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Fix free list construction in new cons page to explicitly initialize ALL cons cells on the page (Ref issue #34)
Update comments, correct spelling errors, simplify style, note some areas for future work. modified: src/conspage.c
This commit is contained in:
Nick Briggs
parent
b1790bb7fe
commit
a5e70206fc
122
src/conspage.c
122
src/conspage.c
@ -11,11 +11,10 @@ static char *id = "$Id: conspage.c,v 1.3 1999/05/31 23:35:27 sybalsky Exp $ Copy
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#include "version.h"
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/***********************************************************************/
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/*
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File Name :conspage.c
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*/
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/************************************************************************/
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/**
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* @file conspage.c
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*/
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#include "lispemul.h"
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#include "address.h"
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#include "adr68k.h"
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@ -31,47 +30,39 @@ static char *id = "$Id: conspage.c,v 1.3 1999/05/31 23:35:27 sybalsky Exp $ Copy
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#include "commondefs.h"
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#include "gchtfinddefs.h"
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/************************************************************************/
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/* */
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/* i n i t _ c o n s p a g e */
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/* */
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/* Initialize a fresh page of CONS cells. Sets the count field */
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/* and chains the cells together for ease of searching. */
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/* */
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/* A fresh CONS page looks like this: */
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/* */
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/* +--------+--------+----------------+ */
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/* 0 | count | nxtcell| (padding) | nxtcell = 254. */
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/* +--------+--------+----------------+ */
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/* 2 | next_page | */
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/* +--------+-------------------------+ */
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/* 4 | 0 | N I L | */
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/* +--------+-------------------------+ */
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/* 6 | 4 | N I L | */
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/* +--------+-------------------------+ */
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/* ... | ... | N I L | */
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/* +--------+-------------------------+ */
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/* 254 | 252 | N I L | */
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/* +--------+-------------------------+ */
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/* */
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/* The cells are chained together thru their high 8 bits, */
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/* using the word offset within page as the chain. Cells */
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/* are chained from the top of the page down. */
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/* */
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/* Experimental version goes nxtcell = 248 */
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/* count/nxtcell in cell 4, next_page in cell 6
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/**
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* Initializes a page of CONS cells, sets up the free count and
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* chains the cells together for ease of searching.
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*
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* A fresh CONS page looks like this:
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*
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* +--------+--------+----------------+
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* 0 | count |nextcell| (padding) | nextcell = 254.
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* +--------+--------+----------------+
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* 2 | next_page |
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* +--------+-------------------------+
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* 4 | 0 | N I L |
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* +--------+-------------------------+
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* 6 | 4 | N I L |
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* +--------+-------------------------+
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* ... | ... | N I L |
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* +--------+-------------------------+
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* 254 | 252 | N I L |
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* +--------+-------------------------+
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*
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* The cells are chained together thru their high 8 bits,
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* using the (16-bit) word offset within page as the chain.
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* Cells are chained from the top of the page down.
