[PATCH v3 next 13/17] tools/nolibc/printf: Add support for conversion flags
From: david . laight . linux
Date: Mon Feb 23 2026 - 05:35:56 EST
From: David Laight <david.laight.linux@xxxxxxxxx>
Add support for:
'+' and ' ' Sign characters for non-negative numbers.
'#' adds 0x to hex numbers.
outputting "(nil)" for NULL pointers.
Special code for 0 is needed because "%#x" needs to generate "0" not "0x0".
The code is changed to use the length returned by u64toh_r() and
prepend the sign (or "0x") after conversion to reduce the changes for
the next patch that inserts zero padding between the sign and digits.
Add tests for "%#x", "% d", "%+d" and passing NULL to "%p".
Signed-off-by: David Laight <david.laight.linux@xxxxxxxxx>
---
Changes for v3:
- Was patch 7 in v2.
- Changes for left alignment moved to the next patch.
- Rename 'sign' 'sign_prefix'.
- Include tests
Changes for v2:
- Add support for left justifying fields (removed from patch 6).
- Merge in the changes from the old patch 8.
- Add support for "%#x" (formally part of patch 9).
tools/include/nolibc/stdio.h | 68 +++++++++++++++-----
tools/testing/selftests/nolibc/nolibc-test.c | 3 +
2 files changed, 55 insertions(+), 16 deletions(-)
diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h
index 6dd27473ab7f..c21abe085fa6 100644
--- a/tools/include/nolibc/stdio.h
+++ b/tools/include/nolibc/stdio.h
@@ -296,7 +296,7 @@ int fseek(FILE *stream, long offset, int whence)
* - %% generates a single %
* - %m outputs strerror(errno).
* - %X outputs a..f the same as %x.
- * - The modifiers [#-+ 0] are currently ignored.
+ * - The modifiers [-0] are currently ignored.
* - No support for precision or variable widths.
* - No support for floating point or wide characters.
* - Invalid formats are copied to the output buffer.
@@ -345,9 +345,10 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
long long signed_v;
int written, width, len;
unsigned int flags, ch_flag;
- char outbuf[21];
+ char outbuf[2 + 22 + 1];
char *out;
const char *outstr;
+ unsigned int sign_prefix;
written = 0;
while (1) {
@@ -409,8 +410,11 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
* so that 'X' can be allowed through.
* 'X' gets treated and 'x' because _NOLIBC_PF_FLAG() returns the same
* value for both.
+ *
+ * We need to check for "%p" or "%#x" later, merging here gives better code.
+ * But '#' collides with 'c' so shift right.
*/
- ch_flag = _NOLIBC_PF_FLAG(ch);
+ ch_flag = _NOLIBC_PF_FLAG(ch) | (flags & _NOLIBC_PF_FLAG('#')) >> 1;
if (((ch >= 'a' && ch <= 'z') || ch == 'X') &&
_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'c', 'd', 'i', 'u', 'x', 'p', 's')) {
/* 'long' is needed for pointer/string conversions and ltz lengths.
@@ -446,32 +450,64 @@ int __nolibc_printf(__nolibc_printf_cb cb, void *state, const char *fmt, va_list
goto do_strlen_output;
}
- out = outbuf;
+ /* The 'sign_prefix' can be zero, one or two ("0x") characters. */
+ sign_prefix = 0;
if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'd', 'i')) {
/* "%d" and "%i" - signed decimal numbers. */
if (signed_v < 0) {
- *out++ = '-';
+ sign_prefix = '-';
v = -(signed_v + 1);
v++;
+ } else if (_NOLIBC_PF_FLAGS_CONTAIN(flags, '+')) {
+ sign_prefix = '+';
+ } else if (_NOLIBC_PF_FLAGS_CONTAIN(flags, ' ')) {
+ sign_prefix = ' ';
}
}
- /* Convert the number to ascii in the required base. */
- if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'd', 'i', 'u')) {
- /* Base 10 */
- u64toa_r(v, out);
- } else {
- /* Base 16 */
+ /* The value is converted offset into the buffer so that
+ * the sign/prefix can be added in front.
+ * The longest digit string is 22 + 1 for octal conversions, the
+ * space is reserved even though octal isn't currently supported.
