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116 lines
3.4 KiB
C
116 lines
3.4 KiB
C
/*-------------------------------------------------------------------------
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*
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* geqo_selection.c
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* linear selection scheme for the genetic query optimizer
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*
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* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/backend/optimizer/geqo/geqo_selection.c
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*
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*-------------------------------------------------------------------------
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*/
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/* contributed by:
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=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
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* Martin Utesch * Institute of Automatic Control *
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= = University of Mining and Technology =
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* utesch@aut.tu-freiberg.de * Freiberg, Germany *
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=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
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*/
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/* this is adopted from D. Whitley's Genitor algorithm */
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/*************************************************************/
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/* */
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/* Copyright (c) 1990 */
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/* Darrell L. Whitley */
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/* Computer Science Department */
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/* Colorado State University */
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/* */
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/* Permission is hereby granted to copy all or any part of */
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/* this program for free distribution. The author's name */
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/* and this copyright notice must be included in any copy. */
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/* */
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/*************************************************************/
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#include "postgres.h"
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#include <math.h>
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#include "optimizer/geqo_copy.h"
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#include "optimizer/geqo_random.h"
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#include "optimizer/geqo_selection.h"
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static int linear_rand(PlannerInfo *root, int max, double bias);
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/*
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* geqo_selection
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* according to bias described by input parameters,
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* first and second genes are selected from the pool
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*/
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void
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geqo_selection(PlannerInfo *root, Chromosome *momma, Chromosome *daddy,
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Pool *pool, double bias)
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{
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int first,
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second;
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first = linear_rand(root, pool->size, bias);
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second = linear_rand(root, pool->size, bias);
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/*
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* Ensure we have selected different genes, except if pool size is only
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* one, when we can't.
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*
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* This code was observed to hang up in an infinite loop when the
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* platform's implementation of erand48() was broken. We now always use
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* our own version.
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*/
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if (pool->size > 1)
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{
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while (first == second)
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second = linear_rand(root, pool->size, bias);
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}
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geqo_copy(root, momma, &pool->data[first], pool->string_length);
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geqo_copy(root, daddy, &pool->data[second], pool->string_length);
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}
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/*
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* linear_rand
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* generates random integer between 0 and input max number
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* using input linear bias
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*
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* bias is y-intercept of linear distribution
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*
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* probability distribution function is: f(x) = bias - 2(bias - 1)x
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* bias = (prob of first rule) / (prob of middle rule)
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*/
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static int
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linear_rand(PlannerInfo *root, int pool_size, double bias)
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{
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double index; /* index between 0 and pool_size */
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double max = (double) pool_size;
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/*
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* If geqo_rand() returns exactly 1.0 then we will get exactly max from
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* this equation, whereas we need 0 <= index < max. Also it seems
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* possible that roundoff error might deliver values slightly outside the
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* range; in particular avoid passing a value slightly less than 0 to
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* sqrt(). If we get a bad value just try again.
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*/
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do
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{
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double sqrtval;
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sqrtval = (bias * bias) - 4.0 * (bias - 1.0) * geqo_rand(root);
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if (sqrtval > 0.0)
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sqrtval = sqrt(sqrtval);
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index = max * (bias - sqrtval) / 2.0 / (bias - 1.0);
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} while (index < 0.0 || index >= max);
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return (int) index;
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}
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