Annotation of OpenXM_contrib/gmp/mpfr/div_ui.c, Revision 1.1.1.2
1.1 maekawa 1: /* mpfr_div_ui -- divide a floating-point number by a machine integer
2:
1.1.1.2 ! ohara 3: Copyright 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
1.1 maekawa 4:
5: This file is part of the MPFR Library.
6:
7: The MPFR Library is free software; you can redistribute it and/or modify
1.1.1.2 ! ohara 8: it under the terms of the GNU Lesser General Public License as published by
! 9: the Free Software Foundation; either version 2.1 of the License, or (at your
1.1 maekawa 10: option) any later version.
11:
12: The MPFR Library is distributed in the hope that it will be useful, but
13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
1.1.1.2 ! ohara 14: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
1.1 maekawa 15: License for more details.
16:
1.1.1.2 ! ohara 17: You should have received a copy of the GNU Lesser General Public License
1.1 maekawa 18: along with the MPFR Library; see the file COPYING.LIB. If not, write to
19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
20: MA 02111-1307, USA. */
21:
22: #include <stdio.h>
23: #include "gmp.h"
24: #include "gmp-impl.h"
1.1.1.2 ! ohara 25: #include "longlong.h"
1.1 maekawa 26: #include "mpfr.h"
1.1.1.2 ! ohara 27: #include "mpfr-impl.h"
1.1 maekawa 28:
29: /* returns 0 if result exact, non-zero otherwise */
30: int
1.1.1.2 ! ohara 31: mpfr_div_ui (mpfr_ptr y, mpfr_srcptr x, unsigned long int u, mp_rnd_t rnd_mode)
1.1 maekawa 32: {
1.1.1.2 ! ohara 33: long int xn, yn, dif, sh, i;
! 34: mp_limb_t *xp, *yp, *tmp, c, d;
! 35: int inexact, middle = 1;
1.1 maekawa 36: TMP_DECL(marker);
37:
1.1.1.2 ! ohara 38: if (MPFR_IS_NAN(x))
! 39: {
! 40: MPFR_SET_NAN(y);
! 41: MPFR_RET_NAN;
! 42: }
! 43:
! 44: MPFR_CLEAR_NAN(y); /* clear NaN flag */
! 45:
! 46: if (MPFR_IS_INF(x))
! 47: {
! 48: MPFR_SET_INF(y);
! 49: MPFR_SET_SAME_SIGN(y, x);
! 50: MPFR_RET(0);
! 51: }
! 52:
! 53: if (u == 0)
! 54: {
! 55: if (MPFR_IS_ZERO(x)) /* 0/0 is NaN */
! 56: {
! 57: MPFR_SET_NAN(y);
! 58: MPFR_RET_NAN;
! 59: }
! 60: else /* x/0 is Inf */
! 61: {
! 62: MPFR_SET_INF(y);
! 63: MPFR_SET_SAME_SIGN(y, x);
! 64: MPFR_RET(0);
! 65: }
! 66: }
! 67:
! 68: MPFR_CLEAR_INF(y);
! 69: MPFR_SET_SAME_SIGN(y, x);
! 70:
! 71: if (MPFR_IS_ZERO(x))
! 72: {
! 73: MPFR_SET_ZERO(y);
! 74: MPFR_RET(0);
! 75: }
1.1 maekawa 76:
77: TMP_MARK(marker);
1.1.1.2 ! ohara 78: xn = (MPFR_PREC(x) - 1)/BITS_PER_MP_LIMB + 1;
! 79: yn = (MPFR_PREC(y) - 1)/BITS_PER_MP_LIMB + 1;
1.1 maekawa 80:
1.1.1.2 ! ohara 81: xp = MPFR_MANT(x);
! 82: yp = MPFR_MANT(y);
! 83: MPFR_EXP(y) = MPFR_EXP(x);
! 84:
! 85: dif = yn + 1 - xn;
1.1 maekawa 86:
87: /* we need to store yn+1 = xn + dif limbs of the quotient */
1.1.1.2 ! ohara 88: /* don't use tmp=yp since the mpn_lshift call below requires yp >= tmp+1 */
! 89: tmp = TMP_ALLOC((yn + 1) * BYTES_PER_MP_LIMB);
1.1 maekawa 90:
91: c = (mp_limb_t) u;
