bytecode.c

/* Execution of byte code produced by bytecomp.el.
   Copyright (C) 1985, 1986, 1987, 1988, 1993, 2000, 2001, 2002, 2003, 2004,
                 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */

/*
hacked on by jwz@lucid.com 17-jun-91
  o  added a compile-time switch to turn on simple sanity checking;
  o  put back the obsolete byte-codes for error-detection;
  o  added a new instruction, unbind_all, which I will use for
     tail-recursion elimination;
  o  made temp_output_buffer_show be called with the right number
     of args;
  o  made the new bytecodes be called with args in the right order;
  o  added metering support.

by Hallvard:
  o  added relative jump instructions;
  o  all conditionals now only do QUIT if they jump.
 */

#include <config.h>
#include <setjmp.h>
#include "lisp.h"
#include "buffer.h"
#include "character.h"
#include "syntax.h"
#include "window.h"

#ifdef CHECK_FRAME_FONT
#include "frame.h"
#include "xterm.h"
#endif

/*
 * define BYTE_CODE_SAFE to enable some minor sanity checking (useful for
 * debugging the byte compiler...)
 *
 * define BYTE_CODE_METER to enable generation of a byte-op usage histogram.
 */
/* #define BYTE_CODE_SAFE */
/* #define BYTE_CODE_METER */


#ifdef BYTE_CODE_METER

Lisp_Object Vbyte_code_meter, Qbyte_code_meter;
int byte_metering_on;

#define METER_2(code1, code2) \
  XFASTINT (XVECTOR (XVECTOR (Vbyte_code_meter)->contents[(code1)]) \
	    ->contents[(code2)])

#define METER_1(code) METER_2 (0, (code))

#define METER_CODE(last_code, this_code)				\
{									\
  if (byte_metering_on)							\
    {									\
      if (METER_1 (this_code) < MOST_POSITIVE_FIXNUM)			\
        METER_1 (this_code)++;						\
      if (last_code							\
	  && METER_2 (last_code, this_code) < MOST_POSITIVE_FIXNUM)	\
        METER_2 (last_code, this_code)++;				\
    }									\
}

#else /* no BYTE_CODE_METER */

#define METER_CODE(last_code, this_code)

#endif /* no BYTE_CODE_METER */


Lisp_Object Qbytecode;

/*  Byte codes: */

#define Bvarref 010
#define Bvarset 020
#define Bvarbind 030
#define Bcall 040
#define Bunbind 050

#define Bnth 070
#define Bsymbolp 071
#define Bconsp 072
#define Bstringp 073
#define Blistp 074
#define Beq 075
#define Bmemq 076
#define Bnot 077
#define Bcar 0100
#define Bcdr 0101
#define Bcons 0102
#define Blist1 0103
#define Blist2 0104
#define Blist3 0105
#define Blist4 0106
#define Blength 0107
#define Baref 0110
#define Baset 0111
#define Bsymbol_value 0112
#define Bsymbol_function 0113
#define Bset 0114
#define Bfset 0115
#define Bget 0116
#define Bsubstring 0117
#define Bconcat2 0120
#define Bconcat3 0121
#define Bconcat4 0122
#define Bsub1 0123
#define Badd1 0124
#define Beqlsign 0125
#define Bgtr 0126
#define Blss 0127
#define Bleq 0130
#define Bgeq 0131
#define Bdiff 0132
#define Bnegate 0133
#define Bplus 0134
#define Bmax 0135
#define Bmin 0136
#define Bmult 0137

#define Bpoint 0140
/* Was Bmark in v17.  */
#define Bsave_current_buffer 0141
#define Bgoto_char 0142
#define Binsert 0143
#define Bpoint_max 0144
#define Bpoint_min 0145
#define Bchar_after 0146
#define Bfollowing_char 0147
#define Bpreceding_char 0150
#define Bcurrent_column 0151
#define Bindent_to 0152
#define Bscan_buffer 0153 /* No longer generated as of v18 */
#define Beolp 0154
#define Beobp 0155
#define Bbolp 0156
#define Bbobp 0157
#define Bcurrent_buffer 0160
#define Bset_buffer 0161
#define Bsave_current_buffer_1 0162 /* Replacing Bsave_current_buffer.  */
#define Bread_char 0162 /* No longer generated as of v19 */
#define Bset_mark 0163 /* this loser is no longer generated as of v18 */
#define Binteractive_p 0164 /* Needed since interactive-p takes unevalled args */

