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/*
* Copyright (C) 2000, Imperial College
*
* This file is part of the Imperial College Exact Real Arithmetic Library.
* See the copyright notice included in the distribution for conditions
* of use.
*/
#include <stdio.h>
#include "real.h"
#include "real-impl.h"
/*
* The conditional is implemented as a function:
*
* void * realAlt(Bool, *void, ...)
*
* where the arguments are a list of guard/value pairs. This is implemented
* using stdarg(3). The last guard must be the constant DEFAULT_GUARD.
*/
typedef struct ALT_CELL {
Bool guard;
void *value;
struct ALT_CELL *next;
} AltCell;
#include <stdarg.h>
/*
* ### A better scheme would be to put the alt in the heap as well. Perhaps
* later.
*/
void *
realAlt(Bool guard, void *value, ...)
{
va_list ap;
AltCell *head, *ptr;
AltCell **prev;
void *defaultValue;
void runStack();
/*
* The caller is a wally if the first argument is the default guard.
* But we accept it.
*/
if ((unsigned) guard == DEFAULT_GUARD)
return value;
if (guard->gen.tag.value == LAZY_TRUE)
return value;
if ((head = (AltCell *) alloca(sizeof(AltCell))) == NULL)
Error(FATAL, E_INT, "realAlt", "alloca failed");
head->guard = guard;
head->value = value;
head->next = NULL;
ptr = head;
/*
* Now we consume the arguments. Each is a guard/value pair. If
* the guard is true, then we just return the value. If not then
* we allocate a cell with the guard and value and add it to
* the list of cells.
*/
va_start(ap, value);
while ((unsigned) (guard = va_arg(ap, Bool)) != DEFAULT_GUARD) {
value = va_arg(ap, void *);
if (guard->gen.tag.value == LAZY_TRUE)
return value;
if ((ptr->next = (AltCell *) alloca(sizeof(AltCell))) == NULL)
Error(FATAL, E_INT, "realAlt", "alloca failed");
ptr = ptr->next;
ptr->guard = guard;
ptr->value = value;
ptr->next = NULL;
}
defaultValue = va_arg(ap, void *);
va_end(ap);
/*
* If we reach here, then we have a list of AltCells which
* have guards having value LAZY_UNKNOWN. We now walk down this
* list repeatedly. For each alternative, we force the next value
* in the boolean stream. If any guard becomes true, then we
* return the corresponding value. If something becomes false,
* it gets removed from the list. The loop ends when the list
* becomes empty whereupon we return the default value provided
* at the end of the argument list.
*/
ptr = head;
prev = &head;
while (ptr != NULL) {
if (ptr->guard->gen.tag.value == LAZY_UNKNOWN) {
PUSH_2(ptr->guard->gen.force, ptr->guard);
runStack();
}
switch (ptr->guard->gen.tag.value) {
case LAZY_TRUE :
return ptr->value;
break;
case LAZY_FALSE :
*prev = ptr->next; /* unlink the cell */
ptr = ptr->next;
break;
case LAZY_UNKNOWN :
prev = &(ptr->next);
ptr = ptr->next;
break;
default :
Error(FATAL, E_INT, "realAlt",
"invalid boolean value encountered");
break;
}
/*
* Reached the end of the list so start from the beginning again.
*/
if (ptr == NULL) {
ptr = head;
prev = &head;
}
}
return defaultValue;
}
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