From 95856cb4f3279567339f78160b340735c3d53b19 Mon Sep 17 00:00:00 2001
From: Joshua Suskalo <joshua@iris.tv>
Date: Mon, 10 Jan 2022 13:31:27 -0600
Subject: [PATCH] Add with-c-layout function

---
 src/clj/coffi/layout.clj | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 src/clj/coffi/layout.clj

diff --git a/src/clj/coffi/layout.clj b/src/clj/coffi/layout.clj
new file mode 100644
index 0000000..d92e02d
--- /dev/null
+++ b/src/clj/coffi/layout.clj
@@ -0,0 +1,29 @@
+(ns coffi.layout
+  "Functions for adjusting the layout of structs."
+  (:require
+   [coffi.mem :as mem]))
+
+(defn with-c-layout
+  "Forces a struct specification to C layout rules.
+
+  This will add padding fields between fields to match C alignment
+  requirements."
+  [struct-spec]
+  (let [aligned-fields
+        (loop [offset 0
+               aligned-fields []
+               fields (nth struct-spec 1)]
+          (if (seq fields)
+            (let [[[_ type :as field] & fields] fields
+                  size (mem/size-of type)
+                  r (rem offset (mem/align-of type))]
+              (recur (+ offset r size)
+                     (cond-> aligned-fields
+                       (pos? r) (conj [:padding [::mem/padding r]])
+                       :always (conj field))
+                     fields))
+            (let [strongest-alignment (mem/align-of struct-spec)
+                  r (rem offset strongest-alignment)]
+              (cond-> aligned-fields
+                (pos? r) (conj [:padding [::mem/padding r]])))))]
+    (assoc struct-spec 1 aligned-fields)))