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Diffstat (limited to 'stdlib/divrem.c')
| -rw-r--r-- | stdlib/divrem.c | 245 |
1 files changed, 245 insertions, 0 deletions
diff --git a/stdlib/divrem.c b/stdlib/divrem.c new file mode 100644 index 0000000000..c97d01ec17 --- /dev/null +++ b/stdlib/divrem.c @@ -0,0 +1,245 @@ +/* mpn_divrem -- Divide natural numbers, producing both remainder and + quotient. + +Copyright (C) 1993, 1994, 1995, 1996 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/DSIZE) and write + the NSIZE-DSIZE least significant quotient limbs at QP + and the DSIZE 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 >= DSIZE. + 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 + DSIZE >= 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 >= DSIZE, even if QEXTRA_LIMBS is non-zero. */ + +mp_limb_t +#if __STDC__ +mpn_divrem (mp_ptr qp, mp_size_t qextra_limbs, + mp_ptr np, mp_size_t nsize, + mp_srcptr dp, mp_size_t dsize) +#else +mpn_divrem (qp, qextra_limbs, np, nsize, dp, dsize) + mp_ptr qp; + mp_size_t qextra_limbs; + mp_ptr np; + mp_size_t nsize; + mp_srcptr dp; + mp_size_t dsize; +#endif +{ + mp_limb_t most_significant_q_limb = 0; + + switch (dsize) + { + case 0: + /* We are asked to divide by zero, so go ahead and do it! (To make + the compiler not remove this statement, return the value.) */ + return 1 / dsize; + + case 1: + { + mp_size_t i; + mp_limb_t n1; + mp_limb_t d; + + d = dp[0]; + n1 = np[nsize - 1]; + + if (n1 >= d) + { + n1 -= d; + most_significant_q_limb = 1; + } + + qp += qextra_limbs; + for (i = nsize - 2; i >= 0; i--) + udiv_qrnnd (qp[i], n1, n1, np[i], d); + qp -= qextra_limbs; + + for (i = qextra_limbs - 1; i >= 0; i--) + udiv_qrnnd (qp[i], n1, n1, 0, d); + + np[0] = n1; + } + break; + + case 2: + { + mp_size_t i; + mp_limb_t n1, n0, n2; + mp_limb_t d1, d0; + + 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; + } + + for (i = qextra_limbs + nsize - 2 - 1; i >= 0; i--) + { + mp_limb_t q; + mp_limb_t r; + + if (i >= qextra_limbs) + 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 + { + 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; + } + break; + + default: + { + mp_size_t i; + mp_limb_t dX, d1, n0; + + np += nsize - dsize; + dX = dp[dsize - 1]; + d1 = dp[dsize - 2]; + n0 = np[dsize - 1]; + + if (n0 >= dX) + { + if (n0 > dX || mpn_cmp (np, dp, dsize - 1) >= 0) + { + mpn_sub_n (np, np, dp, dsize); + n0 = np[dsize - 1]; + most_significant_q_limb = 1; + } + } + + for (i = qextra_limbs + nsize - dsize - 1; i >= 0; i--) + { + mp_limb_t q; + mp_limb_t n1, n2; + mp_limb_t cy_limb; + + if (i >= qextra_limbs) + { + np--; + n2 = np[dsize]; + } + else + { + n2 = np[dsize - 1]; + MPN_COPY_DECR (np + 1, np, dsize); + np[0] = 0; + } + + if (n0 == dX) + /* This might over-estimate q, but it's probably not worth + the extra code here to find out. */ + q = ~(mp_limb_t) 0; + else + { + mp_limb_t r; + + udiv_qrnnd (q, r, n0, np[dsize - 1], dX); + umul_ppmm (n1, n0, d1, q); + + while (n1 > r || (n1 == r && n0 > np[dsize - 2])) + { + q--; + r += dX; + if (r < dX) /* I.e. "carry in previous addition?" */ + break; + n1 -= n0 < d1; + n0 -= d1; + } + } + + /* Possible optimization: We already have (q * n0) and (1 * n1) + after the calculation of q. Taking advantage of that, we + could make this loop make two iterations less. */ + + cy_limb = mpn_submul_1 (np, dp, dsize, q); + + if (n2 != cy_limb) + { + mpn_add_n (np, np, dp, dsize); + q--; + } + + qp[i] = q; + n0 = np[dsize - 1]; + } + } + } + + return most_significant_q_limb; +} |