From: Willy Tarreau <w@1wt.eu>
To: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Mark Brown <broonie@kernel.org>,
linux-kernel@vger.kernel.org, Willy Tarreau <w@1wt.eu>
Subject: [PATCH 15/42] tools/nolibc/stdlib: replace the ltoa() function with more efficient ones
Date: Mon, 7 Feb 2022 17:23:27 +0100 [thread overview]
Message-ID: <20220207162354.14293-16-w@1wt.eu> (raw)
In-Reply-To: <20220207162354.14293-1-w@1wt.eu>
The original ltoa() function and the reentrant one ltoa_r() present a
number of drawbacks. The divide by 10 generates calls to external code
from libgcc_s, and the number does not necessarily start at the beginning
of the buffer.
Let's rewrite these functions so that they do not involve a divide and
only use loops on powers of 10, and implement both signed and unsigned
variants, always starting from the buffer's first character. Instead of
using a static buffer for each function, we're now using a common one.
In order to avoid confusion with the ltoa() name, the new functions are
called itoa_r() and utoa_r() to distinguish the signed and unsigned
versions, and for convenience for their callers, these functions now
reutrn the number of characters emitted. The ltoa_r() function is just
an inline mapping to the signed one and which returns the buffer.
The functions are quite small (86 bytes on x86_64, 68 on armv7) and
do not depend anymore on external code.
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
tools/include/nolibc/stdlib.h | 107 +++++++++++++++++++++++++++-------
1 file changed, 87 insertions(+), 20 deletions(-)
diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 84fc4353fb01..dbb45631c7ca 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -12,6 +12,13 @@
#include "types.h"
#include "sys.h"
+
+/* Buffer used to store int-to-ASCII conversions. Will only be implemented if
+ * any of the related functions is implemented. The area is large enough to
+ * store "18446744073709551615" or "-9223372036854775808" and the final zero.
+ */
+static __attribute__((unused)) char itoa_buffer[21];
+
/*
* As much as possible, please keep functions alphabetically sorted.
*/
@@ -45,36 +52,96 @@ int atoi(const char *s)
return atol(s);
}
-/* performs the opposite of atol() using a user-fed buffer. The buffer must be
- * at least 21 bytes long (large enough for "-9223372036854775808").
+/* Converts the unsigned long integer <in> to its string representation into
+ * buffer <buffer>, which must be long enough to store the number and the
+ * trailing zero (21 bytes for 18446744073709551615 in 64-bit, 11 for
+ * 4294967295 in 32-bit). The buffer is filled from the first byte, and the
+ * number of characters emitted (not counting the trailing zero) is returned.
+ * The function is constructed in a way to optimize the code size and avoid
+ * any divide that could add a dependency on large external functions.
*/
static __attribute__((unused))
-const char *ltoa_r(long in, char *buffer)
+int utoa_r(unsigned long in, char *buffer)
{
- char *pos = buffer + 21 - 1;
- int neg = in < 0;
- unsigned long n = neg ? -in : in;
+ unsigned long lim;
+ int digits = 0;
+ int pos = (~0UL > 0xfffffffful) ? 19 : 9;
+ int dig;
- *pos-- = '\0';
do {
- *pos-- = '0' + n % 10;
- n /= 10;
- if (pos < buffer)
- return pos + 1;
- } while (n);
+ for (dig = 0, lim = 1; dig < pos; dig++)
+ lim *= 10;
- if (neg)
- *pos-- = '-';
- return pos + 1;
+ if (digits || in >= lim || !pos) {
+ for (dig = 0; in >= lim; dig++)
+ in -= lim;
+ buffer[digits++] = '0' + dig;
+ }
+ } while (pos--);
+
+ buffer[digits] = 0;
+ return digits;
}
-/* performs the opposite of atol() using a statically allocated buffer */
+/* Converts the signed long integer <in> to its string representation into
+ * buffer <buffer>, which must be long enough to store the number and the
+ * trailing zero (21 bytes for -9223372036854775808 in 64-bit, 12 for
+ * -2147483648 in 32-bit). The buffer is filled from the first byte, and the
+ * number of characters emitted (not counting the trailing zero) is returned.
