From: Kaz Wesley <kaz@lambdaverse.org>
Date: Sat, 10 Feb 2018 02:15:50 +0000 (-0800)
Subject: Endian-aware FIX32 layout.
X-Git-Url: https://jxself.org/git/?a=commitdiff_plain;h=56694525a0ce70e971de1f145c714a30ecce6742;hp=6329da4e468e5429ad2d56eb274edaac72704cab;p=muddle-interpreter.git

Endian-aware FIX32 layout.

Allows upcasting a FIX32 by reading it as if it were a FIX64.

Signed-off-by: Kaz Wesley <kaz@lambdaverse.org>
---

diff --git a/src/object.h b/src/object.h
index 54281f2..56f17b6 100644
--- a/src/object.h
+++ b/src/object.h
@@ -122,8 +122,17 @@ typedef union object object;
 
 typedef struct
 {
-  alignas (8) uint32_t _pad;
+  alignas (8)
+    // layout so that value can be upcast by reinterpreting as a fix64
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+  int32_t n;
+  uint32_t _pad;
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+  uint32_t _pad;
   int32_t n;
+#else
+#error Unusual endianness?
+#endif
 } fix32_val;
 typedef struct
 {
@@ -410,6 +419,13 @@ object *stack_push (vector_object * v);
 Checked downcasts.
 */
 
+static inline fix32_object *
+as_fix32 (object * o)
+{
+  assert (TYPEPRIM_EQ (o->type, TYPEPRIM_FIX32));
+  return &o->fix32;
+}
+
 static inline list_object *
 as_list (object * o)
 {