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tools/nolibc/printf: Simplify __nolibc_printf()

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Move the check for the length modifiers into the format processing
between the field width and conversion specifier.
This lets the loop be simplified and a 'fast scan' for a format start
used.

If an error is detected (eg an invalid conversion specifier) then
copy the invalid format to the output buffer.

Reduces code size by about 10% on x86-64.

Some versions of gcc bloat this version by generating a jump table.
All goes away in the later patches.

Signed-off-by: David Laight <david.laight.linux@gmail.com>
Acked-by: Willy Tarreau <w@1wt.eu>
Link: https://patch.msgid.link/20260308113742.12649-7-david.laight.linux@gmail.com
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
This commit is contained in:
David Laight 2026-03-08 11:37:31 +00:00 committed by Thomas Weißschuh
parent a2fa5a752c
commit b3d30efd05
1 changed files with 54 additions and 52 deletions
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106
tools/include/nolibc/stdio.h
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@ -310,28 +310,52 @@ typedef int (*__nolibc_printf_cb)(void *state, const char *buf, size_t size);
static __attribute__((unused, format(printf, 3, 0)))
int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list args)
{
char escape, lpref, ch;
char lpref, ch;
unsigned long long v;
int written, width, len;
size_t ofs;
char outbuf[21];
const char *outstr;
written = ofs = escape = lpref = 0;
written = 0;
while (1) {
ch = fmt[ofs++];
width = 0;
outstr = fmt;
ch = *fmt++;
if (!ch)
break;
if (escape) {
/* we're in an escape sequence, ofs == 1 */
escape = 0;
width = 0;
if (ch != '%') {
while (*fmt && *fmt != '%')
fmt++;
/* Output characters from the format string. */
len = fmt - outstr;
} else {
/* we're in a format sequence */
ch = *fmt++;
/* width */
while (ch >= '0' && ch <= '9') {
width *= 10;
width += ch - '0';
ch = fmt[ofs++];
ch = *fmt++;
}
/* Length modifiers */
if (ch == 'l') {
lpref = 1;
ch = *fmt++;
if (ch == 'l') {
lpref = 2;
ch = *fmt++;
}
} else if (ch == 'j') {
/* intmax_t is long long */
lpref = 2;
ch = *fmt++;
} else {
lpref = 0;
}
if (ch == 'c' || ch == 'd' || ch == 'u' || ch == 'x' || ch == 'p') {
@ -387,56 +411,34 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
#else
outstr = strerror(errno);
#endif /* NOLIBC_IGNORE_ERRNO */
}
else if (ch == '%') {
/* queue it verbatim */
continue;
}
else {
/* modifiers or final 0 */
if (ch == 'l') {
/* long format prefix, maintain the escape */
lpref++;
} else if (ch == 'j') {
lpref = 2;
} else {
if (ch != '%') {
/* Invalid format: back up to output the format characters */
fmt = outstr + 1;
/* and output a '%' now. */
}
escape = 1;
goto do_escape;
/* %% is documented as a 'conversion specifier'.
* Any flags, precision or length modifier are ignored.
*/
width = 0;
outstr = "%";
}
len = strlen(outstr);
goto flush_str;
}
/* not an escape sequence */
if (ch == 0 || ch == '%') {
/* flush pending data on escape or end */
escape = 1;
lpref = 0;
outstr = fmt;
len = ofs - 1;
flush_str:
width -= len;
while (width > 0) {
/* Output pad in 16 byte blocks with the small block first. */
int pad_len = ((width - 1) & 15) + 1;
width -= pad_len;
written += pad_len;
if (cb(state, " ", pad_len) != 0)
return -1;
}
if (cb(state, outstr, len) != 0)
written += len;
width -= len;
while (width > 0) {
/* Output pad in 16 byte blocks with the small block first. */
int pad_len = ((width - 1) & 15) + 1;
width -= pad_len;
written += pad_len;
if (cb(state, " ", pad_len) != 0)
return -1;
written += len;
do_escape:
if (ch == 0)
break;
fmt += ofs;
ofs = 0;
continue;
}
/* literal char, just queue it */
if (cb(state, outstr, len) != 0)
return -1;
}
/* Request a final '\0' be added to the snprintf() output.