154 lines
4.4 KiB
C
Executable File
154 lines
4.4 KiB
C
Executable File
/*************************************************************************
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* *
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* YAP Prolog %W% %G% *
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* Yap Prolog was developed at NCCUP - Universidade do Porto *
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* *
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* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
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* *
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**************************************************************************
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* *
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* File: YapHandles.h *
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* mods: *
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* comments: term handles for YAP: basic ops *
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* version: $Id: Yap.h,v 1.38 2008-06-18 10:02:27 vsc Exp $ *
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*************************************************************************/
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#ifndef YAP_HANDLES_H
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#define YAP_HANDLES_H 1
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#include "Regs.h"
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/**
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@group term_t_slots
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Also known as term handles, slots are offsets to entries in the local stack. YAP never compresses the local stack, so slots are respected by the garbage collector,
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hence providing a way to access terms without being exposed to stack shifts or garbage-collection.
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Space is released when the function terminataes. Thus, slots will be automatically released at the end
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of a function. Hence, slots should always be used as local variables.
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Slots are organized as follows:
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---- Offset of next pointer in chain (tagged as an handle_t)
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---- Number of entries (tagged as handle_t), in the example TAG(INT,4)
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Entry
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Entry
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Entry
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Entry
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---- Number of entries (tagged as handle_t), in the example TAG(INT,4)
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Slots are not known to the yaam. Instead, A new set of slots is created when the emulator calls user C-code.
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(see YAP_Execute* functions). They are also created:
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- by SWI's PL_foreign_frame() function,
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- by the YAP_RunGoal() routines and friends, when they exit successfully. Notice that all handles created by c-goals within
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a `Goal` execution should not be used afterwards.
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This section lists the main internal functions for slot management. These functions are then exported through corresponding FLI C-functions
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*************************************************************************************************/
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/// @brief start a new set of slots, linking them to the last active slots (who may, or not, be active).
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static inline handle_t
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Yap_StartSlots( USES_REGS1 ) {
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handle_t CurSlot = LOCAL_CurSlot;
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// if (CurSlot == LCL0-(ASP+(IntOfTerm(ASP[0])+2)))
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// return CurSlot;
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/* new slot */
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*--ASP = MkIntegerTerm(CurSlot);
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LOCAL_CurSlot = LCL0-ASP;
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*--ASP = MkIntTerm(0);
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*--ASP = MkIntTerm(0);
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return CurSlot;
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}
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/// @brief reset slots to a well-known position in the stack
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static inline void
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Yap_CloseSlots( handle_t slot USES_REGS ) {
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LOCAL_CurSlot = slot;
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}
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/// @brief report the current position of the slots, assuming that they occupy the top of the stack.
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static inline handle_t
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Yap_CurrentSlot( USES_REGS1 ) {
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return IntOfTerm(ASP[0]);
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}
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/// @brief read from a slot.
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static inline Term
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Yap_GetFromSlot(handle_t slot USES_REGS)
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{
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return(Deref(LCL0[slot]));
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}
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/// @brief read from a slot. but does not try to dereference the slot.
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static inline Term
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Yap_GetDerefedFromSlot(handle_t slot USES_REGS)
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{
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return LCL0[slot];
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}
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/// @brief read the object in a slot. but do not try to dereference the slot.
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static inline Term
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Yap_GetPtrFromSlot(handle_t slot USES_REGS)
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{
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return(LCL0[slot]);
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}
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/// @brief get the memory address of a slot
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static inline Term *
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Yap_AddressFromSlot(handle_t slot USES_REGS)
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{
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return(LCL0+slot);
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}
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/// @brief store term in a slot
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static inline void
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Yap_PutInSlot(handle_t slot, Term t USES_REGS)
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{
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LCL0[slot] = t;
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}
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/// @brief allocate n empty new slots
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static inline handle_t
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Yap_NewSlots(int n USES_REGS)
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{
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handle_t old_slots = IntOfTerm(ASP[0]), oldn = n;
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while (n > 0) {
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RESET_VARIABLE(ASP);
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ASP--;
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n--;
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}
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ASP[old_slots+oldn+1] = ASP[0] = MkIntTerm(old_slots+oldn);
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return((ASP+1)-LCL0);
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}
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/// @brief create a new slot with term t
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static inline Int
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Yap_InitSlot(Term t USES_REGS)
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{
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handle_t old_slots = IntOfTerm(ASP[0]);
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*ASP = t;
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ASP--;
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ASP[old_slots+2] = ASP[0] = MkIntTerm(old_slots+1);
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return((ASP+1)-LCL0);
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}
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/// @brief Succeeds if it is to recover the space allocated for $n$ contiguos slots starting at topSlot.
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static inline int
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Yap_RecoverSlots(int n, handle_t topSlot USES_REGS)
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{
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handle_t old_slots = IntOfTerm(ASP[0]);
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if (old_slots < n) {
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return FALSE;
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}
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if (ASP+1 != LCL0+topSlot)
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return FALSE;
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ASP += n;
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ASP[old_slots+(n-1)] = ASP[0] = MkIntTerm(old_slots-n);
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return TRUE;
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}
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#endif
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