Implement `hash' for structs.

* libguile/hash.c (scm_hasher): Call `scm_i_struct_hash' upon
  `scm_tcs_struct'.
* libguile/struct.c (scm_i_struct_hash): New function.
* libguile/struct.h (scm_i_struct_hash): New declaration.

* test-suite/tests/structs.test ("hash"): New test prefix.

libguile/hash.c

@@ -1,5 +1,6 @@
-/*	Copyright (C) 1995,1996,1997, 2000, 2001, 2003, 2004, 2006, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
- * 
+/* Copyright (C) 1995, 1996, 1997, 2000, 2001, 2003, 2004, 2006, 2008,
+ *   2009, 2010, 2011, 2012 Free Software Foundation, Inc.
+ *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
  * as published by the Free Software Foundation; either version 3 of
@@ -223,6 +224,8 @@ scm_hasher(SCM obj, unsigned long n, size_t d)
 	significant_bits = (scm_t_uintptr) SCM_POINTER_VALUE (obj) >> 4UL;
 	return (size_t) significant_bits  % n;
       }
+    case scm_tcs_struct:
+      return scm_i_struct_hash (obj, n, d);
     case scm_tc7_wvect:
     case scm_tc7_vector:
       {

libguile/struct.c

@@ -922,6 +922,55 @@ scm_struct_ihashq (SCM obj, unsigned long n, void *closure)
   return SCM_UNPACK (obj) % n;
 }
 
+/* Return the hash of struct OBJ, modulo N.  Traverse OBJ's fields to
+   compute the result, unless DEPTH is zero.  */
+unsigned long
+scm_i_struct_hash (SCM obj, unsigned long n, size_t depth)
+#define FUNC_NAME "hash"
+{
+  SCM layout;
+  scm_t_bits *data;
+  size_t struct_size, field_num;
+  unsigned long hash;
+
+  SCM_VALIDATE_STRUCT (1, obj);
+
+  layout = SCM_STRUCT_LAYOUT (obj);
+  struct_size = scm_i_symbol_length (layout) / 2;
+  data = SCM_STRUCT_DATA (obj);
+
+  hash = SCM_UNPACK (SCM_STRUCT_VTABLE (obj)) % n;
+  if (depth > 0)
+    for (field_num = 0; field_num < struct_size; field_num++)
+      {
+	int protection;
+
+	protection = scm_i_symbol_ref (layout, field_num * 2 + 1);
+	if (protection != 'h' && protection != 'o')
+	  {
+	    int type;
+	    type = scm_i_symbol_ref (layout, field_num * 2);
+	    switch (type)
+	      {
+	      case 'p':
+		hash ^= scm_hasher (SCM_PACK (data[field_num]), n,
+				    depth / 2);
+		break;
+	      case 'u':
+		hash ^= data[field_num] % n;
+		break;
+	      default:
+		/* Ignore 's' fields.  */;
+	      }
+	  }
+      }
+
+  /* FIXME: Tail elements should be taken into account.  */
+
+  return hash % n;
+}
+#undef FUNC_NAME
+
 SCM_DEFINE (scm_struct_vtable_name, "struct-vtable-name", 1, 0, 0, 
             (SCM vtable),
 	    "Return the name of the vtable @var{vtable}.")

libguile/struct.h

@@ -193,6 +193,8 @@ SCM_API void scm_print_struct (SCM exp, SCM port, scm_print_state *);
 
 SCM_INTERNAL SCM scm_i_struct_equalp (SCM s1, SCM s2);
 SCM_INTERNAL unsigned long scm_struct_ihashq (SCM, unsigned long, void *);
+SCM_INTERNAL unsigned long scm_i_struct_hash (SCM s, unsigned long n,
+					      size_t depth);
 SCM_INTERNAL SCM scm_i_alloc_struct (scm_t_bits *vtable_data, int n_words);
 SCM_INTERNAL void scm_i_struct_inherit_vtable_magic (SCM vtable, SCM obj);
 SCM_INTERNAL void scm_init_struct (void);

test-suite/tests/structs.test

@@ -126,7 +126,49 @@
      (not (or (equal? (make-ball red "Bob") (make-ball green "Bob"))
 	      (equal? (make-ball red "Bob") (make-ball red "Bill"))))))
 
+
+(with-test-prefix "hash"
 
+  (pass-if "simple structs"
+    (let* ((v  (make-vtable "pr"))
+           (s1 (make-struct v 0 "hello"))
+           (s2 (make-struct v 0 "hello")))
+      (= (hash s1 7777) (hash s2 7777))))
+
+  (pass-if "different structs"
+    (let* ((v  (make-vtable "pr"))
+           (s1 (make-struct v 0 "hello"))
+           (s2 (make-struct v 0 "world")))
+      (or (not (= (hash s1 7777) (hash s2 7777)))
+          (throw 'unresolved))))
+
+  (pass-if "different struct types"
+    (let* ((v1 (make-vtable "pr"))
+           (v2 (make-vtable "pr"))
+           (s1 (make-struct v1 0 "hello"))
+           (s2 (make-struct v2 0 "hello")))
+      (or (not (= (hash s1 7777) (hash s2 7777)))
+          (throw 'unresolved))))
+
+  (pass-if "more complex structs"
+    (let ((s1 (make-ball red (string-copy "Bob")))
+          (s2 (make-ball red (string-copy "Bob"))))
+      (= (hash s1 7777) (hash s2 7777))))
+
+  (pass-if "struct with weird fields"
+    (let* ((v  (make-vtable "prurph"))
+           (s1 (make-struct v 0 "hello" 123 "invisible-secret1"))
+           (s2 (make-struct v 0 "hello" 123 "invisible-secret2")))
+      (= (hash s1 7777) (hash s2 7777))))
+
+  (pass-if "cyclic structs"
+    (let* ((v (make-vtable "pw"))
+           (a (make-struct v 0 #f))
+           (b (make-struct v 0 a)))
+      (struct-set! a 0 b)
+      (and (hash a 7777) (hash b 7777) #t))))
+
+
 ;;
 ;; make-struct
 ;;