runtime/gc/objptr.c

   1 /* Copyright (C) 2005-2007 Henry Cejtin, Matthew Fluet, Suresh
   2  *    Jagannathan, and Stephen Weeks.
   3  *
   4  * MLton is released under a BSD-style license.
   5  * See the file MLton-LICENSE for details.
   6  */
   7
   8 /* isObjptr returns true if p looks like an object pointer. */
   9 bool isObjptr (objptr p) {
  10   unsigned int shift = GC_MODEL_MINALIGN_SHIFT - GC_MODEL_OBJPTR_SHIFT;
  11   objptr mask = ~((~((objptr)0)) << shift);
  12   return (0 == (p & mask));
  13 }
  14
  15 pointer objptrToPointer (objptr O, pointer B) {
  16   uintptr_t O_ = (uintptr_t)O;
  17   uintptr_t B_;
  18   unsigned int S_ = GC_MODEL_OBJPTR_SHIFT;
  19   uintptr_t P_;
  20   pointer P;
  21
  22   if (GC_MODEL_OBJPTR_BASE) {
  23     B_ = (uintptr_t)B;
  24   } else {
  25     B_ = 0;
  26   }
  27
  28   P_ = ((O_ << S_) + B_);
  29   P = (pointer)P_;
  30   if (DEBUG_OBJPTR)
  31     fprintf (stderr, "objptrToPointer ("FMTOBJPTR") = "FMTPTR"\n", O, (uintptr_t)P);
  32
  33   return P;
  34 }
  35
  36 objptr pointerToObjptr (pointer P, pointer B) {
  37   uintptr_t P_ = (uintptr_t)P;
  38   uintptr_t B_;
  39   unsigned int S_ = GC_MODEL_OBJPTR_SHIFT;
  40   uintptr_t O_;
  41   objptr O;
  42
  43   if (GC_MODEL_OBJPTR_BASE) {
  44     B_ = (uintptr_t)B;
  45   } else {
  46     B_ = 0;
  47   }
  48
  49   O_ = ((P_ - B_) >> S_);
  50   O = (objptr)O_;
  51   if (DEBUG_OBJPTR)
  52     fprintf (stderr, "pointerToObjptr ("FMTPTR") = "FMTOBJPTR"\n", (uintptr_t)P, O);
  53
  54   return O;
  55 }
  56
  57 /*
  58  * Note that by indirectly fetching and storing object pointers, the
  59  * following functions admit implementations that behave according to
  60  * model characteristics determined at runtime.  Hence, by making
  61  * exclusive use of these functions (and adding a GC_state->model
  62  * field set by the compiled program), we may be able to implement the
  63  * runtime in a manner which is agnostic to the actual objptr
  64  * representation.
  65  */
  66 pointer fetchObjptrToPointer (pointer OP, pointer B) {
  67   return objptrToPointer (*((objptr*)OP), B);
  68 }
  69 void storeObjptrFromPointer (pointer OP, pointer P, pointer B) {
  70   *((objptr*)OP) = pointerToObjptr (P, B);
  71 }