/* glplib05.c (bignum arithmetic) */ /*********************************************************************** * This code is part of GLPK (GNU Linear Programming Kit). * * Copyright (C) 2000, 01, 02, 03, 04, 05, 06, 07, 08 Andrew Makhorin, * Department for Applied Informatics, Moscow Aviation Institute, * Moscow, Russia. All rights reserved. E-mail: <mao@mai2.rcnet.ru>. * * GLPK is free software: you can redistribute it and/or modify it * under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * GLPK 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 General Public * License for more details. * * You should have received a copy of the GNU General Public License * along with GLPK. If not, see <http://www.gnu.org/licenses/>. ***********************************************************************/ #include "glplib.h" /*********************************************************************** * Two routines below are intended to multiply and divide unsigned * integer numbers of arbitrary precision. * * The routines assume that an unsigned integer number is represented in * the positional numeral system with the base 2^16 = 65536, i.e. each * "digit" of the number is in the range [0, 65535] and represented as * a 16-bit value of the unsigned short type. In other words, a number x * has the following representation: * * n-1 * x = sum d[j] * 65536^j, * j=0 * * where n is the number of places (positions), and d[j] is j-th "digit" * of x, 0 <= d[j] <= 65535. ***********************************************************************/ /*********************************************************************** * NAME * * bigmul - multiply unsigned integer numbers of arbitrary precision * * SYNOPSIS * * #include "glplib.h" * void bigmul(int n, int m, unsigned short x[], unsigned short y[]); * * DESCRIPTION * * The routine bigmul multiplies unsigned integer numbers of arbitrary * precision. * * n is the number of digits of multiplicand, n >= 1; * * m is the number of digits of multiplier, m >= 1; * * x is an array containing digits of the multiplicand in elements * x[m], x[m+1], ..., x[n+m-1]. Contents of x[0], x[1], ..., x[m-1] are * ignored on entry. * * y is an array containing digits of the multiplier in elements y[0], * y[1], ..., y[m-1]. * * On exit digits of the product are stored in elements x[0], x[1], ..., * x[n+m-1]. The array y is not changed. */ void bigmul(int n, int m, unsigned short x[], unsigned short y[]) { int i, j; unsigned int t; xassert(n >= 1); xassert(m >= 1); for (j = 0; j < m; j++) x[j] = 0; for (i = 0; i < n; i++) { if (x[i+m]) { t = 0; for (j = 0; j < m; j++) { t += (unsigned int)x[i+m] * (unsigned int)y[j] + (unsigned int)x[i+j]; x[i+j] = (unsigned short)t; t >>= 16; } x[i+m] = (unsigned short)t; } } return; } /*********************************************************************** * NAME * * bigdiv - divide unsigned integer numbers of arbitrary precision * * SYNOPSIS * * #include "glplib.h" * void bigdiv(int n, int m, unsigned short x[], unsigned short y[]); * * DESCRIPTION * * The routine bigdiv divides one unsigned integer number of arbitrary * precision by another with the algorithm described in [1]. * * n is the difference between the number of digits of dividend and the * number of digits of divisor, n >= 0. * * m is the number of digits of divisor, m >= 1. * * x is an array containing digits of the dividend in elements x[0], * x[1], ..., x[n+m-1]. * * y is an array containing digits of the divisor in elements y[0], * y[1], ..., y[m-1]. The highest digit y[m-1] must be non-zero. * * On exit n+1 digits of the quotient are stored in elements x[m], * x[m+1], ..., x[n+m], and m digits of the remainder are stored in * elements x[0], x[1], ..., x[m-1]. The array y is changed but then * restored. * * REFERENCES * * 1. D. Knuth. The Art of Computer Programming. Vol. 2: Seminumerical * Algorithms. Stanford University, 1969. */ void bigdiv(int n, int m, unsigned short x[], unsigned short y[]) { int