/* mpfr_const_pi -- compute Pi Copyright 1999, 2000, 2001 Free Software Foundation. This file is part of the MPFR Library. The MPFR 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 MPFR 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 MPFR 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 #include #include "gmp.h" #include "gmp-impl.h" #include "longlong.h" #include "mpfr.h" #include "mpfr-impl.h" static int mpfr_aux_pi _PROTO ((mpfr_ptr, mpz_srcptr, int, int)); static int mpfr_pi_machin3 _PROTO ((mpfr_ptr, mp_rnd_t)); #define A #define A1 1 #define A2 2 #undef B #define C #define C1 3 #define C2 2 #define GENERIC mpfr_aux_pi #define R_IS_RATIONAL #define NO_FACTORIAL #include "generic.c" static int mpfr_pi_machin3 (mpfr_ptr mylog, mp_rnd_t rnd_mode) { int prec, logn, prec_x; int prec_i_want=MPFR_PREC(mylog); int good = 0; mpfr_t tmp1, tmp2, result,tmp3,tmp4,tmp5,tmp6; mpz_t cst; MPFR_CLEAR_FLAGS(mylog); logn = _mpfr_ceil_log2 ((double) MPFR_PREC(mylog)); prec_x = prec_i_want + logn + 5; mpz_init(cst); while (!good){ prec = _mpfr_ceil_log2 ((double) prec_x); mpfr_init2(tmp1, prec_x); mpfr_init2(tmp2, prec_x); mpfr_init2(tmp3, prec_x); mpfr_init2(tmp4, prec_x); mpfr_init2(tmp5, prec_x); mpfr_init2(tmp6, prec_x); mpfr_init2(result, prec_x); mpz_set_si(cst, -1); mpfr_aux_pi(tmp1, cst, 268*268, prec - 4); mpfr_div_ui(tmp1, tmp1, 268, GMP_RNDD); mpfr_mul_ui(tmp1, tmp1, 61, GMP_RNDD); mpfr_aux_pi(tmp2, cst, 343*343, prec - 4); mpfr_div_ui(tmp2, tmp2, 343, GMP_RNDD); mpfr_mul_ui(tmp2, tmp2, 122, GMP_RNDD); mpfr_aux_pi(tmp3, cst, 557*557, prec - 4); mpfr_div_ui(tmp3, tmp3, 557, GMP_RNDD); mpfr_mul_ui(tmp3, tmp3, 115, GMP_RNDD); mpfr_aux_pi(tmp4, cst, 1068*1068, prec - 4); mpfr_div_ui(tmp4, tmp4, 1068, GMP_RNDD); mpfr_mul_ui(tmp4, tmp4, 32, GMP_RNDD); mpfr_aux_pi(tmp5, cst, 3458*3458, prec - 4); mpfr_div_ui(tmp5, tmp5, 3458, GMP_RNDD); mpfr_mul_ui(tmp5, tmp5, 83, GMP_RNDD); mpfr_aux_pi(tmp6, cst, 27493*27493, prec - 4); mpfr_div_ui(tmp6, tmp6, 27493, GMP_RNDD); mpfr_mul_ui(tmp6, tmp6, 44, GMP_RNDD); mpfr_add(result, tmp1, tmp2, GMP_RNDD); mpfr_add(result, result, tmp3, GMP_RNDD); mpfr_sub(result, result, tmp4, GMP_RNDD); mpfr_add(result, result, tmp5, GMP_RNDD); mpfr_add(result, result, tmp6, GMP_RNDD); mpfr_mul_2ui(result, result, 2, GMP_RNDD); mpfr_clear(tmp1); mpfr_clear(tmp2); mpfr_clear(tmp3); mpfr_clear(tmp4); mpfr_clear(tmp5); mpfr_clear(tmp6); if (mpfr_can_round(result, prec_x - 5, GMP_RNDD, rnd_mode, prec_i_want)){ mpfr_set(mylog, result, rnd_mode); mpfr_clear(result); good = 1; } else { mpfr_clear(result); prec_x += logn; } } mpz_clear(cst); return 0; } /* Set x to the value of Pi to precision MPFR_PREC(x) rounded to direction rnd_mode. Use the formula giving