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|
// file kernel/n/c/burnikel.c: Burnikel-Ziegler division
/*-----------------------------------------------------------------------+
| Copyright 2005-2006, Michel Quercia (michel.quercia@prepas.org) |
| |
| This file is part of Numerix. Numerix is free software; you can |
| redistribute it and/or modify it under the terms of the GNU Lesser |
| General Public License as published by the Free Software Foundation; |
| either version 2.1 of the License, or (at your option) any later |
| version. |
| |
| The Numerix Library 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 |
| Lesser General Public License for more details. |
| |
| You should have received a copy of the GNU Lesser General Public |
| License along with the GNU MP Library; see the file COPYING. If not, |
| write to the Free Software Foundation, Inc., 59 Temple Place - |
| Suite 330, Boston, MA 02111-1307, USA. |
+-----------------------------------------------------------------------+
| |
| Division de Burnikel et Ziegler |
| |
+-----------------------------------------------------------------------*/
/* +------------+
| Division |
+------------+ */
/*
entre :
a = naturel de longueur lc+lb
b = naturel de longueur lb
c = naturel de longueur lc
contraintes :
lb >= 2, lc > 0, le bit de poids fort de b est non nul,
a < BASE^lc*b
a,b,c non confondus
sortie :
a <- a mod b
c <- floor(a/b)
*/
#ifndef assembly_sn_burnidiv
#ifdef debug_burnidiv
void xn(burnidiv_buggy)
#else
void xn(burnidiv)
#endif
(chiffre *a, long lc, chiffre *b, long lb, chiffre *c) {
long p,q,r;
chiffre *x;
/* petite division => div_n2 */
if ((lb <= burnidiv_lim) || (lc <= div_small_c_lim)) {xn(div_n2)(a,lc,b,lb,c); return;}
/* cas rcursif, dcoupe b en deux et divise par tranches de q chiffres */
p = lb/2; q = lb-p;
r = lc%q; if (r == 0) r = q;
x = xn(alloc_tmp)(lb);
lc -= r; a += lc; c += lc;
while(lc>=0) {
/* divise a1 par b1 en tronquant le quotient BASE^r - 1 */
if (xn(cmp)(a+p+r,q,b+p,q)) xn(burnidiv)(a+p,r, b+p,q, c);
else {
xn(clear)(a+p+r,q);
xn(inc)(a+p,q+r,b+p,q);
xn(fill)(c,r);
}
/* a0 + BASE^p*r1 -= c*b0, et corrige si < 0 */
if (r < p) xn(toommul)(b,p,c,r,x); else xn(toommul)(c,r,b,p,x);
if (xn(dec)(a,lb+1,x,p+r)) {
do xn(dec1)(c,r); while (xn(inc)(a,lb+1,b,lb) == 0);
}
/* tranche de q chiffres suivante */
a -= q; c -= q; lc -= q; r = q;
}
xn(free_tmp)(x);
}
#endif /* assembly_sn_burnidiv */
/* +------------+
| Contrle |
+------------+ */
#ifdef debug_burnidiv
void xn(burnidiv_buggy)(chiffre *a, long la, chiffre *b, long lb, chiffre *c);
void xn(burnidiv)(chiffre *a, long lc, chiffre *b, long lb, chiffre *c) {
long la = lc+lb;
chiffre *x, *y;
x = xn(alloc_tmp)(2*la); y = x+la;
/* validit des longueurs ? */
if ((lb < 2) || (la < lb))
xn(internal_error)("error, burnidiv is called with lb < 2 or la < lb",0);
/* le bit de poids fort de b est non nul ? */
if ((b[lb-1] & BASE_2) == 0)
xn(internal_error)("error, burnidiv is called with msb(b) = 0",0);
/* a < BASE^lc*b ? */
if (xn(cmp)(a+lc,lb,b,lb) >= 0)
xn(internal_error)("error, burnidiv is called with a >= BASE^lc*b",2,a,la,b,lb);
/* effectue la division douteuse */
xn(move)(a,la,x);
xn(burnidiv_buggy)(a,lc,b,lb,c);
/* a_entre = a_sortie + b*c et a_sortie < b ?*/
if (lc < lb) xn(toommul)(b,lb,c,lc,y); else xn(toommul)(c,lc,b,lb,y);
if ( (xn(inc)(y,la,a,lb) != 0)
|| (xn(cmp)(x,la,y,la) != 0)
|| (xn(cmp)(a,la,b,lb) >= 0)) {
xn(internal_error)("error in burnidiv", 4,x,la,b,lb,a,la,c,lc);
}
xn(free_tmp)(x);
}
#endif /* debug_burnidiv */
|
