From 318509212d6baf224000a209c793c4fb22c58c7e Mon Sep 17 00:00:00 2001
From: Andreas Kloeckner <inform@tiker.net>
Date: Tue, 31 Jul 2012 00:21:20 -0400
Subject: [PATCH] Scan: allow output_statement to reference last_item if
non-segmented.
---
pyopencl/scan.py | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/pyopencl/scan.py b/pyopencl/scan.py
index 6217de59..526f679c 100644
--- a/pyopencl/scan.py
+++ b/pyopencl/scan.py
@@ -559,7 +559,10 @@ void ${name_prefix}_final_update(
%if is_segmented:
const index_type first_seg_start_in_interval =
g_first_segment_start_in_interval[GID_0];
+ %endif
+ %if not is_segmented and 'last_item' in output_statement:
+ scan_type last_item = interval_results[GDIM_0-1];
%endif
%if not use_lookbehind_update:
@@ -851,19 +854,23 @@ class _GenericScanKernelBase(object):
in the values to which the scan is applied. This may be used
to apply a mapping to values stored in *arguments* before being
scanned. The result of this expression must match *dtype*.
- The index intended to be mapped is available as *i* in this
+ The index intended to be mapped is available as `i` in this
expression. This expression may also use the variables defined
by *input_fetch_expr*.
This expression may also call functions given in the *preamble*.
:arg output_statement: a C statement that writes
- the output of the scan. It has access to the scan result as *item*,
- the preceding scan result item as *prev_item*, and the current index
- as *i*. *prev_item* in a segmented scan will be the neutral element
+ the output of the scan. It has access to the scan result as `item`,
+ the preceding scan result item as `prev_item`, and the current index
+ as `i`. `prev_item` in a segmented scan will be the neutral element
at a segment boundary, not the immediately preceding item.
Using *prev_item* in output statement has a small run-time cost.
- *prev_item* enables the construction of an exclusive scan.
+ `prev_item` enables the construction of an exclusive scan.
+
+ For non-segmented scans, *output_statement* may also reference
+ `last_item`, which evaluates to the scan result of the last
+ array entry.
:arg is_segment_start_expr: A C expression, encoded as a string,
resulting in a C `bool` value that determines whether a new
scan segments starts at index *i*. If given, makes the scan a
--
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