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* Copyright (C) 1999 - 2007 Michael C. Ring
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* Permission to use, copy, and distribute this software and its
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* documentation for any purpose with or without fee is hereby granted,
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* provided that the above copyright notice appear in all copies and
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* that both that copyright notice and this permission notice appear
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* in supporting documentation.
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* Permission to modify the software is granted. Permission to distribute
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* the modified code is granted. Modifications are to be distributed by
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* using the file 'license.txt' as a template to modify the file header.
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* 'license.txt' is available in the official MAPM distribution.
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* This software is provided "as is" without express or implied warranty.
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* This file contains the EXP function.
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#include "pgscript/utilities/mapm-lib/m_apm_lc.h"
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static M_APM MM_exp_log2R;
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static M_APM MM_exp_512R;
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static int MM_firsttime1 = TRUE;
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/****************************************************************************/
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if (MM_firsttime1 == FALSE)
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m_apm_free(MM_exp_log2R);
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m_apm_free(MM_exp_512R);
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/****************************************************************************/
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void m_apm_exp(M_APM r, int places, M_APM x)
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M_APM tmp7, tmp8, tmp9;
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MM_firsttime1 = FALSE;
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MM_exp_log2R = m_apm_init();
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MM_exp_512R = m_apm_init();
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m_apm_set_string(MM_exp_log2R, "1.44269504089"); /* ~ 1 / log(2) */
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m_apm_set_string(MM_exp_512R, "1.953125E-3"); /* 1 / 512 */
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tmp7 = M_get_stack_var();
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tmp8 = M_get_stack_var();
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tmp9 = M_get_stack_var();
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if (x->m_apm_sign == 0) /* if input == 0, return '1' */
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m_apm_copy(r, MM_One);
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if (x->m_apm_exponent <= -3) /* already small enough so call _raw directly */
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M_raw_exp(tmp9, (places + 6), x);
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m_apm_round(r, places, tmp9);
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From David H. Bailey's MPFUN Fortran package :
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exp (t) = (1 + r + r^2 / 2! + r^3 / 3! + r^4 / 4! ...) ^ q * 2 ^ n
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where q = 256, r = t' / q, t' = t - n Log(2) and where n is chosen so
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that -0.5 Log(2) < t' <= 0.5 Log(2). Reducing t mod Log(2) and
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dividing by 256 insures that -0.001 < r <= 0.001, which accelerates
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convergence in the above series.
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I use q = 512 and also limit how small 'r' can become. The 'r' used
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here is limited in magnitude from 1.95E-4 < |r| < 1.35E-3. Forcing
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'r' into a narrow range keeps the algorithm 'well behaved'.
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( the range is [0.1 / 512] to [log(2) / 512] )
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if (M_exp_compute_nn(&nn, tmp7, x) != 0)
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M_apm_log_error_msg(M_APM_RETURN,
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"\'m_apm_exp\', Input too large, Overflow");
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dplaces = places + 8;
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/* check to make sure our log(2) is accurate enough */
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M_check_log_places(dplaces);
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m_apm_multiply(tmp8, tmp7, MM_lc_log2);
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m_apm_subtract(tmp7, x, tmp8);
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* guarantee that |tmp7| is between 0.1 and 0.9999999....
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* (in practice, the upper limit only reaches log(2), 0.693... )
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if (tmp7->m_apm_sign != 0)
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if (tmp7->m_apm_exponent == 0)
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if (tmp7->m_apm_sign >= 0)
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m_apm_subtract(tmp8, tmp7, MM_lc_log2);
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m_apm_copy(tmp7, tmp8);
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m_apm_add(tmp8, tmp7, MM_lc_log2);
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m_apm_copy(tmp7, tmp8);
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m_apm_multiply(tmp9, tmp7, MM_exp_512R);
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/* perform the series expansion ... */
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M_raw_exp(tmp8, dplaces, tmp9);
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* raise result to the 512 power
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* note : x ^ 512 = (((x ^ 2) ^ 2) ^ 2) ... 9 times
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m_apm_multiply(tmp9, tmp8, tmp8);
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m_apm_round(tmp8, dplaces, tmp9);
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/* now compute 2 ^ N */
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m_apm_integer_pow(tmp7, dplaces, MM_Two, nn);
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m_apm_multiply(tmp9, tmp7, tmp8);
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m_apm_round(r, places, tmp9);
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M_restore_stack(3); /* restore the 3 locals we used here */
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/****************************************************************************/
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compute int *n = round_to_nearest_int(a / log(2))
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M_APM b = MAPM version of *n
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int M_exp_compute_nn(int *n, M_APM b, M_APM a)
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tmp0 = M_get_stack_var();
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tmp1 = M_get_stack_var();
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/* find 'n' and convert it to a normal C int */
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/* we just need an approx 1/log(2) for this calculation */
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m_apm_multiply(tmp1, a, MM_exp_log2R);
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/* round to the nearest int */
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if (tmp1->m_apm_sign >= 0)
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m_apm_add(tmp0, tmp1, MM_0_5);
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m_apm_floor(tmp1, tmp0);
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m_apm_subtract(tmp0, tmp1, MM_0_5);
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m_apm_ceil(tmp1, tmp0);
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kk = tmp1->m_apm_exponent;
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if ((vp = (void *)MAPM_MALLOC((kk + 16) * sizeof(char))) == NULL)
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/* fatal, this does not return */
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M_apm_log_error_msg(M_APM_FATAL, "\'M_exp_compute_nn\', Out of memory");
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m_apm_to_integer_string(cp, tmp1);
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m_apm_set_long(b, (long)(*n));
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kk = m_apm_compare(b, tmp1);
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/****************************************************************************/
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calculate the exponential function using the following series :
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exp(x) == 1 + x + --- + --- + --- + --- ...
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void M_raw_exp(M_APM rr, int places, M_APM xx)
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M_APM tmp0, digit, term;
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int tolerance, local_precision, prev_exp;
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tmp0 = M_get_stack_var();
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term = M_get_stack_var();
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digit = M_get_stack_var();
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local_precision = places + 8;
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tolerance = -(places + 4);
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m_apm_add(rr, MM_One, xx);
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m_apm_copy(term, xx);
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m_apm_set_long(digit, m1);
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m_apm_multiply(tmp0, term, xx);
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m_apm_divide(term, local_precision, tmp0, digit);
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m_apm_add(tmp0, rr, term);
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m_apm_copy(rr, tmp0);
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if ((term->m_apm_exponent < tolerance) || (term->m_apm_sign == 0))
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local_precision = local_precision + term->m_apm_exponent - prev_exp;
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if (local_precision < 20)
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local_precision = 20;
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prev_exp = term->m_apm_exponent;
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M_restore_stack(3); /* restore the 3 locals we used here */
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/****************************************************************************/