#define Bforward_char 0165
#define Bforward_word 0166
#define Bskip_chars_forward 0167
#define Bskip_chars_backward 0170
#define Bforward_line 0171
#define Bchar_syntax 0172
#define Bbuffer_substring 0173
#define Bdelete_region 0174
#define Bnarrow_to_region 0175
#define Bwiden 0176
#define Bend_of_line 0177

#define Bconstant2 0201
#define Bgoto 0202
#define Bgotoifnil 0203
#define Bgotoifnonnil 0204
#define Bgotoifnilelsepop 0205
#define Bgotoifnonnilelsepop 0206
#define Breturn 0207
#define Bdiscard 0210
#define Bdup 0211

#define Bsave_excursion 0212
#define Bsave_window_excursion 0213
#define Bsave_restriction 0214
#define Bcatch 0215

#define Bunwind_protect 0216
#define Bcondition_case 0217
#define Btemp_output_buffer_setup 0220
#define Btemp_output_buffer_show 0221

#define Bunbind_all 0222

#define Bset_marker 0223
#define Bmatch_beginning 0224
#define Bmatch_end 0225
#define Bupcase 0226
#define Bdowncase 0227

#define Bstringeqlsign 0230
#define Bstringlss 0231
#define Bequal 0232
#define Bnthcdr 0233
#define Belt 0234
#define Bmember 0235
#define Bassq 0236
#define Bnreverse 0237
#define Bsetcar 0240
#define Bsetcdr 0241
#define Bcar_safe 0242
#define Bcdr_safe 0243
#define Bnconc 0244
#define Bquo 0245
#define Brem 0246
#define Bnumberp 0247
#define Bintegerp 0250

#define BRgoto 0252
#define BRgotoifnil 0253
#define BRgotoifnonnil 0254
#define BRgotoifnilelsepop 0255
#define BRgotoifnonnilelsepop 0256

#define BlistN 0257
#define BconcatN 0260
#define BinsertN 0261

#define Bconstant 0300
#define CONSTANTLIM 0100


/* Structure describing a value stack used during byte-code execution
   in Fbyte_code.  */

struct byte_stack
{
  /* Program counter.  This points into the byte_string below
     and is relocated when that string is relocated.  */
  const unsigned char *pc;

  /* Top and bottom of stack.  The bottom points to an area of memory
     allocated with alloca in Fbyte_code.  */
  Lisp_Object *top, *bottom;

  /* The string containing the byte-code, and its current address.
     Storing this here protects it from GC because mark_byte_stack
     marks it.  */
  Lisp_Object byte_string;
  const unsigned char *byte_string_start;

  /* The vector of constants used during byte-code execution.  Storing
     this here protects it from GC because mark_byte_stack marks it.  */
  Lisp_Object constants;

  /* Next entry in byte_stack_list.  */
  struct byte_stack *next;
};

/* A list of currently active byte-code execution value stacks.
   Fbyte_code adds an entry to the head of this list before it starts
   processing byte-code, and it removed the entry again when it is
   done.  Signalling an error truncates the list analoguous to
   gcprolist.  */

struct byte_stack *byte_stack_list;


