macssh/gmp/mpfr/add.c

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2001-03-07 09:55:27 +00:00
/* mpfr_add -- add two floating-point numbers
Copyright (C) 1999 PolKA project, Inria Lorraine and Loria
This file is part of the MPFR Library.
The MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Library General Public License as published by
the Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
The MPFR 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 Library General Public
License for more details.
You should have received a copy of the GNU Library General Public License
along with the MPFR Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include <stdio.h>
#include "gmp.h"
#include "gmp-impl.h"
#include "mpfr.h"
extern void mpfr_sub1 _PROTO((mpfr_ptr, mpfr_srcptr, mpfr_srcptr,
unsigned char, int));
#define ONE ((mp_limb_t) 1)
/* signs of b and c are supposed equal,
diff_exp is the difference between the exponents of b and c,
which is supposed >= 0 */
void
#if __STDC__
mpfr_add1(mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c,
unsigned char rnd_mode, int diff_exp)
#else
mpfr_add1(a, b, c, rnd_mode, diff_exp)
mpfr_ptr a;
mpfr_srcptr b;
mpfr_srcptr c;
unsigned char rnd_mode;
int diff_exp;
#endif
{
mp_limb_t *ap, *bp, *cp, cc, c2, c3=0; unsigned int an,bn,cn; int sh,dif,k;
TMP_DECL(marker);
TMP_MARK(marker);
ap = MANT(a);
bp = MANT(b);
cp = MANT(c);
if (ap == bp) {
bp = (mp_ptr) TMP_ALLOC(ABSSIZE(b) * BYTES_PER_MP_LIMB);
MPN_COPY (bp, ap, ABSSIZE(b));
if (ap == cp) { cp = bp; }
}
else if (ap == cp)
{
cp = (mp_ptr) TMP_ALLOC (ABSSIZE(c) * BYTES_PER_MP_LIMB);
MPN_COPY(cp, ap, ABSSIZE(c));
}
an = (PREC(a)-1)/mp_bits_per_limb+1; /* number of significant limbs of a */
sh = an*mp_bits_per_limb-PREC(a); /* non-significant bits in low limb */
bn = (PREC(b)-1)/mp_bits_per_limb+1; /* number of significant limbs of b */
EXP(a) = EXP(b);
if (SIGN(a)!=SIGN(b)) CHANGE_SIGN(a);
/* case 1: diff_exp>=prec(a), i.e. c only affects the last bit
through rounding */
dif = PREC(a)-diff_exp;
if (dif<=0) {
/* diff_exp>=PREC(a): c does not overlap with a */
/* either PREC(b)<=PREC(a), and we can copy the mantissa of b directly
into that of a, or PREC(b)>PREC(a) and we have to round b+c */
if (PREC(b)<=PREC(a)) {
MPN_COPY(ap+(an-bn), bp, bn);
/* fill low significant limbs with zero */
for (bp=ap;bn<an;bn++) *bp++=0;
/* now take c into account */
if (rnd_mode==GMP_RNDN) {
/* to nearest */
/* if diff_exp > PREC(a), no change */
if (diff_exp==PREC(a)) {
/* if c is not zero, then as it is normalized, we have to add
one to the lsb of a if c>1/2, or c=1/2 and lsb(a)=1 (round to
even) */
if (NOTZERO(c)) {
/* c is not zero */
/* check whether mant(c)=1/2 or not */
cc = *cp - (ONE<<(mp_bits_per_limb-1));
if (cc==0) {
bp = cp+(PREC(c)-1)/mp_bits_per_limb;
while (cp<bp && cc==0) cc = *++cp;
}
if (cc || (ap[an-1] & (ONE<<sh))) goto add_one_ulp;
/* mant(c) != 1/2 or mant(c) = 1/2: add 1 iff lsb(a)=1 */
}
}
}
else if ((ISNONNEG(b) && rnd_mode==GMP_RNDU) ||
(ISNEG(b) && rnd_mode==GMP_RNDD)) {
/* round up */
if (NOTZERO(c)) goto add_one_ulp;
}
/* in the other cases (round to zero, or up/down with sign -/+),
nothing to do */
}
else {
/* PREC(b)>PREC(a) : we have to round b+c */
k=bn-an;
/* first copy the 'an' most significant limbs of b to a */
MPN_COPY(ap, bp+k, an);
if (rnd_mode==GMP_RNDN) {
/* to nearest */
/* first check whether the truncated bits from b are 1/2*lsb(a) */
