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Add commentary about Cygwin's broken erand48, per report from Andrew Dunstan.

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This commit is contained in:
Tom Lane
2009-07-24 15:03:07 +00:00
parent dc7aa36521
commit 655473a7cd
3 changed files with 20 additions and 10 deletions
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22
src/backend/optimizer/geqo/geqo_selection.c
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@ -6,7 +6,7 @@
* Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_selection.c,v 1.25 2009/07/16 20:55:44 tgl Exp $
* $PostgreSQL: pgsql/src/backend/optimizer/geqo/geqo_selection.c,v 1.26 2009/07/24 15:03:07 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -42,7 +42,7 @@
#include "optimizer/geqo_random.h"
#include "optimizer/geqo_selection.h"
static int linear(PlannerInfo *root, int max, double bias);
static int linear_rand(PlannerInfo *root, int max, double bias);
/*
@ -57,13 +57,21 @@ geqo_selection(PlannerInfo *root, Chromosome *momma, Chromosome *daddy,
int first,
second;
first = linear(root, pool->size, bias);
second = linear(root, pool->size, bias);
first = linear_rand(root, pool->size, bias);
second = linear_rand(root, pool->size, bias);
/*
* Ensure we have selected different genes, except if pool size is only
* one, when we can't.
*
* This code has been observed to hang up in an infinite loop when the
* platform's implementation of erand48() is broken. We consider that a
* feature: it lets you know you'd better fix the random-number generator.
*/
if (pool->size > 1)
{
while (first == second)
second = linear(root, pool->size, bias);
second = linear_rand(root, pool->size, bias);
}
geqo_copy(root, momma, &pool->data[first], pool->string_length);
@ -71,7 +79,7 @@ geqo_selection(PlannerInfo *root, Chromosome *momma, Chromosome *daddy,
}
/*
* linear
* linear_rand
* generates random integer between 0 and input max number
* using input linear bias
*
@ -81,7 +89,7 @@ geqo_selection(PlannerInfo *root, Chromosome *momma, Chromosome *daddy,
* bias = (prob of first rule) / (prob of middle rule)
*/
static int
linear(PlannerInfo *root, int pool_size, double bias)
linear_rand(PlannerInfo *root, int pool_size, double bias)
{
double index; /* index between 0 and pop_size */
double max = (double) pool_size;