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[libc] Fix incorrect printing for alt mode ints #70252

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Merged
merged 1 commit into from
Oct 27, 2023
Merged

[libc] Fix incorrect printing for alt mode ints #70252

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16 changes: 14 additions & 2 deletions libc/src/stdio/printf_core/int_converter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -113,7 +113,7 @@ LIBC_INLINE int convert_int(Writer *writer, const FormatSection &to_conv) {
size_t prefix_len;
char prefix[2];
if ((to_lower(to_conv.conv_name) == 'x') &&
((flags & FormatFlags::ALTERNATE_FORM) != 0)) {
((flags & FormatFlags::ALTERNATE_FORM) != 0) && num != 0) {
prefix_len = 2;
prefix[0] = '0';
prefix[1] = a + ('x' - 'a');
Expand Down Expand Up @@ -158,8 +158,20 @@ LIBC_INLINE int convert_int(Writer *writer, const FormatSection &to_conv) {
prefix_len);
}

// The standard says that alternate form for the o conversion "increases
// the precision, if and only if necessary, to force the first digit of the
// result to be a zero (if the value and precision are both 0, a single 0 is
// printed)"
// This if checks the following conditions:
// 1) is this an o conversion in alternate form?
// 2) does this number has a leading zero?
// 2a) ... because there are additional leading zeroes?
// 2b) ... because it is just "0", unless it will not write any digits.
const bool has_leading_zero =
(zeroes > 0) || ((num == 0) && (digits_written != 0));
if ((to_conv.conv_name == 'o') &&
((to_conv.flags & FormatFlags::ALTERNATE_FORM) != 0) && zeroes < 1) {
((to_conv.flags & FormatFlags::ALTERNATE_FORM) != 0) &&
!has_leading_zero) {
zeroes = 1;
--spaces;
}
Expand Down
16 changes: 16 additions & 0 deletions libc/test/src/stdio/sprintf_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -329,6 +329,10 @@ TEST(LlvmLibcSPrintfTest, HexConv) {
EXPECT_EQ(written, 5);
ASSERT_STREQ(buff, "0xd3f");

written = LIBC_NAMESPACE::sprintf(buff, "%#x", 0);
EXPECT_EQ(written, 1);
ASSERT_STREQ(buff, "0");

written = LIBC_NAMESPACE::sprintf(buff, "%#X", 0xE40);
EXPECT_EQ(written, 5);
ASSERT_STREQ(buff, "0XE40");
Expand Down Expand Up @@ -359,6 +363,10 @@ TEST(LlvmLibcSPrintfTest, HexConv) {
EXPECT_EQ(written, 9);
ASSERT_STREQ(buff, " 0X009D4");

written = LIBC_NAMESPACE::sprintf(buff, "%#.x", 0);
EXPECT_EQ(written, 0);
ASSERT_STREQ(buff, "");

written = LIBC_NAMESPACE::sprintf(buff, "%-7.5x", 0x260);
EXPECT_EQ(written, 7);
ASSERT_STREQ(buff, "00260 ");
Expand Down Expand Up @@ -516,6 +524,10 @@ TEST(LlvmLibcSPrintfTest, OctConv) {
EXPECT_EQ(written, 4);
ASSERT_STREQ(buff, "0234");

written = LIBC_NAMESPACE::sprintf(buff, "%#o", 0);
EXPECT_EQ(written, 1);
ASSERT_STREQ(buff, "0");

written = LIBC_NAMESPACE::sprintf(buff, "%05o", 0470);
EXPECT_EQ(written, 5);
ASSERT_STREQ(buff, "00470");
Expand All @@ -534,6 +546,10 @@ TEST(LlvmLibcSPrintfTest, OctConv) {
EXPECT_EQ(written, 7);
ASSERT_STREQ(buff, "0703 ");

written = LIBC_NAMESPACE::sprintf(buff, "%#.o", 0);
EXPECT_EQ(written, 1);
ASSERT_STREQ(buff, "0");

written = LIBC_NAMESPACE::sprintf(buff, "%7.5o", 0314);
EXPECT_EQ(written, 7);
ASSERT_STREQ(buff, " 00314");
Expand Down