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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"
/*
* Functions related to ``information overlap'' tensor strategy. Can
* probably be dropped and reky soley on epsilon-delta stuff.
*/
static mpz_t a_times_d, c_times_b;
void
initStrategy()
{
mpz_init(a_times_d);
mpz_init(c_times_b);
}
/*
* Given vectors (a,b) and (c,d), this returns
* -1 if (a,b) < (c,d)
* =0 if (a,b) = (c,d)
* +1 if (a,b) > (c,d)
*/
static int
compareVectors(Vector v0, Vector v1)
{
int tmp;
mpz_mul(a_times_d, v0[0], v1[1]);
mpz_mul(c_times_b, v1[0], v0[1]);
tmp = mpz_cmp(a_times_d, c_times_b);
return MPZ_SIGN(tmp);
}
/*
* This is Peter's ``information overlap'' strategy.
*
* If the structure of the code seems odd, it is because we want to avoid
* doing the same operations more than once. C guarantees that when evaluating
* a conjunction, if the first conjunct is false, then the second is
* not evaluated.
*
* This returns 1 to select y (right) and 0 to select x (left).
*/
int
tensorStrategy(Tensor t)
{
int v0cv1;
/*
* we compare:
* v0 <> v1
* v0 <> v3
* v2 <> v1
* v2 <> v3
*/
v0cv1 = compareVectors(t[0], t[1]);
if (v0cv1 > 0) {
if ((compareVectors(t[0], t[3]) > 0)
&& (compareVectors(t[2], t[1]) > 0)
&& (compareVectors(t[2], t[3]) > 0)) {
return 1;
}
else
return 0;
}
else {
if (v0cv1 < 0) {
if ((compareVectors(t[0], t[3]) < 0)
&& (compareVectors(t[2], t[1]) < 0)
&& (compareVectors(t[2], t[3]) < 0)) {
return 1;
}
else
return 0;
}
}
return 0;
}
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