+ */
+ out = outbuf + 2;
+
+ if (v == 0) {
+ /* There are special rules for zero. */
if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'p')) {
- *(out++) = '0';
- *(out++) = 'x';
+ /* "%p" match glibc, precision is ignored */
+ outstr = "(nil)";
+ len = 5;
+ goto do_output;
+ }
+ /* All other formats (including "%#x") just output "0". */
+ out[0] = '0';
+ len = 1;
+ } else {
+ /* Convert the number to ascii in the required base. */
+ if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'd', 'i', 'u')) {
+ /* Base 10 */
+ len = u64toa_r(v, out);
+ } else {
+ /* Base 16 */
+ if (_NOLIBC_PF_FLAGS_CONTAIN(ch_flag, 'p', '#' - 1)) {
+ /* "%p" and "%#x" need "0x" prepending. */
+ sign_prefix = 'x' | '0' << 8;
+ }
+ len = u64toh_r(v, out);
}
- u64toh_r(v, out);
}
- outstr = outbuf;
- goto do_strlen_output;
+ /* Add the 0, 1 or 2 ("0x") sign/prefix characters at the front. */
+ for (; sign_prefix; sign_prefix >>= 8) {
+ /* Force gcc to increment len inside the loop. */
+ _NOLIBC_OPTIMIZER_HIDE_VAR(len);
+ len++;
+ *--out = sign_prefix;
+ }
+ outstr = out;
+ goto do_output;
}
if (ch == 'm') {
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 498d3125eb24..f746711af777 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1832,6 +1832,7 @@ static int run_printf(int min, int max)
CASE_TEST(string); EXPECT_VFPRINTF(1, "foo", "%s", "foo"); break;
CASE_TEST(number); EXPECT_VFPRINTF(1, "1234", "%d", 1234); break;
CASE_TEST(negnumber); EXPECT_VFPRINTF(1, "-1234", "%d", -1234); break;
+ CASE_TEST(num_sign); EXPECT_VFPRINTF(1, "| 1|+2|+3|+4|5|", "|% d|%+d|% +d|%+ d|%#d|", 1, 2, 3, 4, 5); break;
CASE_TEST(unsigned); EXPECT_VFPRINTF(1, "12345", "%u", 12345); break;
CASE_TEST(signed_max); EXPECT_VFPRINTF(1, "2147483647", "%i", ~0u >> 1); break;
CASE_TEST(signed_min); EXPECT_VFPRINTF(1, "-2147483648", "%i", (~0u >> 1) + 1); break;
@@ -1840,6 +1841,7 @@ static int run_printf(int min, int max)
CASE_TEST(hex_nolibc); EXPECT_VFPRINTF(is_nolibc, "|f|d|", "|%x|%X|", 0xf, 0xd); break;
CASE_TEST(hex_libc); EXPECT_VFPRINTF(!is_nolibc, "|f|D|", "|%x|%X|", 0xf, 0xd); break;
CASE_TEST(pointer); EXPECT_VFPRINTF(1, "0x1", "%p", (void *) 0x1); break;
+ CASE_TEST(pointer_NULL); EXPECT_VFPRINTF(1, "(nil)", "%p", (void *)0); break;
CASE_TEST(percent); EXPECT_VFPRINTF(1, "a%d42%69%", "a%%d%d%%%d%%", 42, 69); break;
CASE_TEST(perc_qual); EXPECT_VFPRINTF(1, "a%d2", "a%-14l%d%d", 2); break;
CASE_TEST(invalid); EXPECT_VFPRINTF(1, "a%12yx3%y42%P", "a%12yx%d%y%d%P", 3, 42); break;
@@ -1850,6 +1852,7 @@ static int run_printf(int min, int max)
CASE_TEST(string_width); EXPECT_VFPRINTF(1, " 1", "%10s", "1"); break;
CASE_TEST(number_width); EXPECT_VFPRINTF(1, " 1", "%10d", 1); break;
CASE_TEST(width_trunc); EXPECT_VFPRINTF(1, " 1", "%30d", 1); break;
+ CASE_TEST(hex_alt); EXPECT_VFPRINTF(1, "|0x1| 0x2| 0|", "|%#x|%#5x|%#5x|", 1, 2, 0); break;
CASE_TEST(errno); EXPECT_VFPRINTF(is_nolibc, "22:errno=22", "%d:%m", errno=22); break;
CASE_TEST(errno-neg); EXPECT_VFPRINTF(is_nolibc, "-22: errno=-22", "%d:%12m", errno=-22); break;
CASE_TEST(scanf); EXPECT_ZR(1, test_scanf()); break;
--
2.39.5