/* Mark objects on byte_stack_list.  Called during GC.  */

void
mark_byte_stack ()
{
  struct byte_stack *stack;
  Lisp_Object *obj;

  for (stack = byte_stack_list; stack; stack = stack->next)
    {
      /* If STACK->top is null here, this means there's an opcode in
	 Fbyte_code that wasn't expected to GC, but did.  To find out
	 which opcode this is, record the value of `stack', and walk
	 up the stack in a debugger, stopping in frames of Fbyte_code.
	 The culprit is found in the frame of Fbyte_code where the
	 address of its local variable `stack' is equal to the
	 recorded value of `stack' here.  */
      eassert (stack->top);

      for (obj = stack->bottom; obj <= stack->top; ++obj)
	mark_object (*obj);

      mark_object (stack->byte_string);
      mark_object (stack->constants);
    }
}


/* Unmark objects in the stacks on byte_stack_list.  Relocate program
   counters.  Called when GC has completed.  */

void
unmark_byte_stack ()
{
  struct byte_stack *stack;

  for (stack = byte_stack_list; stack; stack = stack->next)
    {
      if (stack->byte_string_start != SDATA (stack->byte_string))
	{
	  int offset = stack->pc - stack->byte_string_start;
	  stack->byte_string_start = SDATA (stack->byte_string);
	  stack->pc = stack->byte_string_start + offset;
	}
    }
}


/* Fetch the next byte from the bytecode stream */

#define FETCH *stack.pc++

/* Fetch two bytes from the bytecode stream and make a 16-bit number
   out of them */

#define FETCH2 (op = FETCH, op + (FETCH << 8))

/* Push x onto the execution stack.  This used to be #define PUSH(x)
   (*++stackp = (x)) This oddity is necessary because Alliant can't be
   bothered to compile the preincrement operator properly, as of 4/91.
   -JimB */

#define PUSH(x) (top++, *top = (x))

/* Pop a value off the execution stack.  */

#define POP (*top--)

/* Discard n values from the execution stack.  */

#define DISCARD(n) (top -= (n))

/* Get the value which is at the top of the execution stack, but don't
   pop it. */

#define TOP (*top)

/* Actions that must be performed before and after calling a function
   that might GC.  */

#define BEFORE_POTENTIAL_GC()	stack.top = top
#define AFTER_POTENTIAL_GC()	stack.top = NULL

/* Garbage collect if we have consed enough since the last time.
   We do this at every branch, to avoid loops that never GC.  */

#define MAYBE_GC()					\
  if (consing_since_gc > gc_cons_threshold		\
      && consing_since_gc > gc_relative_threshold)	\
    {							\
      BEFORE_POTENTIAL_GC ();				\
      Fgarbage_collect ();				\
      AFTER_POTENTIAL_GC ();				\
    }							\
  else

/* Check for jumping out of range.  */

#ifdef BYTE_CODE_SAFE

#define CHECK_RANGE(ARG) \
  if (ARG >= bytestr_length) abort ()

#else /* not BYTE_CODE_SAFE */

#define CHECK_RANGE(ARG)

#endif /* not BYTE_CODE_SAFE */

/* A version of the QUIT macro which makes sure that the stack top is
   set before signaling `quit'.  */

#define BYTE_CODE_QUIT					\
  do {							\
    if (!NILP (Vquit_flag) && NILP (Vinhibit_quit))	\
      {							\
        Lisp_Object flag = Vquit_flag;			\
	Vquit_flag = Qnil;				\
        BEFORE_POTENTIAL_GC ();				\
	if (EQ (Vthrow_on_input, flag))			\
	  Fthrow (Vthrow_on_input, Qt);			\
	Fsignal (Qquit, Qnil);				\
	AFTER_POTENTIAL_GC ();				\
      }							\
    ELSE_PENDING_SIGNALS				\
  } while (0)


DEFUN ("byte-code", Fbyte_code, Sbyte_code, 3, 3, 0,
       doc: /* Function used internally in byte-compiled code.
The first argument, BYTESTR, is a string of byte code;
the second, VECTOR, a vector of constants;
the third, MAXDEPTH, the maximum stack depth used in this function.
If the third argument is incorrect, Emacs may crash.  */)
     (bytestr, vector, maxdepth)
     Lisp_Object bytestr, vector, maxdepth;
{
  int count = SPECPDL_INDEX ();
#ifdef BYTE_CODE_METER
  int this_op = 0;
  int prev_op;
#endif
  int op;
  /* Lisp_Object v1, v2; */
  Lisp_Object *vectorp;
#ifdef BYTE_CODE_SAFE
  int const_length = XVECTOR (vector)->size;
  Lisp_Object *stacke;
#endif
  int bytestr_length;
  struct byte_stack stack;
  Lisp_Object *top;
  Lisp_Object result;

