On Wed, 2025-03-12 at 19:55 +0300, Alexander Borisov wrote:
> 1. Added static for casemap() function. Otherwise the compiler could
> not
> optimize the code and the performance dropped significantly.
Oops, it was static, but I made it external just to see what code it
generated. I didn't intend to publish it as an external function --
thank you for catching that!
> 2. Added a fast path for codepoint < 0x80.
>
> v3j-0002:
> In the fast path for codepoints < 0x80, I added a premature return.
> This avoided additional insertions, which increased performance.
What do you mean "additional insertions"?
Also, should we just compute the results in the fast path? We don't
even need a table. Rough patch attached to go on top of v4-0001.
Should we properly return CASEMAP_SELF when *simple == u1, or is it ok
to return CASEMAP_SIMPLE? It probably doesn't matter performance-wise,
but it feels more correct to return CASEMAP_SELF.
>
> Perhaps for general
> beauty it should be made static inline, I don't have a rigid position
> here.
We ordinarily use "static inline" if it's in a header file, and
"static" if it's in a .c file, so I'll do it that way.
> I was purely based on existing approaches in Postgres, the
> Normalization Forms have them separated into different headers. Just
> trying to be consistent with existing approaches.
I think that was done for normalization primarily because it's not used
#ifndef FRONTEND (see unicode_norm.c), and perhaps also because it's
just a more complex function worthy of its own file.
I looked into the history, and commit 783f0cc64d explains why perfect
hashing is not used in the frontend:
"The decomposition table remains the same, getting used for the binary
search in the frontend code, where we care more about the size of the
libraries like libpq over performance..."
>
Regards,
Jeff Davis
From ed4d2803aa32add7c05726286b94e78e49bb1257 Mon Sep 17 00:00:00 2001
From: Jeff Davis <[email protected]>
Date: Wed, 12 Mar 2025 11:56:59 -0700
Subject: [PATCH vtmp] fastpath
---
src/common/unicode_case.c | 34 ++++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)
diff --git a/src/common/unicode_case.c b/src/common/unicode_case.c
index 2b3b4cdc2e7..b1fc1651043 100644
--- a/src/common/unicode_case.c
+++ b/src/common/unicode_case.c
@@ -390,11 +390,41 @@ casemap(pg_wchar u1, CaseKind casekind, bool full,
{
const pg_case_map *map;
+ /*
+ * Fast path for early codepoints. The only interesting characters are
+ * [a-zA-Z].
+ */
if (u1 < 0x80)
{
- *simple = case_map[u1].simplemap[casekind];
+ /* fast-path codepoints do not have special casing */
+ Assert(find_case_map(u1)->special_case == NULL);
- return CASEMAP_SIMPLE;
+ switch (casekind)
+ {
+ case CaseLower:
+ case CaseFold:
+ if (u1 >= 'A' && u1 <= 'Z')
+ {
+ *simple = u1 + 0x20;
+ Assert(case_map[u1].simplemap[casekind] == *simple);
+ return CASEMAP_SIMPLE;
+ }
+ break;
+ case CaseTitle:
+ case CaseUpper:
+ if (u1 >= 'a' && u1 <= 'z')
+ {
+ *simple = u1 - 0x20;
+ Assert(case_map[u1].simplemap[casekind] == *simple);
+ return CASEMAP_SIMPLE;
+ }
+ break;
+ default:
+ Assert(false);
+ }
+
+ Assert(case_map[u1].simplemap[casekind] == u1);
+ return CASEMAP_SELF;
}
map = find_case_map(u1);
--
2.34.1
