Add support for big-endian architectures

doc/impl.md

@@ -148,8 +148,6 @@ to keep the implementation terse, but should not hinder normal usage:
 * The garbage collector recurses on the `CAR` of objects thus deeply nested
   `CAR`s may overflow the C stack — an object's `CDR` is looped on and will not
   overflow the stack
-* The storage of an object's type and GC mark assumes a little-endian system and
-  will not work correctly on systems of other endianness
 * Proper tailcalls are not implemented — `while` can be used for iterating over
   lists
 * Strings are null-terminated and therefor not binary safe

src/fe.c

@@ -26,19 +26,20 @@
 #define unused(x)     ( (void) (x) )
 #define car(x)        ( (x)->car.o )
 #define cdr(x)        ( (x)->cdr.o )
-#define tag(x)        ( (x)->car.c )
+#define tag(x)        ( (x)->car.s[!endian.c * STRBUFSIZE] )
 #define isnil(x)      ( (x) == &nil )
 #define type(x)       ( tag(x) & 0x1 ? tag(x) >> 2 : FE_TPAIR )
 #define settype(x,t)  ( tag(x) = (t) << 2 | 1 )
 #define number(x)     ( (x)->cdr.n )
-#define prim(x)       ( (x)->cdr.c )
+#define prim(x)       ( (x)->cdr.s[!endian.c * STRBUFSIZE] )
 #define cfunc(x)      ( (x)->cdr.f )
-#define strbuf(x)     ( &(x)->car.c + 1 )
+#define strbuf(x)     ( (x)->car.s + endian.c )
 
 #define STRBUFSIZE    ( (int) sizeof(fe_Object*) - 1 )
 #define GCMARKBIT     ( 0x2 )
 #define GCSTACKSIZE   ( 256 )
 
+static const union { size_t u; char c; } endian = { 0x1 };
 
 enum {
  P_LET, P_SET, P_IF, P_FN, P_MAC, P_WHILE, P_QUOTE, P_AND, P_OR, P_DO, P_CONS,
@@ -57,7 +58,7 @@ static const char *typenames[] = {
   "func", "macro", "prim", "cfunc", "ptr"
 };
 
-typedef union { fe_Object *o; fe_CFunc f; fe_Number n; char c; } Value;
+typedef union { fe_Object *o; fe_CFunc f; fe_Number n; char s[STRBUFSIZE + 1]; } Value;
 
 struct fe_Object { Value car, cdr; };