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tools/nolibc/stdlib: replace the ltoa() function with more efficient ones

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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>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Willy Tarreau 2022-02-07 17:23:27 +01:00 committed by Paul E. McKenney
parent 56d68a3c1f
commit 66c397c4d2
1 changed files with 87 additions and 20 deletions
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107
tools/include/nolibc/stdlib.h
View file

@ -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))