[DTrace-devel] [PATCH v2 10/20] Optimize dt_strtab_insert() for empty string
Kris Van Hees
kris.van.hees at oracle.com
Thu Jun 3 08:17:16 PDT 2021
This patch also clarifies that the string table will always have the
empty string at offset 0.
Signed-off-by: Kris Van Hees <kris.van.hees at oracle.com>
---
libdtrace/dt_strtab.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/libdtrace/dt_strtab.c b/libdtrace/dt_strtab.c
index 9f5ae23f..ff32606f 100644
--- a/libdtrace/dt_strtab.c
+++ b/libdtrace/dt_strtab.c
@@ -1,6 +1,6 @@
/*
* Oracle Linux DTrace.
- * Copyright (c) 2006, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2006, 2021, Oracle and/or its affiliates. All rights reserved.
* Licensed under the Universal Permissive License v 1.0 as shown at
* http://oss.oracle.com/licenses/upl.
*/
@@ -65,6 +65,11 @@ dt_strtab_create(size_t bufsz)
if (dt_strtab_grow(sp) == -1)
goto err;
+ /*
+ * Pre-populate the string table with the empty string as frist string,
+ * at offset 0. We use this guarantee in dt_strtab_insert() and
+ * dt_strtab_index().
+ */
*sp->str_ptr++ = '\0';
return sp;
@@ -192,7 +197,7 @@ dt_strtab_index(dt_strtab_t *sp, const char *str)
ulong_t h;
if (str == NULL || str[0] == '\0')
- return 0; /* we keep a \0 at offset 0 to simplify things */
+ return 0; /* The empty string is always at offset 0. */
h = dt_strtab_hash(str, &len) % sp->str_hashsz;
@@ -212,6 +217,9 @@ dt_strtab_insert(dt_strtab_t *sp, const char *str)
ssize_t off;
ulong_t h;
+ if (str == NULL || str[0] == '\0')
+ return 0; /* The empty string is always at offset 0. */
+
if ((off = dt_strtab_index(sp, str)) != -1)
return off;
--
2.31.1
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