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Message-Id: <20200304092701.19154-1-timo.teras@iki.fi>
Date: Wed, 4 Mar 2020 11:27:01 +0200
From: Timo Teräs <timo.teras@....fi>
To: musl@...ts.openwall.com
Cc: Timo Teräs <timo.teras@....fi>
Subject: [PATCH v2] improve strerror speed
change the current O(n) lookup to O(1) based on the machinery
described in "How To Write Shared Libraries" (Appendix B).
---
src/errno/__strerror.h | 13 ++++++-------
src/errno/strerror.c | 41 ++++++++++++++++++++++++++---------------
2 files changed, 32 insertions(+), 22 deletions(-)
diff --git a/src/errno/__strerror.h b/src/errno/__strerror.h
index 2f04d400..2d992da5 100644
--- a/src/errno/__strerror.h
+++ b/src/errno/__strerror.h
@@ -1,8 +1,9 @@
-/* This file is sorted such that 'errors' which represent exceptional
- * conditions under which a correct program may fail come first, followed
- * by messages that indicate an incorrect program or system failure. The
- * macro E() along with double-inclusion is used to ensure that ordering
- * of the strings remains synchronized. */
+/* The first entry is a catch-all for codes not enumerated here.
+ * This file is included multiple times to declare and define a structure
+ * with these messages, and then to define a lookup table translating
+ * error codes to offsets of corresponding fields in the structure. */
+
+E(0, "No error information")
E(EILSEQ, "Illegal byte sequence")
E(EDOM, "Domain error")
@@ -101,5 +102,3 @@ E(EDQUOT, "Quota exceeded")
E(ENOMEDIUM, "No medium found")
E(EMEDIUMTYPE, "Wrong medium type")
E(EMULTIHOP, "Multihop attempted")
-
-E(0, "No error information")
diff --git a/src/errno/strerror.c b/src/errno/strerror.c
index e3ed771a..918fbce9 100644
--- a/src/errno/strerror.c
+++ b/src/errno/strerror.c
@@ -1,30 +1,41 @@
#include <errno.h>
+#include <stddef.h>
#include <string.h>
#include "locale_impl.h"
-#define E(a,b) ((unsigned char)a),
-static const unsigned char errid[] = {
+/* mips has one error code outside of the 8-bit range due to a
+ * historical typo, so we just remap it. */
+#if EDQUOT==1133
+#define EDQUOT_ORIG 1133
+#undef EDQUOT
+#define EDQUOT 109
+#endif
+
+static const struct errmsgstr_t {
+#define E(n, s) char str##n[sizeof(s)];
+#include "__strerror.h"
+#undef E
+} errmsgstr = {
+#define E(n, s) s,
#include "__strerror.h"
+#undef E
};
-#undef E
-#define E(a,b) b "\0"
-static const char errmsg[] =
+static const unsigned short errmsgidx[] = {
+#define E(n, s) [n] = offsetof(struct errmsgstr_t, str##n),
#include "__strerror.h"
-;
+#undef E
+};
char *__strerror_l(int e, locale_t loc)
{
const char *s;
- int i;
- /* mips has one error code outside of the 8-bit range due to a
- * historical typo, so we just remap it. */
- if (EDQUOT==1133) {
- if (e==109) e=-1;
- else if (e==EDQUOT) e=109;
- }
- for (i=0; errid[i] && errid[i] != e; i++);
- for (s=errmsg; i; s++, i--) for (; *s; s++);
+#ifdef EDQUOT_ORIG
+ if (e==EDQUOT) e=0;
+ else if (e==EDQUOT_ORIG) e=EDQUOT;
+#endif
+ if ((size_t)e >= sizeof errmsgidx / sizeof *errmsgidx) e = 0;
+ s = (char *)&errmsgstr + errmsgidx[e];
return (char *)LCTRANS(s, LC_MESSAGES, loc);
}
--
2.25.1
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