the binary representation of Pi found by Simon Plouffe and the Borwein's brothers: infinity 4 2 1 1 ----- ------- - ------- - ------- - ------- \ 8 n + 1 8 n + 4 8 n + 5 8 n + 6 Pi = ) ------------------------------------- / n ----- 16 n = 0 i.e. Pi*16^N = S(N) + R(N) where 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) 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) Let f(n) = 4/(8*n+1)-2/(8*n+4)-1/(8*n+5)-1/(8*n+6), we can show easily that f(n) < 15/(64*n^2), so R(N) < sum(15/(64*n^2)/16^(n-N), n=N..infinity) < 15/64/N^2*sum(1/16^(n-N), n=N..infinity) = 1/4/N^2 Now let S'(N) = sum(floor(16^(N-n)*(120*n^2+151*n+47), (512*n^4+1024*n^3+712*n^2+194*n+15)), n=0..N-1) S(N)-S'(N) <= sum(1, n=0..N-1) = N so Pi*16^N-S'(N) <= N+1 (as 1/4/N^2 < 1) */ mpfr_t __mpfr_const_pi; /* stored value of Pi */ int __mpfr_const_pi_prec=0; /* precision of stored value */ mp_rnd_t __mpfr_const_pi_rnd; /* rounding mode of stored value */ void mpfr_const_pi (mpfr_ptr x, mp_rnd_t rnd_mode) { int N, oldN, n, prec; mpz_t pi, num, den, d3, d2, tmp; mpfr_t y; prec=MPFR_PREC(x); /* has stored value enough precision ? */ if ((prec==__mpfr_const_pi_prec && rnd_mode==__mpfr_const_pi_rnd) || (prec<=__mpfr_const_pi_prec && mpfr_can_round(__mpfr_const_pi, __mpfr_const_pi_prec, __mpfr_const_pi_rnd, rnd_mode, prec))) { mpfr_set(x, __mpfr_const_pi, rnd_mode); return; } if (prec < 20000){ /* need to recompute */ N=1; do { oldN = N; N = (prec+3)/4 + _mpfr_ceil_log2((double) N + 1.0); } while (N != oldN); mpz_init(pi); mpz_init(num); mpz_init(den); mpz_init(d3); mpz_init(d2); mpz_init(tmp); mpz_set_ui(pi, 0); mpz_set_ui(num, 16); /* num(-1) */ mpz_set_ui(den, 21); /* den(-1) */ mpz_set_si(d3, -2454); mpz_set_ui(d2, 14736); /* invariants: num=120*n^2+151*n+47, den=512*n^4+1024*n^3+712*n^2+194*n+15 d3 = 2048*n^3+400*n-6, d2 = 6144*n^2-6144*n+2448 */ for (n=0; n0) mpz_add_ui(d2, d2, 12288*(n-1)); else mpz_sub_ui(d2, d2, 12288); /* d3(n) - d3(n-1) = d2 */ mpz_add(d3, d3, d2); /* den(n)-den(n-1) = 2048*n^3 + 400n - 6 = d3 */ mpz_add(den, den, d3); mpz_mul_2exp(tmp, num, 4*(N-n)); mpz_fdiv_q(tmp, tmp, den); mpz_add(pi, pi, tmp); } mpfr_set_z(x, pi, rnd_mode); mpfr_init2(y, mpfr_get_prec(x)); mpz_add_ui(pi, pi, N+1); mpfr_set_z(y, pi, rnd_mode); if (mpfr_cmp(x, y) != 0) { fprintf(stderr, "does not converge\n"); exit(1); } MPFR_EXP(x) -= 4*N; mpz_clear(pi); mpz_clear(num); mpz_clear(den); mpz_clear(d3); mpz_clear(d2); mpz_clear(tmp); mpfr_clear(y); } else mpfr_pi_machin3(x, rnd_mode); /* store computed value */ if (__mpfr_const_pi_prec==0) mpfr_init2(__mpfr_const_pi, prec); else mpfr_set_prec(__mpfr_const_pi, prec); mpfr_set(__mpfr_const_pi, x, rnd_mode); __mpfr_const_pi_prec=prec; __mpfr_const_pi_rnd=rnd_mode; }