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https://github.com/levinsv/pgadmin3.git
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129 lines
3 KiB
C++
129 lines
3 KiB
C++
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/*
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* M_APM - mapmcbrt.c
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*
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* Copyright (C) 2000 - 2007 Michael C. Ring
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*
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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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*
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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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*
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* This software is provided "as is" without express or implied warranty.
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*/
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/*
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*
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* This file contains the CBRT (cube root) function.
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*
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*/
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#include "pgAdmin3.h"
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#include "pgscript/utilities/mapm-lib/m_apm_lc.h"
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/****************************************************************************/
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void m_apm_cbrt(M_APM rr, int places, M_APM aa)
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{
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M_APM last_x, guess, tmpN, tmp7, tmp8, tmp9;
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int ii, nexp, bflag, tolerance, maxp, local_precision;
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/* result is 0 if input is 0 */
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if (aa->m_apm_sign == 0)
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{
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M_set_to_zero(rr);
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return;
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}
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last_x = M_get_stack_var();
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guess = M_get_stack_var();
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tmpN = M_get_stack_var();
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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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/* compute the cube root of the positive number, we'll fix the sign later */
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m_apm_absolute_value(tmpN, aa);
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/*
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normalize the input number (make the exponent near 0) so
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the 'guess' function will not over/under flow on large
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magnitude exponents.
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*/
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nexp = aa->m_apm_exponent / 3;
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tmpN->m_apm_exponent -= 3 * nexp;
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M_get_cbrt_guess(guess, tmpN);
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tolerance = places + 4;
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maxp = places + 16;
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bflag = FALSE;
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local_precision = 14;
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m_apm_negate(last_x, MM_Ten);
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/* Use the following iteration to calculate 1 / cbrt(N) :
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4
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X = [ 4 * X - N * X ] / 3
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n+1
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*/
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ii = 0;
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while (TRUE)
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{
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m_apm_multiply(tmp8, guess, guess);
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m_apm_multiply(tmp7, tmp8, tmp8);
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m_apm_round(tmp8, local_precision, tmp7);
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m_apm_multiply(tmp9, tmpN, tmp8);
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m_apm_multiply(tmp8, MM_Four, guess);
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m_apm_subtract(tmp7, tmp8, tmp9);
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m_apm_divide(guess, local_precision, tmp7, MM_Three);
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if (bflag)
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break;
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/* force at least 2 iterations so 'last_x' has valid data */
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if (ii != 0)
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{
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m_apm_subtract(tmp8, guess, last_x);
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if (tmp8->m_apm_sign == 0)
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break;
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if ((-4 * tmp8->m_apm_exponent) > tolerance)
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bflag = TRUE;
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}
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local_precision *= 2;
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if (local_precision > maxp)
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local_precision = maxp;
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m_apm_copy(last_x, guess);
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ii = 1;
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}
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/* final cbrt = N * guess ^ 2 */
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m_apm_multiply(tmp9, guess, guess);
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m_apm_multiply(tmp8, tmp9, tmpN);
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m_apm_round(rr, places, tmp8);
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rr->m_apm_exponent += nexp;
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rr->m_apm_sign = aa->m_apm_sign;
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M_restore_stack(6);
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}
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/****************************************************************************/
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