if (sh) {
cc = *ap & ((ONE<<sh)-1);
*ap &= ~cc; /* truncate last bits */
cc -= ONE<<(sh-1);
}
else /* no bit to truncate */
cc = bp[--k] - (ONE<<(mp_bits_per_limb-1));
if ((long)cc>0) goto add_one_ulp; /* trunc(b)>1/2*lsb(a) -> round up */
else if (cc==0) {
while (k>1 && cc==0) cc=bp[--k];
/* now if the truncated part of b = 1/2*lsb(a), check whether c=0 */
if (NOTZERO(c) || (*ap & (ONE<<sh))) goto add_one_ulp;
/* if trunc(b)+c is exactly 1/2*lsb(a) : round to even lsb */
}
/* if cc<0 : trunc(b) < 1/2*lsb(a) -> round down, i.e. do nothing */
}
else if ((ISNONNEG(b) && rnd_mode==GMP_RNDU) ||
(ISNEG(b) && rnd_mode==GMP_RNDD)) {
/* first check whether trunc(b)+c is zero or not */
if (sh) {
cc = *ap & ((ONE<<sh)-1); *ap &= ~cc; /* truncate last bits */
}
else cc = bp[--k] - (ONE<<(mp_bits_per_limb-1));
while (cc==0 && k>1) cc=bp[--k];
if (cc || NOTZERO(c)) goto add_one_ulp;
}
/* in the other cases (round to zero, or up/down with sign -/+),
nothing to do, since b and c don't overlap, there can't be any
carry */
}
}
else {
/* diff_exp < PREC(a) : c overlaps with a by dif bits */
/* first copy upper part of c into a (after shift) */
unsigned char overlap;
k = (dif-1)/mp_bits_per_limb + 1; /* only the highest k limbs from c
have to be considered */
cn = (PREC(c)-1)/mp_bits_per_limb + 1;
MPN_ZERO(ap+k, an-k); /* do it now otherwise ap[k] may be destroyed
in case dif<0 */
if (dif<=PREC(c)) {
/* c has to be truncated */
dif = dif % mp_bits_per_limb;
dif = (dif) ? mp_bits_per_limb-dif-sh : -sh;
/* we have to shift by dif bits to the right */
if (dif>0) mpn_rshift(ap, cp+(cn-k), k, dif);
else if (dif<0) {
ap[k] = mpn_lshift(ap, cp+(cn-k), k, -dif);
/* put the non-significant bits in low limb for further rounding */
if (cn >= k+1)
ap[0] += cp[cn-k-1]>>(mp_bits_per_limb+dif);
}
else MPN_COPY(ap, cp+(cn-k), k);
overlap=1;
}
else {
/* c is not truncated, but we have to fill low limbs with 0 */
k = diff_exp/mp_bits_per_limb;
overlap = diff_exp%mp_bits_per_limb;
/* warning: a shift of zero bit is not allowed */
MPN_ZERO(ap, an-k-cn);
if (overlap) {
cc=mpn_rshift(ap+(an-k-cn), cp, cn, overlap);
if (an-k-cn>0) ap[an-k-cn-1]=cc;
}
else MPN_COPY(ap+(an-k-cn), cp, cn);
overlap=0;
}
/* here overlap=1 iff ulp(c)<ulp(a) */
/* then put high limbs to zero */
/* now add 'an' upper limbs of b in place */
if (PREC(b)<=PREC(a)) {
overlap += 2;
cc = mpn_add_n(ap+(an-bn), ap+(an-bn), bp, bn);
}
else
/* PREC(b) > PREC(a): we have to truncate b */
cc = mpn_add_n(ap, ap, bp+(bn-an), an);
if (cc) {
/* shift one bit to the right */
c3 = (ap[0]&1) && (PREC(a)%mp_bits_per_limb==0);
mpn_rshift(ap, ap, an, 1);
ap[an-1] += ONE<<(mp_bits_per_limb-1);
EXP(a)++;
}
/* remains to do the rounding */
if (rnd_mode==GMP_RNDN) {
/* to nearest */
int kc;
/* four cases: overlap =
(0) PREC(b) > PREC(a) and diff_exp+PREC(c) <= PREC(a)
(1) PREC(b) > PREC(a) and diff_exp+PREC(c) > PREC(a)
(2) PREC(b) <= PREC(a) and diff_exp+PREC(c) <= PREC(a)
(3) PREC(b) <= PREC(a) and diff_exp+PREC(c) > PREC(a) */
switch (overlap)
{
case 1: /* both b and c to round */
kc = cn-k; /* remains kc limbs from c */
k = bn-an; /* remains k limbs from b */
/* truncate last bits and store the difference with 1/2*ulp in cc */
cc = *ap & ((ONE<<sh)-1);
*ap &= ~cc; /* truncate last bits */
cc -= ONE<<(sh-1);
while ((cc==0 || cc==-1) && k!=0 && kc!=0) {
kc--;
cc += mpn_add_1(&c2, bp+(--k), 1,(cp[kc+1]<<(mp_bits_per_limb-dif))
