mirror of https://github.com/macssh/macssh.git
132 lines
4.3 KiB
C
Executable File
132 lines
4.3 KiB
C
Executable File
/* mpfr_pi -- compute Pi
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Copyright (C) 1999 PolKA project, Inria Lorraine and Loria
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This file is part of the MPFR Library.
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The MPFR Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Library General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at your
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option) any later version.
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The MPFR Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
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License for more details.
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You should have received a copy of the GNU Library General Public License
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along with the MPFR Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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#include <stdio.h>
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#include <math.h>
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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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#include "mpfr.h"
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/*
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Set x to the value of Pi to precision PREC(x) rounded to direction rnd_mode.
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Use the formula giving the binary representation of Pi found by Simon Plouffe
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and the Borwein's brothers:
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infinity 4 2 1 1
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----- ------- - ------- - ------- - -------
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\ 8 n + 1 8 n + 4 8 n + 5 8 n + 6
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Pi = ) -------------------------------------
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/ n
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----- 16
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n = 0
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i.e. Pi*16^N = S(N) + R(N) where
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S(N) = sum(16^(N-n)*(4/(8*n+1)-2/(8*n+4)-1/(8*n+5)-1/(8*n+6)), n=0..N-1)
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R(N) = sum((4/(8*n+1)-2/(8*n+4)-1/(8*n+5)-1/(8*n+6))/16^(n-N), n=N..infinity)
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Let f(n) = 4/(8*n+1)-2/(8*n+4)-1/(8*n+5)-1/(8*n+6), we can show easily that
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f(n) < 15/(64*n^2), so R(N) < sum(15/(64*n^2)/16^(n-N), n=N..infinity)
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< 15/64/N^2*sum(1/16^(n-N), n=N..infinity)
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= 1/4/N^2
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Now let S'(N) = sum(floor(16^(N-n)*(120*n^2+151*n+47),
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(512*n^4+1024*n^3+712*n^2+194*n+15)), n=0..N-1)
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S(N)-S'(N) <= sum(1, n=0..N-1) = N
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so Pi*16^N-S'(N) <= N+1 (as 1/4/N^2 < 1)
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*/
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mpfr_t __mpfr_pi; /* stored value of Pi */
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int __mpfr_pi_prec=0; /* precision of stored value */
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char __mpfr_pi_rnd; /* rounding mode of stored value */
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void
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#if __STDC__
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mpfr_pi(mpfr_ptr x, unsigned char rnd_mode)
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#else
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mpfr_pi(x, rnd_mode)
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mpfr_ptr x;
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unsigned char rnd_mode;
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#endif
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{
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int N, oldN, n, prec; mpz_t pi, num, den, d3, d2, tmp; mpfr_t y;
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prec=PREC(x);
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/* has stored value enough precision ? */
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if ((prec==__mpfr_pi_prec && rnd_mode==__mpfr_pi_rnd) ||
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(prec<=__mpfr_pi_prec &&
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mpfr_can_round(__mpfr_pi, __mpfr_pi_prec, __mpfr_pi_rnd, rnd_mode, prec)))
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{
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mpfr_set(x, __mpfr_pi, rnd_mode); return;
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}
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/* need to recompute */
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N=1;
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do {
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oldN = N;
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N = (prec+3)/4 + (int)ceil(log((double)N+1.0)/log(2.0));
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} while (N != oldN);
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mpz_init(pi); mpz_init(num); mpz_init(den); mpz_init(d3); mpz_init(d2);
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mpz_init(tmp);
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mpz_set_ui(pi, 0);
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mpz_set_ui(num, 16); /* num(-1) */
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mpz_set_ui(den, 21); /* den(-1) */
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mpz_set_si(d3, -2454);
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mpz_set_ui(d2, 14736);
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/* invariants: num=120*n^2+151*n+47, den=512*n^4+1024*n^3+712*n^2+194*n+15
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d3 = 2048*n^3+400*n-6, d2 = 6144*n^2-6144*n+2448
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*/
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for (n=0; n<N; n++) {
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/* num(n)-num(n-1) = 240*n+31 */
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mpz_add_ui(num, num, 240*n+31); /* no overflow up to PREC=71M */
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/* d2(n) - d2(n-1) = 12288*(n-1) */
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if (n>0) mpz_add_ui(d2, d2, 12288*(n-1));
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else mpz_sub_ui(d2, d2, 12288);
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/* d3(n) - d3(n-1) = d2 */
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mpz_add(d3, d3, d2);
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/* den(n)-den(n-1) = 2048*n^3 + 400n - 6 = d3 */
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mpz_add(den, den, d3);
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mpz_mul_2exp(tmp, num, 4*(N-n));
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mpz_fdiv_q(tmp, tmp, den);
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mpz_add(pi, pi, tmp);
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}
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mpfr_set_z(x, pi, rnd_mode);
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mpfr_init2(y, mpfr_get_prec(x));
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mpz_add_ui(pi, pi, N+1);
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mpfr_set_z(y, pi, rnd_mode);
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if (mpfr_cmp(x, y) != 0) {
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fprintf(stderr, "does not converge\n"); exit(1);
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}
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EXP(x) -= 4*N;
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mpz_clear(pi); mpz_clear(num); mpz_clear(den); mpz_clear(d3); mpz_clear(d2);
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mpz_clear(tmp); mpfr_clear(y);
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/* store computed value */
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if (__mpfr_pi_prec==0) mpfr_init2(__mpfr_pi, prec);
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else mpfr_set_prec(__mpfr_pi, prec);
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mpfr_set(__mpfr_pi, x, rnd_mode);
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__mpfr_pi_prec=prec;
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__mpfr_pi_rnd=rnd_mode;
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}
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