/* PSPP - a program for statistical analysis.
- Copyright (C) 2007, 2009 Free Software Foundation, Inc.
+ Copyright (C) 2007, 2009, 2010 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
#include <config.h>
-#include <data/casereader.h>
-#include <data/casereader-provider.h>
+#include "data/casereader.h"
+#include "data/casereader-provider.h"
#include <stdlib.h>
-#include <data/casewindow.h>
-#include <data/casewriter.h>
-#include <data/settings.h>
-#include <libpspp/assertion.h>
-#include <libpspp/heap.h>
-#include <libpspp/taint.h>
+#include "data/casereader-shim.h"
+#include "data/casewriter.h"
+#include "libpspp/assertion.h"
+#include "libpspp/heap.h"
+#include "libpspp/taint.h"
-#include "xalloc.h"
+#include "gl/xalloc.h"
/* A casereader. */
struct casereader
void *aux; /* Auxiliary data for class. */
};
-static void insert_shim (struct casereader *);
-
/* Reads and returns the next case from READER. The caller owns
the returned case and must call case_unref on it when its data
is no longer needed. Returns a null pointer if cases have
return NULL;
if (reader->class->clone == NULL)
- insert_shim (reader);
+ casereader_shim_insert (reader);
clone = reader->class->clone (reader, reader->aux);
assert (clone != NULL);
assert (clone != reader);
{
struct ccase *c;
if (reader->class->peek == NULL)
- insert_shim (reader);
+ casereader_shim_insert (reader);
c = reader->class->peek (reader, reader->aux, idx);
if (c != NULL)
return c;
random_reader_peek,
};
\f
-/* Buffering shim for implementing clone and peek operations.
-
- The "clone" and "peek" operations aren't implemented by all
- types of casereaders, but we have to expose a uniform
- interface anyhow. We do this by interposing a buffering
- casereader on top of the existing casereader on the first call
- to "clone" or "peek". The buffering casereader maintains a
- window of cases that spans the positions of the original
- casereader and all of its clones (the "clone set"), from the
- position of the casereader that has read the fewest cases to
- the position of the casereader that has read the most.
-
- Thus, if all of the casereaders in the clone set are at
- approximately the same position, only a few cases are buffered
- and there is little inefficiency. If, on the other hand, one
- casereader is not used to read any cases at all, but another
- one is used to read all of the cases, the entire contents of
- the casereader is copied into the buffer. This still might
- not be so inefficient, given that case data in memory is
- shared across multiple identical copies, but in the worst case
- the window implementation will write cases to disk instead of
- maintaining them in-memory. */
-
-/* A buffering shim for a non-clonable or non-peekable
- casereader. */
-struct shim
- {
- struct casewindow *window; /* Window of buffered cases. */
- struct casereader *subreader; /* Subordinate casereader. */
- };
-
-static const struct casereader_random_class shim_class;
-
-/* Interposes a buffering shim atop READER. */
-static void
-insert_shim (struct casereader *reader)
-{
- const struct caseproto *proto = casereader_get_proto (reader);
- casenumber case_cnt = casereader_get_case_cnt (reader);
- struct shim *b = xmalloc (sizeof *b);
- b->window = casewindow_create (proto, settings_get_workspace_cases (proto));
- b->subreader = casereader_create_random (proto, case_cnt, &shim_class, b);
- casereader_swap (reader, b->subreader);
- taint_propagate (casewindow_get_taint (b->window),
- casereader_get_taint (reader));
- taint_propagate (casereader_get_taint (b->subreader),
- casereader_get_taint (reader));
-}
-
-/* Ensures that B's window contains at least CASE_CNT cases.
- Return true if successful, false upon reaching the end of B's
- subreader or an I/O error. */
-static bool
-prime_buffer (struct shim *b, casenumber case_cnt)
-{
- while (casewindow_get_case_cnt (b->window) < case_cnt)
- {
- struct ccase *tmp = casereader_read (b->subreader);
- if (tmp == NULL)
- return false;
- casewindow_push_head (b->window, tmp);
- }
- return true;
-}
-
-/* Reads the case at the given 0-based OFFSET from the front of
- the window into C. Returns the case if successful, or a null
- pointer if OFFSET is beyond the end of file or upon I/O error.
- The caller must call case_unref() on the returned case when it
- is no longer needed. */
-static struct ccase *
-shim_read (struct casereader *reader UNUSED, void *b_,
- casenumber offset)
-{
- struct shim *b = b_;
- if (!prime_buffer (b, offset + 1))
- return NULL;
- return casewindow_get_case (b->window, offset);
-}
-
-/* Destroys B. */
-static void
-shim_destroy (struct casereader *reader UNUSED, void *b_)
-{
- struct shim *b = b_;
- casewindow_destroy (b->window);
- casereader_destroy (b->subreader);
- free (b);
-}
-
-/* Discards CNT cases from the front of B's window. */
-static void
-shim_advance (struct casereader *reader UNUSED, void *b_, casenumber case_cnt)
-{
- struct shim *b = b_;
- casewindow_pop_tail (b->window, case_cnt);
-}
-
-/* Class for the buffered reader. */
-static const struct casereader_random_class shim_class =
- {
- shim_read,
- shim_destroy,
- shim_advance,
- };
\f
static const struct casereader_class casereader_null_class;
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