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vsprintf: deal with format flags with a simple lookup table

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Rather than a case statement, just look up the printf format flags
(justification, zero-padding etc) using a small table.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2024-12-19 10:02:45 -08:00
parent 938df695e9
commit 312f48b2e2
1 changed files with 21 additions and 20 deletions
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41
lib/vsprintf.c
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@ -2527,6 +2527,20 @@ struct fmt {
enum format_state state;
};
#define SPEC_CHAR(x, flag) [(x)-32] = flag
static unsigned char spec_flag(unsigned char c)
{
static const unsigned char spec_flag_array[] = {
SPEC_CHAR(' ', SPACE),
SPEC_CHAR('#', SPECIAL),
SPEC_CHAR('+', PLUS),
SPEC_CHAR('-', LEFT),
SPEC_CHAR('0', ZEROPAD),
};
c -= 32;
return (c < sizeof(spec_flag_array)) ? spec_flag_array[c] : 0;
}
/*
* Helper function to decode printf style format.
* Each call decode a token from the format and return the
@ -2552,7 +2566,7 @@ static noinline_for_stack
struct fmt format_decode(struct fmt fmt, struct printf_spec *spec)
{
const char *start = fmt.str;
char qualifier;
char flag, qualifier;
/* we finished early by reading the field width */
if (fmt.state == FORMAT_STATE_WIDTH) {
@ -2585,26 +2599,13 @@ struct fmt format_decode(struct fmt fmt, struct printf_spec *spec)
if (fmt.str != start || !*fmt.str)
return fmt;
/* Process flags */
/* Process flags. This also skips the first '%' */
spec->flags = 0;
while (1) { /* this also skips first '%' */
bool found = true;
fmt.str++;
switch (*fmt.str) {
case '-': spec->flags |= LEFT; break;
case '+': spec->flags |= PLUS; break;
case ' ': spec->flags |= SPACE; break;
case '#': spec->flags |= SPECIAL; break;
case '0': spec->flags |= ZEROPAD; break;
default: found = false;
}
if (!found)
break;
}
do {
/* this also skips first '%' */
flag = spec_flag(*++fmt.str);
spec->flags |= flag;
} while (flag);
/* get field width */
spec->field_width = -1;