#if 0 /* CHECK_FRAME_FONT */
 {
   struct frame *f = SELECTED_FRAME ();
   if (FRAME_X_P (f)
       && FRAME_FONT (f)->direction != 0
       && FRAME_FONT (f)->direction != 1)
     abort ();
 }
#endif

  CHECK_STRING (bytestr);
  CHECK_VECTOR (vector);
  CHECK_NUMBER (maxdepth);

  if (STRING_MULTIBYTE (bytestr))
    /* BYTESTR must have been produced by Emacs 20.2 or the earlier
       because they produced a raw 8-bit string for byte-code and now
       such a byte-code string is loaded as multibyte while raw 8-bit
       characters converted to multibyte form.  Thus, now we must
       convert them back to the originally intended unibyte form.  */
    bytestr = Fstring_as_unibyte (bytestr);

  bytestr_length = SBYTES (bytestr);
  vectorp = XVECTOR (vector)->contents;

  stack.byte_string = bytestr;
  stack.pc = stack.byte_string_start = SDATA (bytestr);
  stack.constants = vector;
  stack.bottom = (Lisp_Object *) alloca (XFASTINT (maxdepth)
                                         * sizeof (Lisp_Object));
  top = stack.bottom - 1;
  stack.top = NULL;
  stack.next = byte_stack_list;
  byte_stack_list = &stack;

#ifdef BYTE_CODE_SAFE
  stacke = stack.bottom - 1 + XFASTINT (maxdepth);
#endif

  while (1)
    {
#ifdef BYTE_CODE_SAFE
      if (top > stacke)
	abort ();
      else if (top < stack.bottom - 1)
	abort ();
#endif

#ifdef BYTE_CODE_METER
      prev_op = this_op;
      this_op = op = FETCH;
      METER_CODE (prev_op, op);
#else
      op = FETCH;
#endif

      switch (op)
	{
	case Bvarref + 7:
	  op = FETCH2;
	  goto varref;

	case Bvarref:
	case Bvarref + 1:
	case Bvarref + 2:
	case Bvarref + 3:
	case Bvarref + 4:
	case Bvarref + 5:
	  op = op - Bvarref;
	  goto varref;

	/* This seems to be the most frequently executed byte-code
	   among the Bvarref's, so avoid a goto here.  */
	case Bvarref+6:
	  op = FETCH;
	varref:
	  {
	    Lisp_Object v1, v2;

	    v1 = vectorp[op];
	    if (SYMBOLP (v1))
	      {
		v2 = SYMBOL_VALUE (v1);
		if (MISCP (v2) || EQ (v2, Qunbound))
		  {
		    BEFORE_POTENTIAL_GC ();
		    v2 = Fsymbol_value (v1);
		    AFTER_POTENTIAL_GC ();
		  }
	      }
	    else
	      {
		BEFORE_POTENTIAL_GC ();
		v2 = Fsymbol_value (v1);
		AFTER_POTENTIAL_GC ();
	      }
	    PUSH (v2);
	    break;
	  }

	case Bgotoifnil:
	  {
	    Lisp_Object v1;
	    MAYBE_GC ();
	    op = FETCH2;
	    v1 = POP;
	    if (NILP (v1))
	      {
		BYTE_CODE_QUIT;
		CHECK_RANGE (op);
		stack.pc = stack.byte_string_start + op;
	      }
	    break;
	  }

	case Bcar:
	  {
	    Lisp_Object v1;
	    v1 = TOP;
	    TOP = CAR (v1);
	    break;
	  }

	case Beq:
	  {
	    Lisp_Object v1;
	    v1 = POP;
	    TOP = EQ (v1, TOP) ? Qt : Qnil;
	    break;
	  }