i, j; unsigned int t; unsigned short d, q, r; xassert(n >= 0); xassert(m >= 1); xassert(y[m-1] != 0); /* special case when divisor has the only digit */ if (m == 1) { d = 0; for (i = n; i >= 0; i--) { t = ((unsigned int)d << 16) + (unsigned int)x[i]; x[i+1] = (unsigned short)(t / y[0]); d = (unsigned short)(t % y[0]); } x[0] = d; goto done; } /* multiply dividend and divisor by a normalizing coefficient in order to provide the condition y[m-1] >= base / 2 */ d = (unsigned short)(0x10000 / ((unsigned int)y[m-1] + 1)); if (d == 1) x[n+m] = 0; else { t = 0; for (i = 0; i < n+m; i++) { t += (unsigned int)x[i] * (unsigned int)d; x[i] = (unsigned short)t; t >>= 16; } x[n+m] = (unsigned short)t; t = 0; for (j = 0; j < m; j++) { t += (unsigned int)y[j] * (unsigned int)d; y[j] = (unsigned short)t; t >>= 16; } } /* main loop */ for (i = n; i >= 0; i--) { /* estimate and correct the current digit of quotient */ if (x[i+m] < y[m-1]) { t = ((unsigned int)x[i+m] << 16) + (unsigned int)x[i+m-1]; q = (unsigned short)(t / (unsigned int)y[m-1]); r = (unsigned short)(t % (unsigned int)y[m-1]); if (q == 0) goto putq; else goto test; } q = 0; r = x[i+m-1]; decr: q--; /* if q = 0 then q-- = 0xFFFF */ t = (unsigned int)r + (unsigned int)y[m-1]; r = (unsigned short)t; if (t > 0xFFFF) goto msub; test: t = (unsigned int)y[m-2] * (unsigned int)q; if ((unsigned short)(t >> 16) > r) goto decr; if ((unsigned short)(t >> 16) < r) goto msub; if ((unsigned short)t > x[i+m-2]) goto decr; msub: /* now subtract divisor multiplied by the current digit of quotient from the current dividend */ if (q == 0) goto putq; t = 0; for (j = 0; j < m; j++) { t += (unsigned int)y[j] * (unsigned int)q; if (x[i+j] < (unsigned short)t) t += 0x10000; x[i+j] -= (unsigned short)t; t >>= 16; } if (x[i+m] >= (unsigned short)t) goto putq; /* perform correcting addition, because the current digit of quotient is greater by one than its correct value */ q--; t = 0; for (j = 0; j < m; j++) { t += (unsigned int)x[i+j] + (unsigned int)y[j]; x[i+j] = (unsigned short)t; t >>= 16; } putq: /* store the current digit of quotient */ x[i+m] = q; } /* divide divisor and remainder by the normalizing coefficient in order to restore their original values */ if (d > 1) { t = 0; for (i = m-1; i >= 0; i--) { t = (t << 16) + (unsigned int)x[i]; x[i] = (unsigned short)(t / (unsigned int)d); t %= (unsigned int)d; } t = 0; for (j = m-1; j >= 0; j--) { t = (t << 16) + (unsigned int)y[j]; y[j] = (unsigned short)(t / (unsigned int)d); t %= (unsigned int)d; } } done: return; } /**********************************************************************/ #if 0 #include <assert.h> #include <stdio.h> #include <stdlib.h> #include "glprng.h" #define N_MAX 7 /* maximal number of digits in multiplicand */ #define M_MAX 5 /* maximal number of digits in multiplier */ #define N_TEST 1000000 /* number of tests */ int main(void) { RNG *rand; int d, j, n, m, test; unsigned short x[N_MAX], y[M_MAX], z[N_MAX+M_MAX]; rand = rng_create_rand(); for (test = 1; test <= N_TEST; test++) { /* x[0,...,n-1] := multiplicand */ n = 1 + rng_unif_rand(rand, N_MAX-1); assert(1 <= n && n <= N_MAX); for (j = 0; j < n; j++) { d = rng_unif_rand(rand, 65536); assert(0 <= d && d <= 65535); x[j] = (unsigned short)d; } /* y[0,...,m-1] := multiplier */ m = 1 + rng_unif_rand(rand, M_MAX-1); assert(1 <= m && m <= M_MAX); for (j = 0; j < m; j++) { d = rng_unif_rand(rand, 65536); assert(0 <= d && d <= 65535); y[j] = (unsigned short)d; } if (y[m-1] == 0) y[m-1] = 1; /* z[0,...,n+m-1] := x * y */ for (j = 0; j < n; j++) z[m+j] = x[j]; bigmul(n, m, z, y); /* z[0,...,m-1] := z mod y, z[m,...,n+m-1] := z div y */ bigdiv(n, m, z, y); /* z mod y must be 0 */ for (j = 0; j < m; j++) assert(z[j] == 0); /* z div y must be x */ for (j = 0; j < n; j++) assert(z[m+j] == x[j]); } fprintf(stderr, "%d tests successfully passed\n", N_TEST); rng_delete_rand(rand); return 0; } #endif /* eof */

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