+ */
static __attribute__((unused))
-const char *ltoa(long in)
+int itoa_r(long in, char *buffer)
{
- /* large enough for -9223372036854775808 */
- static char buffer[21];
- return ltoa_r(in, buffer);
+ char *ptr = buffer;
+ int len = 0;
+
+ if (in < 0) {
+ in = -in;
+ *(ptr++) = '-';
+ len++;
+ }
+ len += utoa_r(in, ptr);
+ return len;
+}
+
+/* for historical compatibility, same as above but returns the pointer to the
+ * buffer.
+ */
+static inline __attribute__((unused))
+char *ltoa_r(long in, char *buffer)
+{
+ itoa_r(in, buffer);
+ return buffer;
+}
+
+/* converts long integer <in> to a string using the static itoa_buffer and
+ * returns the pointer to that string.
+ */
+static inline __attribute__((unused))
+char *itoa(long in)
+{
+ itoa_r(in, itoa_buffer);
+ return itoa_buffer;
+}
+
+/* converts long integer <in> to a string using the static itoa_buffer and
+ * returns the pointer to that string. Same as above, for compatibility.
+ */
+static inline __attribute__((unused))
+char *ltoa(long in)
+{
+ itoa_r(in, itoa_buffer);
+ return itoa_buffer;
+}
+
+/* converts unsigned long integer <in> to a string using the static itoa_buffer
+ * and returns the pointer to that string.
+ */
+static inline __attribute__((unused))
+char *utoa(unsigned long in)
+{
+ utoa_r(in, itoa_buffer);
+ return itoa_buffer;
}
static __attribute__((unused))
--
2.35.1
next prev parent reply other threads:[~2022-02-07 16:33 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-07 16:23 [PATCH 00/42] nolibc: update to resync with out-of-tree project Willy Tarreau
2022-02-07 16:23 ` [PATCH 01/42] tools/nolibc: use pselect6 on RISCV Willy Tarreau
2022-02-07 16:23 ` [PATCH 02/42] tools/nolibc: guard the main file against multiple inclusion Willy Tarreau
2022-02-07 16:23 ` [PATCH 03/42] tools/nolibc/std: move the standard type definitions to std.h Willy Tarreau
2022-02-07 16:23 ` [PATCH 04/42] tools/nolibc/types: split syscall-specific definitions into their own files Willy Tarreau
2022-02-07 16:23 ` [PATCH 05/42] tools/nolibc/arch: split arch-specific code into individual files Willy Tarreau
2022-02-07 16:23 ` [PATCH 06/42] tools/nolibc/sys: split the syscall definitions into their own file Willy Tarreau
2022-02-07 16:23 ` [PATCH 07/42] tools/nolibc/stdlib: extract the stdlib-specific functions to " Willy Tarreau
2022-02-07 16:23 ` [PATCH 08/42] tools/nolibc/string: split the string functions into string.h Willy Tarreau
2022-02-07 16:23 ` [PATCH 09/42] tools/nolibc/ctype: split the is* functions to ctype.h Willy Tarreau
2022-02-07 16:23 ` [PATCH 10/42] tools/nolibc/ctype: add the missing is* functions Willy Tarreau
2022-02-07 16:23 ` [PATCH 11/42] tools/nolibc/types: move the FD_* functions to macros in types.h Willy Tarreau
2022-02-07 17:05 ` David Laight
2022-02-08 5:14 ` Willy Tarreau
2022-02-13 8:52 ` [PATCH v2 " Willy Tarreau
2022-02-07 16:23 ` [PATCH 12/42] tools/nolibc/types: make FD_SETSIZE configurable Willy Tarreau
2022-02-13 8:53 ` [PATCH v2 " Willy Tarreau
2022-02-14 20:17 ` Paul E. McKenney
2022-02-07 16:23 ` [PATCH 13/42] tools/nolibc/types: move makedev to types.h and make it a macro Willy Tarreau