	case Bmemq:
	  {
	    Lisp_Object v1;
	    BEFORE_POTENTIAL_GC ();
	    v1 = POP;
	    TOP = Fmemq (TOP, v1);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Bcdr:
	  {
	    Lisp_Object v1;
	    v1 = TOP;
	    TOP = CDR (v1);
	    break;
	  }

	case Bvarset:
	case Bvarset+1:
	case Bvarset+2:
	case Bvarset+3:
	case Bvarset+4:
	case Bvarset+5:
	  op -= Bvarset;
	  goto varset;

	case Bvarset+7:
	  op = FETCH2;
	  goto varset;

	case Bvarset+6:
	  op = FETCH;
	varset:
	  {
	    Lisp_Object sym, val;

	    sym = vectorp[op];
	    val = TOP;

	    /* Inline the most common case.  */
	    if (SYMBOLP (sym)
		&& !EQ (val, Qunbound)
		&& !XSYMBOL (sym)->indirect_variable
		&& !SYMBOL_CONSTANT_P (sym)
		&& !MISCP (XSYMBOL (sym)->value))
	      XSYMBOL (sym)->value = val;
	    else
	      {
		BEFORE_POTENTIAL_GC ();
		set_internal (sym, val, current_buffer, 0);
		AFTER_POTENTIAL_GC ();
	      }
	  }
	  (void) POP;
	  break;

	case Bdup:
	  {
	    Lisp_Object v1;
	    v1 = TOP;
	    PUSH (v1);
	    break;
	  }

	/* ------------------ */

	case Bvarbind+6:
	  op = FETCH;
	  goto varbind;

	case Bvarbind+7:
	  op = FETCH2;
	  goto varbind;

	case Bvarbind:
	case Bvarbind+1:
	case Bvarbind+2:
	case Bvarbind+3:
	case Bvarbind+4:
	case Bvarbind+5:
	  op -= Bvarbind;
	varbind:
	  /* Specbind can signal and thus GC.  */
	  BEFORE_POTENTIAL_GC ();
	  specbind (vectorp[op], POP);
	  AFTER_POTENTIAL_GC ();
	  break;

	case Bcall+6:
	  op = FETCH;
	  goto docall;

	case Bcall+7:
	  op = FETCH2;
	  goto docall;

	case Bcall:
	case Bcall+1:
	case Bcall+2:
	case Bcall+3:
	case Bcall+4:
	case Bcall+5:
	  op -= Bcall;
	docall:
	  {
	    BEFORE_POTENTIAL_GC ();
	    DISCARD (op);
#ifdef BYTE_CODE_METER
	    if (byte_metering_on && SYMBOLP (TOP))
	      {
		Lisp_Object v1, v2;

		v1 = TOP;
		v2 = Fget (v1, Qbyte_code_meter);
		if (INTEGERP (v2)
		    && XINT (v2) < MOST_POSITIVE_FIXNUM)
		  {
		    XSETINT (v2, XINT (v2) + 1);
		    Fput (v1, Qbyte_code_meter, v2);
		  }
	      }
#endif
	    TOP = Ffuncall (op + 1, &TOP);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Bunbind+6:
	  op = FETCH;
	  goto dounbind;

	case Bunbind+7:
	  op = FETCH2;
	  goto dounbind;

	case Bunbind:
	case Bunbind+1:
	case Bunbind+2:
	case Bunbind+3:
	case Bunbind+4:
	case Bunbind+5:
	  op -= Bunbind;
	dounbind:
	  BEFORE_POTENTIAL_GC ();
	  unbind_to (SPECPDL_INDEX () - op, Qnil);
	  AFTER_POTENTIAL_GC ();
	  break;

	case Bunbind_all:
	  /* To unbind back to the beginning of this frame.  Not used yet,
	     but will be needed for tail-recursion elimination.  */
	  BEFORE_POTENTIAL_GC ();
	  unbind_to (count, Qnil);
	  AFTER_POTENTIAL_GC ();
	  break;

