On Wed, Mar 27, 2024 at 05:10:13PM -0400, Tom Lane wrote:
> Shouldn't "i" be declared uint32, since nelem is?
Yes, that's a mistake.
> BTW, I wonder why these functions don't declare their array
> arguments like "const uint32 *base".
They probably should. I don't see any reason not to, and my compiler
doesn't complain, either.
> LGTM otherwise, and I like the fact that the #if structure
> gets a lot less messy.
Thanks for reviewing. I've attached a v2 that I intend to commit when I
get a chance.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
>From 6f2577779917230bf70284f0ec1186bed17d9b4a Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nat...@postgresql.org>
Date: Wed, 27 Mar 2024 13:50:17 -0500
Subject: [PATCH v2 1/1] improve style of pg_lfind32()
---
src/include/port/pg_lfind.h | 62 ++++++++++++++++---------------------
1 file changed, 26 insertions(+), 36 deletions(-)
diff --git a/src/include/port/pg_lfind.h b/src/include/port/pg_lfind.h
index 33e8471b03..4b1431ed00 100644
--- a/src/include/port/pg_lfind.h
+++ b/src/include/port/pg_lfind.h
@@ -80,6 +80,24 @@ pg_lfind8_le(uint8 key, uint8 *base, uint32 nelem)
return false;
}
+/*
+ * pg_lfind32_one_by_one_helper
+ *
+ * Searches the array of integers one-by-one. The caller is responsible for
+ * ensuring that there are at least "nelem" integers in the array.
+ */
+static inline bool
+pg_lfind32_one_by_one_helper(uint32 key, const uint32 *base, uint32 nelem)
+{
+ for (uint32 i = 0; i < nelem; i++)
+ {
+ if (key == base[i])
+ return true;
+ }
+
+ return false;
+}
+
#ifndef USE_NO_SIMD
/*
* pg_lfind32_simd_helper
@@ -88,7 +106,7 @@ pg_lfind8_le(uint8 key, uint8 *base, uint32 nelem)
* ensuring that there are at least 4-registers-worth of integers remaining.
*/
static inline bool
-pg_lfind32_simd_helper(const Vector32 keys, uint32 *base)
+pg_lfind32_simd_helper(const Vector32 keys, const uint32 *base)
{
const uint32 nelem_per_vector = sizeof(Vector32) / sizeof(uint32);
Vector32 vals1,
@@ -132,11 +150,10 @@ pg_lfind32_simd_helper(const Vector32 keys, uint32 *base)
* return false.
*/
static inline bool
-pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
+pg_lfind32(uint32 key, const uint32 *base, uint32 nelem)
{
- uint32 i = 0;
-
#ifndef USE_NO_SIMD
+ uint32 i = 0;
/*
* For better instruction-level parallelism, each loop iteration operates
@@ -150,25 +167,15 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
const uint32 tail_idx = nelem & ~(nelem_per_iteration - 1);
#if defined(USE_ASSERT_CHECKING)
- bool assert_result = false;
-
- /* pre-compute the result for assert checking */
- for (int j = 0; j < nelem; j++)
- {
- if (key == base[j])
- {
- assert_result = true;
- break;
- }
- }
+ bool assert_result = pg_lfind32_one_by_one_helper(key, base, nelem);
#endif
/*
- * If there aren't enough elements for the SIMD code, jump to the standard
+ * If there aren't enough elements for the SIMD code, use the standard
* one-by-one linear search code.
*/
if (nelem < nelem_per_iteration)
- goto one_by_one;
+ return pg_lfind32_one_by_one_helper(key, base, nelem);
/*
* Process as many elements as possible with a block of 4 registers.
@@ -193,27 +200,10 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
*/
Assert(assert_result == pg_lfind32_simd_helper(keys, &base[nelem - nelem_per_iteration]));
return pg_lfind32_simd_helper(keys, &base[nelem - nelem_per_iteration]);
-
-one_by_one:
-
-#endif /* ! USE_NO_SIMD */
-
+#else
/* Process the elements one at a time. */
- for (; i < nelem; i++)
- {
- if (key == base[i])
- {
-#ifndef USE_NO_SIMD
- Assert(assert_result == true);
+ return pg_lfind32_one_by_one_helper(key, base, nelem);
#endif
- return true;
- }
- }
-
-#ifndef USE_NO_SIMD
- Assert(assert_result == false);
-#endif
- return false;
}
#endif /* PG_LFIND_H */
--
2.25.1
