (uintptr_t)s->buffer + (uintptr_t)header->prev_offset;
+  s->curr_offset = (size_t)((last_ele - (uintptr_t)header->padding) - (uintptr_t)s->buffer); 
+  s->prev_offset = (size_t)(prev_ele - (uintptr_t)s->buffer);
+  
+  return MEM_OK;
+}
+
+struct ResVoid stack_resize_aligned(struct stack* s, void* old_memory, size_t old_size,
+                                    size_t new_size, size_t alignment)
+{
+  struct ResVoid result = {0};
+
+  if (old_memory < s->buffer || old_memory > s->buffer + s->capacity) 
+  {
+    result.status = MEM_OUT_OF_BOUNDS;
+    return result;
+  }
+
+  // is_last_element()
+  if (s->buffer + s->prev_offset == old_memory)
+  {
+    if (new_size > old_size)
+    {
+      size_t size_difference = new_size - old_size;
+      if (size_difference > s->capacity - s->curr_offset)
+      {
+        result.status = MEM_FULL;
+        return result;
+      }
+
+      memset(&s->buffer[s->curr_offset], 0, size_difference);
+    }
+    s->curr_offset = s->prev_offset + new_size;
+
+    result.memory = old_memory;
+    return result;
+  }
+
+  result = stack_alloc_aligned(s, new_size, alignment);
+  size_t min_size = old_size < result.bytes_count ? old_size : result.bytes_count;
+  memmove(result.memory, old_memory, min_size);
+
+  return result;
+}
+
+struct ResVoid stack_resize(struct stack* s, void* old_memory, size_t old_size, size_t new_size)
+{
+  return stack_resize_aligned(s, old_memory, old_size, new_size, DEFAULT_ALIGNMENT);
+}
+
+void stack_clear(struct stack* s)
+{
+  s->prev_offset = 0;
+  s->curr_offset = 0;
+}
+