+(cp[kc]>>dif));
if (cc==0 || cc==-1) cc=c2;
}
if ((long)cc>0) goto add_one_ulp;
else if ((long)cc<-1)
{ TMP_FREE(marker); return; /* the carry can be at most 1 */ }
else if (kc==0) goto round_b;
/* else round c: go through */
case 3: /* only c to round */
bp=cp; k=cn-k; goto to_nearest;
case 0: /* only b to round */
round_b:
k=bn-an; dif=0; goto to_nearest;
/* otherwise the result is exact: nothing to do */
}
}
else if ((ISNONNEG(b) && rnd_mode==GMP_RNDU) ||
(ISNEG(b) && rnd_mode==GMP_RNDD)) {
cc = *ap & ((ONE<<sh)-1);
*ap &= ~cc; /* truncate last bits */
if (cc || c3) goto add_one_ulp; /* will happen most of the time */
else {
/* same four cases too */
int kc = cn-k; /* remains kc limbs from c */
switch (overlap)
{
case 1: /* both b and c to round */
k = bn-an; /* remains k limbs from b */
while (cc==0 && k!=0 && kc!=0) {
kc--;
cc = mpn_add_1(&c2, bp+(--k), 1,(cp[kc+1]<<(mp_bits_per_limb-dif))
+ (cp[kc]>>dif));
}
if (cc) goto add_one_ulp;
else if (kc==0) goto round_b2;
/* else round c: go through */
case 3: /* only c to round */
while (kc) if (cp[--kc]) goto add_one_ulp;
/* if dif>0 : remains to check last dif bits from c */
if (dif>0 && (cp[0]<<(mp_bits_per_limb-dif))) goto add_one_ulp;
break;
case 0: /* only b to round */
round_b2:
k=bn-an;
while (k) if (bp[--k]) goto add_one_ulp;
/* otherwise the result is exact: nothing to do */
}
}
}
/* else nothing to do: round towards zero, i.e. truncate last sh bits */
else
*ap &= ~((ONE<<sh)-1);
}
goto end_of_add;
to_nearest: /* 0 <= sh < mp_bits_per_limb : number of bits of a to truncate
bp[k] : last significant limb from b */
if (sh) {
cc = *ap & ((ONE<<sh)-1);
*ap &= ~cc; /* truncate last bits */
c2 = ONE<<(sh-1);
}
else /* no bit to truncate */
{ if (k) cc = bp[--k]; else cc = 0; c2 = ONE<<(mp_bits_per_limb-1); }
if (cc>c2) goto add_one_ulp; /* trunc(b)>1/2*lsb(a) -> round up */
else if (cc==c2) {
cc=0; while (k && cc==0) cc=bp[--k];
/* special case of rouding c shifted to the right */
if (cc==0 && dif>0) cc=cp[0]<<(mp_bits_per_limb-dif);
/* now if the truncated part of b = 1/2*lsb(a), check whether c=0 */
if (cc || (*ap & (ONE<<sh))) goto add_one_ulp;
}
goto end_of_add;
add_one_ulp: /* add one unit in last place to a */
cc = mpn_add_1(ap, ap, an, ONE<<sh);
if (cc) { fprintf(stderr, "carry(3) in mpfr_add\n"); exit(1); }
end_of_add:
TMP_FREE(marker);
return;
}
void
#if __STDC__
mpfr_add(mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c,
unsigned char rnd_mode)
#else
mpfr_add(a, b, c, rnd_mode)
mpfr_ptr a;
mpfr_srcptr b;
mpfr_srcptr c;
unsigned char rnd_mode;
#endif
{
int diff_exp;
if (FLAG_NAN(b) || FLAG_NAN(c)) {
SET_NAN(a); return;
}
if (!NOTZERO(b)) { mpfr_set(a, c, rnd_mode); return; }
if (!NOTZERO(c)) { mpfr_set(a, b, rnd_mode); return; }
diff_exp = EXP(b)-EXP(c);
if (SIGN(b) != SIGN(c)) { /* signs differ, it's a subtraction */
if (diff_exp<0) {
mpfr_sub1(a, c, b, rnd_mode, -diff_exp);
}
else if (diff_exp>0) mpfr_sub1(a, b, c, rnd_mode, diff_exp);
else { /* diff_exp=0 */
diff_exp = mpfr_cmp3(b,c,-1);
/* if b>0 and diff_exp>0 or b<0 and diff_exp<0: abs(b) > abs(c) */
if (diff_exp==0) SET_ZERO(a);
else if (diff_exp*SIGN(b)>0) mpfr_sub1(a, b, c, rnd_mode, 0);
else mpfr_sub1(a, c, b, rnd_mode, 0);
}
}
else /* signs are equal, it's an addition */
if (diff_exp<0) mpfr_add1(a, c, b, rnd_mode, -diff_exp);
else mpfr_add1(a, b, c, rnd_mode, diff_exp);
}