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*
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* Experimental version goes nextcell = 248
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* count/nextcell in cell 4, next_page in cell 6
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* Chain up 4 down 8 ( ^ 6 into word count)
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*
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* @param[in,out] base Native pointer to cons page
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* @param[in] link Lisp page number of next cons page
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*/
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/* Chain up 4 down 8 ( ^ 6 into word count)
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*/
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/* */
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/* */
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/* */
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/* */
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/************************************************************************/
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static void init_conspage(register struct conspage *base, unsigned int link)
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/* Page Base */
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/* Prev Link page number DL->int*/
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{
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register ConsCell *cell;
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register int j; /* DL-> int */
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@ -81,22 +72,29 @@ static void init_conspage(register struct conspage *base, unsigned int link)
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#endif
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#ifdef NEWCDRCODING
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base->next_cell = 6 ^ (j = 254);
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j = 254;
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base->next_cell = 6 ^ j;
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while (j > 8) {
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cell = (ConsCell *)((DLword *)base + (6 ^ j));
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cell->car_field = NIL_PTR;
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j -= 2;
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((freecons *)cell)->next_free = (6 ^ j);
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}
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cell = (ConsCell *)((DLword *)base + (6 ^ j));
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cell->car_field = NIL_PTR;
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((freecons *)cell)->next_free = 0;
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base->count = 124;
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#else
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base->next_cell = j = 254;
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while (j != 0) {
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cell = (ConsCell *)((DLword *)base + (j));
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cell = (ConsCell *)((DLword *)base + j);
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cell->car_field = NIL_PTR;
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j -= 2;
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((freecons *)cell)->next_free = (j);
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((freecons *)cell)->next_free = j;
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}
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cell = (ConsCell *)((DLword *)base + j);
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cell->car_field = NIL_PTR;
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((freecons *)cell)->next_free = 0;
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base->count = 127;
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#endif /* NEWCDRCODING */
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base->next_page = link;
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@ -127,12 +125,12 @@ struct conspage *next_conspage(void) {
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register int next, prior;
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#ifdef NEWCDRCODING
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/* Alloc 2 Conspages and get 1st page base */
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/* Allocate 2 conspages and get 1st page base */
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page1 = (struct conspage *)alloc_mdspage(TYPE_LISTP);
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/* Culc. next Conspage's Base address */
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/* Calculate next conspage's base address */
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page2 = (struct conspage *)((DLword *)page1 + DLWORDSPER_PAGE);
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init_conspage(page2, 0); /* Doesn't exst next page */
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init_conspage(page2, 0); /* No next page */
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init_conspage(page1, LPAGE_from_68k(page2));
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prior = 0;
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@ -151,16 +149,19 @@ struct conspage *next_conspage(void) {
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if (page2->next_page) error("page2 has a next page??");
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if (page2 == priorpg) error("loop in conspage next_pages");
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#else
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for (next = (int)ListpDTD->dtd_nextpage; /* getnext free conspage */
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for (next = (int)ListpDTD->dtd_nextpage; /* /!\ Note no exit condition /!\ */ /* get next free conspage */
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; ListpDTD->dtd_nextpage = next = page1->next_page, page1->next_page = 0xffff) {
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if (next == 0) {
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/* Alloc 2 Conspages and get 1st page base */
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/* Allocate 2 conspages and get 1st page base */
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page1 = (struct conspage *)alloc_mdspage(TYPE_LISTP);
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/* Culc. next Conspage's Base address */
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/* Calculate next conspage's base address */
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page2 = (struct conspage *)((DLword *)page1 + DLWORDSPER_PAGE);
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init_conspage(page2, ListpDTD->dtd_nextpage); /* Doesn't exst next page */
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/* XXX: why is the link for page2's next here?
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* when it was previously commented as "Doesn't exst next page"
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*/
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init_conspage(page2, ListpDTD->dtd_nextpage);
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init_conspage(page1, LPAGE_from_68k(page2));
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ListpDTD->dtd_nextpage = LPAGE_from_68k(page1);
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@ -179,15 +180,14 @@ ex:
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/************************************************************************/
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/* */
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/* f i n d _ c d r c o d a b l e _ p a i r */
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/* f i n d _ c d r c o d a b l e _ p a i r */
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/* */
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/* Find a pair of CONS cells that are close enough (within 7) */
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/* that the second can be cdr-coded as the cdr of the first. */
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/* Set up the cdr code in the first cell, and return it.
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*/
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/* Find a pair of CONS cells that are close enough (within 7) */
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/* that the second can be cdr-coded as the cdr of the first. */
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/* Set up the cdr code in the first cell, and return it. */
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/* */
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/* First searches the CONS page given, then the free-page chain */
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/* finally, calls conspage to get a fresh (and guaranteed useful) page. */
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/* First searches the CONS page given, then the free-page chain */
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/* finally, calls conspage to get a fresh (and guaranteed useful) page.*/
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/* */
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/************************************************************************/
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@ -302,8 +302,6 @@ LispPTR N_OP_cons(register int cons_car, register int cons_cdr) {
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register ConsCell *new_cell, *temp_cell;
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register int new_page; /* hold the return val of nextconspage ,DL->int */
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extern ConsCell *find_close_prior_cell(struct conspage * page, LispPTR oldcell);
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GCLOOKUP(cons_cdr &= POINTERMASK, ADDREF);
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GCLOOKUP(cons_car, ADDREF);
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