1.1.1.2 ! ohara 92: if (dif >= 0)
! 93: c = mpn_divrem_1 (tmp, dif, xp, xn, c); /* used all the dividend */
! 94: else /* dif < 0 i.e. xn > yn, don't use the (-dif) low limbs from x */
! 95: c = mpn_divrem_1 (tmp, 0, xp - dif, yn + 1, c);
! 96:
! 97: inexact = (c != 0);
! 98: if (rnd_mode == GMP_RNDN)
! 99: {
! 100: if (2 * c < (mp_limb_t) u)
! 101: middle = -1;
! 102: else if (2 * c > (mp_limb_t) u)
! 103: middle = 1;
! 104: else
! 105: middle = 0; /* exactly in the middle */
! 106: }
! 107: for (i=0; ((inexact == 0) || (middle == 0)) && (i < -dif); i++)
! 108: if (xp[i])
! 109: inexact = middle = 1; /* larger than middle */
! 110:
! 111: if (tmp[yn] == 0) /* high limb is zero */
! 112: {
! 113: tmp--;
! 114: sh = 0;
! 115: MPFR_EXP(y) -= BITS_PER_MP_LIMB;
! 116: }
! 117:
! 118: /* now we have yn limbs starting from tmp[1], with tmp[yn]<>0 */
1.1 maekawa 119:
120: /* shift left to normalize */
121: count_leading_zeros(sh, tmp[yn]);
1.1.1.2 ! ohara 122: if (sh)
! 123: {
! 124: mpn_lshift (yp, tmp + 1, yn, sh);
! 125: yp[0] += tmp[0] >> (BITS_PER_MP_LIMB - sh);
! 126: middle = middle || ((tmp[0] << sh) != 0);
! 127: inexact = inexact || ((tmp[0] << sh) != 0);
! 128: MPFR_EXP(y) -= sh;
! 129: }
! 130: else
! 131: MPN_COPY(yp, tmp + 1, yn);
1.1 maekawa 132:
1.1.1.2 ! ohara 133: sh = yn * BITS_PER_MP_LIMB - MPFR_PREC(y);
1.1 maekawa 134: /* it remains sh bits in less significant limb of y */
135:
1.1.1.2 ! ohara 136: d = *yp & ((MP_LIMB_T_ONE << sh) - MP_LIMB_T_ONE);
1.1 maekawa 137: *yp ^= d; /* set to zero lowest sh bits */
138:
139: TMP_FREE(marker);
1.1.1.2 ! ohara 140: if ((d == 0) && (inexact == 0))
! 141: return 0; /* result is exact */
! 142:
! 143: switch (rnd_mode)
! 144: {
! 145: case GMP_RNDZ:
! 146: MPFR_RET(-MPFR_SIGN(x)); /* result is inexact */
! 147:
! 148: case GMP_RNDU:
! 149: if (MPFR_SIGN(y) > 0)
! 150: mpfr_add_one_ulp (y, rnd_mode);
! 151: MPFR_RET(1); /* result is inexact */
! 152:
! 153: case GMP_RNDD:
! 154: if (MPFR_SIGN(y) < 0)
! 155: mpfr_add_one_ulp (y, rnd_mode);
! 156: MPFR_RET(-1); /* result is inexact */
! 157:
! 158: case GMP_RNDN:
! 159: if (sh && d < (MP_LIMB_T_ONE << (sh - 1)))
! 160: MPFR_RET(-MPFR_SIGN(x));
! 161: else if (sh && d > (MP_LIMB_T_ONE << (sh - 1)))
! 162: {
! 163: mpfr_add_one_ulp (y, rnd_mode);
! 164: MPFR_RET(MPFR_SIGN(x));
1.1 maekawa 165: }
1.1.1.2 ! ohara 166: else /* sh = 0 or d = 1 << (sh-1) */
! 167: {
! 168: /* we are in the middle if:
! 169: (a) sh > 0 and inexact == 0
! 170: (b) sh=0 and middle=1
! 171: */
! 172: if ((sh && inexact) || (!sh && (middle > 0)) || (*yp & (MP_LIMB_T_ONE << sh)))
! 173: {
! 174: mpfr_add_one_ulp (y, rnd_mode);
! 175: MPFR_RET(MPFR_SIGN(x));
! 176: }
! 177: else
! 178: MPFR_RET(-MPFR_SIGN(x));
1.1 maekawa 179: }
180: }
1.1.1.2 ! ohara 181: MPFR_RET(inexact); /* should never go here */
1.1 maekawa 182: }
183:
184:
185:
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