| /* mpn_divmod_1(quot_ptr, dividend_ptr, dividend_size, divisor_limb) -- |
| Divide (DIVIDEND_PTR,,DIVIDEND_SIZE) by DIVISOR_LIMB. |
| Write DIVIDEND_SIZE limbs of quotient at QUOT_PTR. |
| Return the single-limb remainder. |
| There are no constraints on the value of the divisor. |
| |
| QUOT_PTR and DIVIDEND_PTR might point to the same limb. |
| |
| Copyright (C) 1991-2018 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, see |
| <http://www.gnu.org/licenses/>. */ |
| |
| #include <gmp.h> |
| #include "gmp-impl.h" |
| #include "longlong.h" |
| |
| #ifndef UMUL_TIME |
| #define UMUL_TIME 1 |
| #endif |
| |
| #ifndef UDIV_TIME |
| #define UDIV_TIME UMUL_TIME |
| #endif |
| |
| /* FIXME: We should be using invert_limb (or invert_normalized_limb) |
| here (not udiv_qrnnd). */ |
| |
| mp_limb_t |
| mpn_divmod_1 (mp_ptr quot_ptr, |
| mp_srcptr dividend_ptr, mp_size_t dividend_size, |
| mp_limb_t divisor_limb) |
| { |
| mp_size_t i; |
| mp_limb_t n1, n0, r; |
| mp_limb_t dummy __attribute__ ((unused)); |
| |
| /* ??? Should this be handled at all? Rely on callers? */ |
| if (dividend_size == 0) |
| return 0; |
| |
| /* If multiplication is much faster than division, and the |
| dividend is large, pre-invert the divisor, and use |
| only multiplications in the inner loop. */ |
| |
| /* This test should be read: |
| Does it ever help to use udiv_qrnnd_preinv? |
| && Does what we save compensate for the inversion overhead? */ |
| if (UDIV_TIME > (2 * UMUL_TIME + 6) |
| && (UDIV_TIME - (2 * UMUL_TIME + 6)) * dividend_size > UDIV_TIME) |
| { |
| int normalization_steps; |
| |
| count_leading_zeros (normalization_steps, divisor_limb); |
| if (normalization_steps != 0) |
| { |
| mp_limb_t divisor_limb_inverted; |
| |
| divisor_limb <<= normalization_steps; |
| |
| /* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB. The |
| result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the |
| most significant bit (with weight 2**N) implicit. */ |
| |
| /* Special case for DIVISOR_LIMB == 100...000. */ |
| if (divisor_limb << 1 == 0) |
| divisor_limb_inverted = ~(mp_limb_t) 0; |
| else |
| udiv_qrnnd (divisor_limb_inverted, dummy, |
| -divisor_limb, 0, divisor_limb); |
| |
| n1 = dividend_ptr[dividend_size - 1]; |
| r = n1 >> (BITS_PER_MP_LIMB - normalization_steps); |
| |
| /* Possible optimization: |
| if (r == 0 |
| && divisor_limb > ((n1 << normalization_steps) |
| | (dividend_ptr[dividend_size - 2] >> ...))) |
| ...one division less... */ |
| |
| for (i = dividend_size - 2; i >= 0; i--) |
| { |
| n0 = dividend_ptr[i]; |
| udiv_qrnnd_preinv (quot_ptr[i + 1], r, r, |
| ((n1 << normalization_steps) |
| | (n0 >> (BITS_PER_MP_LIMB - normalization_steps))), |
| divisor_limb, divisor_limb_inverted); |
| n1 = n0; |
| } |
| udiv_qrnnd_preinv (quot_ptr[0], r, r, |
| n1 << normalization_steps, |
| divisor_limb, divisor_limb_inverted); |
| return r >> normalization_steps; |
| } |
| else |
| { |
| mp_limb_t divisor_limb_inverted; |
| |
| /* Compute (2**2N - 2**N * DIVISOR_LIMB) / DIVISOR_LIMB. The |
| result is a (N+1)-bit approximation to 1/DIVISOR_LIMB, with the |
| most significant bit (with weight 2**N) implicit. */ |
| |
| /* Special case for DIVISOR_LIMB == 100...000. */ |
| if (divisor_limb << 1 == 0) |
| divisor_limb_inverted = ~(mp_limb_t) 0; |
| else |
| udiv_qrnnd (divisor_limb_inverted, dummy, |
| -divisor_limb, 0, divisor_limb); |
| |
| i = dividend_size - 1; |
| r = dividend_ptr[i]; |
| |
| if (r >= divisor_limb) |
| r = 0; |
| else |
| { |
| quot_ptr[i] = 0; |
| i--; |
| } |
| |
| for (; i >= 0; i--) |
| { |
| n0 = dividend_ptr[i]; |
| udiv_qrnnd_preinv (quot_ptr[i], r, r, |
| n0, divisor_limb, divisor_limb_inverted); |
| } |
| return r; |
| } |
| } |
| else |
| { |
| if (UDIV_NEEDS_NORMALIZATION) |
| { |
| int normalization_steps; |
| |
| count_leading_zeros (normalization_steps, divisor_limb); |
| if (normalization_steps != 0) |
| { |
| divisor_limb <<= normalization_steps; |
| |
| n1 = dividend_ptr[dividend_size - 1]; |
| r = n1 >> (BITS_PER_MP_LIMB - normalization_steps); |
| |
| /* Possible optimization: |
| if (r == 0 |
| && divisor_limb > ((n1 << normalization_steps) |
| | (dividend_ptr[dividend_size - 2] >> ...))) |
| ...one division less... */ |
| |
| for (i = dividend_size - 2; i >= 0; i--) |
| { |
| n0 = dividend_ptr[i]; |
| udiv_qrnnd (quot_ptr[i + 1], r, r, |
| ((n1 << normalization_steps) |
| | (n0 >> (BITS_PER_MP_LIMB - normalization_steps))), |
| divisor_limb); |
| n1 = n0; |
| } |
| udiv_qrnnd (quot_ptr[0], r, r, |
| n1 << normalization_steps, |
| divisor_limb); |
| return r >> normalization_steps; |
| } |
| } |
| /* No normalization needed, either because udiv_qrnnd doesn't require |
| it, or because DIVISOR_LIMB is already normalized. */ |
| |
| i = dividend_size - 1; |
| r = dividend_ptr[i]; |
| |
| if (r >= divisor_limb) |
| r = 0; |
| else |
| { |
| quot_ptr[i] = 0; |
| i--; |
| } |
| |
| for (; i >= 0; i--) |
| { |
| n0 = dividend_ptr[i]; |
| udiv_qrnnd (quot_ptr[i], r, r, n0, divisor_limb); |
| } |
| return r; |
| } |
| } |