	case Bgoto:
	  MAYBE_GC ();
	  BYTE_CODE_QUIT;
	  op = FETCH2;    /* pc = FETCH2 loses since FETCH2 contains pc++ */
	  CHECK_RANGE (op);
	  stack.pc = stack.byte_string_start + op;
	  break;

	case Bgotoifnonnil:
	  {
	    Lisp_Object v1;
	    MAYBE_GC ();
	    op = FETCH2;
	    v1 = POP;
	    if (!NILP (v1))
	      {
		BYTE_CODE_QUIT;
		CHECK_RANGE (op);
		stack.pc = stack.byte_string_start + op;
	      }
	    break;
	  }

	case Bgotoifnilelsepop:
	  MAYBE_GC ();
	  op = FETCH2;
	  if (NILP (TOP))
	    {
	      BYTE_CODE_QUIT;
	      CHECK_RANGE (op);
	      stack.pc = stack.byte_string_start + op;
	    }
	  else DISCARD (1);
	  break;

	case Bgotoifnonnilelsepop:
	  MAYBE_GC ();
	  op = FETCH2;
	  if (!NILP (TOP))
	    {
	      BYTE_CODE_QUIT;
	      CHECK_RANGE (op);
	      stack.pc = stack.byte_string_start + op;
	    }
	  else DISCARD (1);
	  break;

	case BRgoto:
	  MAYBE_GC ();
	  BYTE_CODE_QUIT;
	  stack.pc += (int) *stack.pc - 127;
	  break;

	case BRgotoifnil:
	  {
	    Lisp_Object v1;
	    MAYBE_GC ();
	    v1 = POP;
	    if (NILP (v1))
	      {
		BYTE_CODE_QUIT;
		stack.pc += (int) *stack.pc - 128;
	      }
	    stack.pc++;
	    break;
	  }

	case BRgotoifnonnil:
	  {
	    Lisp_Object v1;
	    MAYBE_GC ();
	    v1 = POP;
	    if (!NILP (v1))
	      {
		BYTE_CODE_QUIT;
		stack.pc += (int) *stack.pc - 128;
	      }
	    stack.pc++;
	    break;
	  }

	case BRgotoifnilelsepop:
	  MAYBE_GC ();
	  op = *stack.pc++;
	  if (NILP (TOP))
	    {
	      BYTE_CODE_QUIT;
	      stack.pc += op - 128;
	    }
	  else DISCARD (1);
	  break;

	case BRgotoifnonnilelsepop:
	  MAYBE_GC ();
	  op = *stack.pc++;
	  if (!NILP (TOP))
	    {
	      BYTE_CODE_QUIT;
	      stack.pc += op - 128;
	    }
	  else DISCARD (1);
	  break;

	case Breturn:
	  result = POP;
	  goto exit;

	case Bdiscard:
	  DISCARD (1);
	  break;

	case Bconstant2:
	  PUSH (vectorp[FETCH2]);
	  break;

	case Bsave_excursion:
	  record_unwind_protect (save_excursion_restore,
				 save_excursion_save ());
	  break;

	case Bsave_current_buffer:
	case Bsave_current_buffer_1:
	  record_unwind_protect (set_buffer_if_live, Fcurrent_buffer ());
	  break;

	case Bsave_window_excursion:
	  BEFORE_POTENTIAL_GC ();
	  TOP = Fsave_window_excursion (TOP);
	  AFTER_POTENTIAL_GC ();
	  break;

	case Bsave_restriction:
	  record_unwind_protect (save_restriction_restore,
				 save_restriction_save ());
	  break;

	case Bcatch:
	  {
	    Lisp_Object v1;
	    BEFORE_POTENTIAL_GC ();
	    v1 = POP;
	    TOP = internal_catch (TOP, Feval, v1);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Bunwind_protect:
	  record_unwind_protect (Fprogn, POP);
	  break;

	case Bcondition_case:
	  {
	    Lisp_Object handlers, body;
	    handlers = POP;
	    body = POP;
	    BEFORE_POTENTIAL_GC ();
	    TOP = internal_lisp_condition_case (TOP, body, handlers);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Btemp_output_buffer_setup:
	  BEFORE_POTENTIAL_GC ();
	  CHECK_STRING (TOP);
	  temp_output_buffer_setup (SDATA (TOP));
	  AFTER_POTENTIAL_GC ();
	  TOP = Vstandard_output;
	  break;

