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Diffstat (limited to 'rts/gmp/mpn/generic/divrem_2.c')
| -rw-r--r-- | rts/gmp/mpn/generic/divrem_2.c | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/rts/gmp/mpn/generic/divrem_2.c b/rts/gmp/mpn/generic/divrem_2.c new file mode 100644 index 0000000000..0bc31ae2e7 --- /dev/null +++ b/rts/gmp/mpn/generic/divrem_2.c @@ -0,0 +1,151 @@ +/* mpn_divrem_2 -- Divide natural numbers, producing both remainder and + quotient. The divisor is two limbs. + + THIS FILE CONTAINS INTERNAL FUNCTIONS WITH MUTABLE INTERFACES. IT IS + ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES. IN FACT, IT IS + ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP + RELEASE. + + +Copyright (C) 1993, 1994, 1995, 1996, 1999, 2000 Free Software Foundation, +Inc. + +This file is part of the GNU MP Library. + +The GNU MP Library 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 GNU MP 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.LIB. If not, write to +the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, +MA 02111-1307, USA. */ + +#include "gmp.h" +#include "gmp-impl.h" +#include "longlong.h" + +/* Divide num (NP/NSIZE) by den (DP/2) and write + the NSIZE-2 least significant quotient limbs at QP + and the 2 long remainder at NP. If QEXTRA_LIMBS is + non-zero, generate that many fraction bits and append them after the + other quotient limbs. + Return the most significant limb of the quotient, this is always 0 or 1. + + Preconditions: + 0. NSIZE >= 2. + 1. The most significant bit of the divisor must be set. + 2. QP must either not overlap with the input operands at all, or + QP + 2 >= NP must hold true. (This means that it's + possible to put the quotient in the high part of NUM, right after the + remainder in NUM. + 3. NSIZE >= 2, even if QEXTRA_LIMBS is non-zero. */ + +mp_limb_t +#if __STDC__ +mpn_divrem_2 (mp_ptr qp, mp_size_t qxn, + mp_ptr np, mp_size_t nsize, + mp_srcptr dp) +#else +mpn_divrem_2 (qp, qxn, np, nsize, dp) + mp_ptr qp; + mp_size_t qxn; + mp_ptr np; + mp_size_t nsize; + mp_srcptr dp; +#endif +{ + mp_limb_t most_significant_q_limb = 0; + mp_size_t i; + mp_limb_t n1, n0, n2; + mp_limb_t d1, d0; + mp_limb_t d1inv; + int have_preinv; + + np += nsize - 2; + d1 = dp[1]; + d0 = dp[0]; + n1 = np[1]; + n0 = np[0]; + + if (n1 >= d1 && (n1 > d1 || n0 >= d0)) + { + sub_ddmmss (n1, n0, n1, n0, d1, d0); + most_significant_q_limb = 1; + } + + /* If multiplication is much faster than division, preinvert the most + significant divisor limb before entering the loop. */ + if (UDIV_TIME > 2 * UMUL_TIME + 6) + { + have_preinv = 0; + if ((UDIV_TIME - (2 * UMUL_TIME + 6)) * (nsize - 2) > UDIV_TIME) + { + invert_limb (d1inv, d1); + have_preinv = 1; + } + } + + for (i = qxn + nsize - 2 - 1; i >= 0; i--) + { + mp_limb_t q; + mp_limb_t r; + + if (i >= qxn) + np--; + else + np[0] = 0; + + if (n1 == d1) + { + /* Q should be either 111..111 or 111..110. Need special treatment + of this rare case as normal division would give overflow. */ + q = ~(mp_limb_t) 0; + + r = n0 + d1; + if (r < d1) /* Carry in the addition? */ + { + add_ssaaaa (n1, n0, r - d0, np[0], 0, d0); + qp[i] = q; + continue; + } + n1 = d0 - (d0 != 0); + n0 = -d0; + } + else + { + if (UDIV_TIME > 2 * UMUL_TIME + 6 && have_preinv) + udiv_qrnnd_preinv (q, r, n1, n0, d1, d1inv); + else + udiv_qrnnd (q, r, n1, n0, d1); + umul_ppmm (n1, n0, d0, q); + } + + n2 = np[0]; + + q_test: + if (n1 > r || (n1 == r && n0 > n2)) + { + /* The estimated Q was too large. */ + q--; + + sub_ddmmss (n1, n0, n1, n0, 0, d0); + r += d1; + if (r >= d1) /* If not carry, test Q again. */ + goto q_test; + } + + qp[i] = q; + sub_ddmmss (n1, n0, r, n2, n1, n0); + } + np[1] = n1; + np[0] = n0; + + return most_significant_q_limb; +} |