linux-kernel - [PATCH nolibc 46/61] tools/nolibc/string: add strcmp() and strncmp()

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Date:   Mon, 18 Apr 2022 17:42:10 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     gwml@...r.gnuweeb.org, kernel-team@...com, w@....eu,
        Willy Tarreau <w@....eu>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH nolibc 46/61] tools/nolibc/string: add strcmp() and strncmp()

From: Willy Tarreau <w@....eu>

We need these functions all the time, including when checking environment
variables and parsing command-line arguments. These implementations were
optimized to show optimal code size on a wide range of compilers (22 bytes
return included for strcmp(), 33 for strncmp()).

Signed-off-by: Willy Tarreau <w@....eu>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 tools/include/nolibc/string.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h
index 4554b6fcb400..0d5e870c7c0b 100644
--- a/tools/include/nolibc/string.h
+++ b/tools/include/nolibc/string.h
@@ -102,6 +102,17 @@ char *strchr(const char *s, int c)
 	return NULL;
 }
 
+static __attribute__((unused))
+int strcmp(const char *a, const char *b)
+{
+	unsigned int c;
+	int diff;
+
+	while (!(diff = (unsigned char)*a++ - (c = (unsigned char)*b++)) && c)
+		;
+	return diff;
+}
+
 static __attribute__((unused))
 char *strcpy(char *dst, const char *src)
 {
@@ -184,6 +195,18 @@ char *strncat(char *dst, const char *src, size_t size)
 	return orig;
 }
 
+static __attribute__((unused))
+int strncmp(const char *a, const char *b, size_t size)
+{
+	unsigned int c;
+	int diff = 0;
+
+	while (size-- &&
+	       !(diff = (unsigned char)*a++ - (c = (unsigned char)*b++)) && c)
+		;
+
+	return diff;
+}
 
 static __attribute__((unused))
 char *strncpy(char *dst, const char *src, size_t size)
-- 
2.31.1.189.g2e36527f23