2022-02-07 16:23 ` [PATCH 14/42] tools/nolibc/stdlib: move ltoa() to stdlib.h Willy Tarreau
2022-02-07 16:23 ` Willy Tarreau [this message]
2022-02-07 16:23 ` [PATCH 16/42] tools/nolibc/stdlib: add i64toa() and u64toa() Willy Tarreau
2022-02-07 16:23 ` [PATCH 17/42] tools/nolibc/stdlib: add utoh() and u64toh() Willy Tarreau
2022-02-07 16:23 ` [PATCH 18/42] tools/nolibc/stdio: add a minimal set of stdio functions Willy Tarreau
2022-02-07 16:23 ` [PATCH 19/42] tools/nolibc/stdio: add stdin/stdout/stderr and fget*/fput* functions Willy Tarreau
2022-02-07 16:23 ` [PATCH 20/42] tools/nolibc/stdio: add fwrite() to stdio Willy Tarreau
2022-02-07 16:23 ` [PATCH 21/42] tools/nolibc/stdio: add a minimal [vf]printf() implementation Willy Tarreau
2022-02-07 16:23 ` [PATCH 22/42] tools/nolibc/types: define EXIT_SUCCESS and EXIT_FAILURE Willy Tarreau
2022-02-07 16:23 ` [PATCH 23/42] tools/nolibc/stdio: add perror() to report the errno value Willy Tarreau
2022-02-07 16:23 ` [PATCH 24/42] tools/nolibc/sys: make open() take a vararg on the 3rd argument Willy Tarreau
2022-02-07 16:23 ` [PATCH 25/42] tools/nolibc/stdlib: avoid a 64-bit shift in u64toh_r() Willy Tarreau
2022-02-07 16:23 ` [PATCH 26/42] tools/nolibc/stdlib: make raise() use the lower level syscalls only Willy Tarreau
2022-02-07 16:23 ` [PATCH 27/42] tools/nolibc/sys: make getpgrp(), getpid(), gettid() not set errno Willy Tarreau
2022-02-07 16:23 ` [PATCH 28/42] tools/nolibc/string: use unidirectional variants for memcpy() Willy Tarreau
2022-02-07 16:23 ` [PATCH 29/42] tools/nolibc/string: slightly simplify memmove() Willy Tarreau
2022-02-07 16:23 ` [PATCH 30/42] tools/nolibc/string: add strncpy() and strlcpy() Willy Tarreau
2022-02-07 16:23 ` [PATCH 31/42] tools/nolibc/string: add tiny versions of strncat() and strlcat() Willy Tarreau
2022-02-07 16:23 ` [PATCH 32/42] tools/nolibc: move exported functions to their own section Willy Tarreau
2022-02-07 16:23 ` [PATCH 33/42] tools/nolibc/arch: mark the _start symbol as weak Willy Tarreau
2022-02-07 16:23 ` [PATCH 34/42] tools/nolibc/types: define PATH_MAX and MAXPATHLEN Willy Tarreau
2022-02-07 16:23 ` [PATCH 35/42] tools/nolibc/string: export memset() and memmove() Willy Tarreau
2022-02-07 16:23 ` [PATCH 36/42] tools/nolibc/errno: extract errno.h from sys.h Willy Tarreau
2022-02-07 16:23 ` [PATCH 37/42] tools/nolibc/unistd: extract msleep(), sleep(), tcsetpgrp() to unistd.h Willy Tarreau
2022-02-07 16:23 ` [PATCH 38/42] tools/nolibc/unistd: add usleep() Willy Tarreau
2022-02-07 16:23 ` [PATCH 39/42] tools/nolibc/signal: move raise() to signal.h Willy Tarreau
2022-02-07 16:23 ` [PATCH 40/42] tools/nolibc/time: create time.h with time() Willy Tarreau
2022-02-07 16:23 ` [PATCH 41/42] tools/nolibc: also mention how to build by just setting the include path Willy Tarreau
2022-02-07 16:23 ` [PATCH 42/42] tools/nolibc/stdlib: implement abort() Willy Tarreau
2022-02-08 0:00 ` [PATCH 00/42] nolibc: update to resync with out-of-tree project Paul E. McKenney
2022-02-08 4:41 ` Willy Tarreau
2022-02-08 5:10 ` Paul E. McKenney
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