	case Btemp_output_buffer_show:
	  {
	    Lisp_Object v1;
	    BEFORE_POTENTIAL_GC ();
	    v1 = POP;
	    temp_output_buffer_show (TOP);
	    TOP = v1;
	    /* pop binding of standard-output */
	    unbind_to (SPECPDL_INDEX () - 1, Qnil);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Bnth:
	  {
	    Lisp_Object v1, v2;
	    BEFORE_POTENTIAL_GC ();
	    v1 = POP;
	    v2 = TOP;
	    CHECK_NUMBER (v2);
	    AFTER_POTENTIAL_GC ();
	    op = XINT (v2);
	    immediate_quit = 1;
	    while (--op >= 0 && CONSP (v1))
	      v1 = XCDR (v1);
	    immediate_quit = 0;
	    TOP = CAR (v1);
	    break;
	  }

	case Bsymbolp:
	  TOP = SYMBOLP (TOP) ? Qt : Qnil;
	  break;

	case Bconsp:
	  TOP = CONSP (TOP) ? Qt : Qnil;
	  break;

	case Bstringp:
	  TOP = STRINGP (TOP) ? Qt : Qnil;
	  break;

	case Blistp:
	  TOP = CONSP (TOP) || NILP (TOP) ? Qt : Qnil;
	  break;

	case Bnot:
	  TOP = NILP (TOP) ? Qt : Qnil;
	  break;

	case Bcons:
	  {
	    Lisp_Object v1;
	    v1 = POP;
	    TOP = Fcons (TOP, v1);
	    break;
	  }

	case Blist1:
	  TOP = Fcons (TOP, Qnil);
	  break;

	case Blist2:
	  {
	    Lisp_Object v1;
	    v1 = POP;
	    TOP = Fcons (TOP, Fcons (v1, Qnil));
	    break;
	  }

	case Blist3:
	  DISCARD (2);
	  TOP = Flist (3, &TOP);
	  break;

	case Blist4:
	  DISCARD (3);
	  TOP = Flist (4, &TOP);
	  break;

	case BlistN:
	  op = FETCH;
	  DISCARD (op - 1);
	  TOP = Flist (op, &TOP);
	  break;

	case Blength:
	  BEFORE_POTENTIAL_GC ();
	  TOP = Flength (TOP);
	  AFTER_POTENTIAL_GC ();
	  break;

	case Baref:
	  {
	    Lisp_Object v1;
	    BEFORE_POTENTIAL_GC ();
	    v1 = POP;
	    TOP = Faref (TOP, v1);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Baset:
	  {
	    Lisp_Object v1, v2;
	    BEFORE_POTENTIAL_GC ();
	    v2 = POP; v1 = POP;
	    TOP = Faset (TOP, v1, v2);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Bsymbol_value:
	  BEFORE_POTENTIAL_GC ();
	  TOP = Fsymbol_value (TOP);
	  AFTER_POTENTIAL_GC ();
	  break;

	case Bsymbol_function:
	  BEFORE_POTENTIAL_GC ();
	  TOP = Fsymbol_function (TOP);
	  AFTER_POTENTIAL_GC ();
	  break;

	case Bset:
	  {
	    Lisp_Object v1;
	    BEFORE_POTENTIAL_GC ();
	    v1 = POP;
	    TOP = Fset (TOP, v1);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Bfset:
	  {
	    Lisp_Object v1;
	    BEFORE_POTENTIAL_GC ();
	    v1 = POP;
	    TOP = Ffset (TOP, v1);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Bget:
	  {
	    Lisp_Object v1;
	    BEFORE_POTENTIAL_GC ();
	    v1 = POP;
	    TOP = Fget (TOP, v1);
	    AFTER_POTENTIAL_GC ();
	    break;
	  }

	case Bsubstring:
	  {
	    Lisp_Object v1, v2;