203 lines
5.1 KiB
C
203 lines
5.1 KiB
C
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/*
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*
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* c o n t . c -- Continuations management
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*
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* Copyright <EFBFBD> 1993-1996 Erick Gallesio - I3S-CNRS/ESSI <eg@unice.fr>
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*
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*
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* Permission to use, copy, and/or distribute this software and its
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* documentation for any purpose and without fee is hereby granted, provided
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* that both the above copyright notice and this permission notice appear in
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* all copies and derived works. Fees for distribution or use of this
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* software or derived works may only be charged with express written
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* permission of the copyright holder.
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* This software is provided ``as is'' without express or implied warranty.
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*
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* This software is a derivative work of other copyrighted softwares; the
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* copyright notices of these softwares are placed in the file COPYRIGHTS
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*
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*
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* Author: Erick Gallesio [eg@kaolin.unice.fr]
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* Creation date: 8-Nov-1993 11:34
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* Last file update: 26-Apr-1996 17:46
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*/
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#include "stk.h"
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#include "gc.h"
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#ifdef sparc
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#define FLUSH_REGISTERS_WINDOW() asm("t 0x3") /* Stolen in Elk 2.0 source */
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#else
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#define FLUSH_REGISTERS_WINDOW()
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#endif
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struct cont {
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jmp_buf env;
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SCM wind_stack;
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SCM *start;
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unsigned length;
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SCM stack[1];
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};
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#define C_ENV(x) (((struct cont *)((x)->storage_as.cont.data))->env)
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#define C_START(x) (((struct cont *)((x)->storage_as.cont.data))->start)
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#define C_LEN(x) (((struct cont *)((x)->storage_as.cont.data))->length)
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#define C_STACK(x) (((struct cont *)((x)->storage_as.cont.data))->stack)
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#define C_WIND_STACK(x) (((struct cont *)((x)->storage_as.cont.data))->wind_stack)
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static SCM call_cc_escaped_value;
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/* Don't allocate these vars on stack */
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static SCM *from, *to;
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static long length;
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static int i;
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static void unwind(SCM stop, int n);
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static int get_stack_length(void)
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{
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SCM stack_limit;
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return (&stack_limit < STk_stack_start_ptr) ? STk_stack_start_ptr - &stack_limit
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: &stack_limit - STk_stack_start_ptr;
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}
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static SCM prepare_call_cc(SCM proc)
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{
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SCM z;
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if (STk_procedurep(proc) == Ntruth)
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Err("call-with-current-continuation: Bad procedure", proc);
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/* Find the start adress and the length of the stack to save */
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length = get_stack_length();
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from = (STk_stack_start_ptr<&z) ? STk_stack_start_ptr
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: STk_stack_start_ptr-length;
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/* Allocate a new object for this continuation */
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NEWCELL(z, tc_cont);
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z->storage_as.cont.data = must_malloc(sizeof(struct cont) + length * sizeof(SCM));
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C_START(z) = from;
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C_LEN(z) = length;
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C_WIND_STACK(z) = STk_wind_stack;
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FLUSH_REGISTERS_WINDOW();
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for (i=length, to = C_STACK(z); i--; ) *to++ = *from++;
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return z;
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}
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SCM STk_mark_continuation(SCM cont)
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{
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STk_mark_stack((SCM *)C_STACK(cont), (SCM *)(C_STACK(cont)+C_LEN(cont)-1));
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return C_WIND_STACK(cont);
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}
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SCM STk_do_call_cc(SCM *x)
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{
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SCM tmp;
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tmp = prepare_call_cc(*x);
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/* Use a setjmp/longjmp for the continuation */
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if (setjmp(C_ENV(tmp)) == 0) {
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*x = LIST2(*x, tmp);
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return Truth;
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}
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else
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return (*x=call_cc_escaped_value);
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}
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void STk_throw(SCM fct, SCM val)
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{
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static SCM tmp;
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union {
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SCM stack_end;
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SCM hole[1024]; /* Reserve 1K-pointers on stack */
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}u;
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/* Evaluate room on stack. If not enough call throw again to alloc. a new hole */
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if (&u.stack_end < STk_stack_start_ptr) {
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/* Stack grows downward */
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if (&u.stack_end > C_START(fct)) STk_throw(fct, val);
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}
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else {
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/* Stack grows upward */
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if (&u.stack_end < C_START(fct)+ C_LEN(fct)) STk_throw(fct, val);
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}
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/* Take care of active dynamic-winds */
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tmp = C_WIND_STACK(fct);
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unwind(tmp, STk_llength(STk_wind_stack) - STk_llength(tmp));
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/* Save val in a global and reset stack as it was before calling call/cc */
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call_cc_escaped_value = val; tmp = fct;
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FLUSH_REGISTERS_WINDOW();
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for(to=C_START(fct), from=C_STACK(fct), i=C_LEN(fct); i--; ) *to++ = *from++;
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/* And Go! */
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longjmp(C_ENV(tmp), JMP_THROW);
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}
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PRIMITIVE STk_continuationp(SCM obj)
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{
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return CONTINUATIONP(obj)? Truth: Ntruth;
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}
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/******************************************************************************
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*
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* Dynamic wind
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*
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******************************************************************************/
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void STk_unwind_all(void)
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{
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SCM p;
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for (p = STk_wind_stack; NNULLP(p); p = CDR(p)) {
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STk_wind_stack = CDR(p);
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Apply(CAR(CDR(CAR(p))), NIL);
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}
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}
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static void unwind(SCM stop, int n)
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{
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if (STk_wind_stack != stop) {
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if (n < 0) {
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unwind(CDR(stop),n+1);
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Apply(CAR(CAR(stop)),NIL);
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STk_wind_stack = stop;
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}
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else {
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SCM old_wind_stack = STk_wind_stack;
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STk_wind_stack = CDR(STk_wind_stack);
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Apply(CAR(CDR(CAR(old_wind_stack))), NIL);
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unwind(stop, n-1);
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}
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}
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}
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static void test_procedure(SCM thunk)
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{
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if (!STk_is_thunk(thunk)) Err("dynamic-wind: bad procedure", thunk);
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}
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PRIMITIVE STk_dynamic_wind(SCM thunk1, SCM thunk2, SCM thunk3)
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{
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SCM result;
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test_procedure(thunk1);
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test_procedure(thunk2);
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test_procedure(thunk3);
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Apply(thunk1, NIL);
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STk_wind_stack = Cons(LIST2(thunk1, thunk3), STk_wind_stack);
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result = Apply(thunk2, NIL);
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STk_wind_stack = CDR(STk_wind_stack);
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Apply(thunk3, NIL);
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return result;
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}
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