add realloc (and update c_allocator)

std/mem/mem.bro

@@ -3,6 +3,7 @@ c :: import "@ffi/c"
 Allocator :: struct {
 	context ?*mut anyopaque
 	alloc @func(context ?*mut anyopaque, size usize, alignment usize) ?*mut u8
+	realloc @func(context ?*mut anyopaque, memory ?*mut u8, old_size usize, new_size usize, alignment usize) ?*mut u8
 	free @func(context ?*mut anyopaque, memory ?*mut u8, size usize, alignment usize) void
 }
 
@@ -43,6 +44,39 @@ _c_alloc func(_ ?*mut anyopaque, size usize, alignment usize) ?*mut u8 {
 	return ptr_cast(u8, memory[0])
 }
 
+_c_realloc func(_ ?*mut anyopaque, memory ?*mut u8, old_size usize, new_size usize, alignment usize) ?*mut u8 {
+	if _power_of_two(alignment) == false {
+		return none
+	}
+
+	if new_size == 0 {
+		c.free(memory)
+		return none
+	}
+
+	if memory |old_memory| {
+		if alignment <= _malloc_alignment {
+			return ptr_cast(u8, c.realloc(old_memory, c_ulong(new_size)))
+		}
+
+		new_memory ?*mut u8 = _c_alloc(none, new_size, alignment)
+		if new_memory |new_bytes| {
+			copy_size usize = old_size
+			if new_size < copy_size {
+				copy_size = new_size
+			}
+			i usize = 0
+			while i < copy_size : i += 1 {
+				new_bytes[i] = old_memory[i]
+			}
+			c.free(old_memory)
+		}
+		return new_memory
+	}
+
+	return _c_alloc(none, new_size, alignment)
+}
+
 _c_free func(_ ?*mut anyopaque, memory ?*mut u8, _ usize, _ usize) void {
 	c.free(memory)
 }
@@ -50,6 +84,7 @@ _c_free func(_ ?*mut anyopaque, memory ?*mut u8, _ usize, _ usize) void {
 c_allocator Allocator :: Allocator {
 	context = none,
 	alloc = _c_alloc,
+	realloc = _c_realloc,
 	free = _c_free,
 }
 
@@ -57,6 +92,10 @@ alloc func(allocator Allocator, size usize, alignment usize) ?*mut u8 {
 	return allocator.alloc(allocator.context, size, alignment)
 }
 
+realloc func(allocator Allocator, memory ?*mut u8, old_size usize, new_size usize, alignment usize) ?*mut u8 {
+	return allocator.realloc(allocator.context, memory, old_size, new_size, alignment)
+}
+
 free func(allocator Allocator, memory ?*mut u8, size usize, alignment usize) void {
 	allocator.free(allocator.context, memory, size, alignment)
 }