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Merge pull request #395 from sahvx655-wq/is-space-signed-compare

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guard is_space against negative signed code units
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Daniel Lemire 2026-06-18 16:33:25 -04:00 committed by GitHub
commit 8ec5d236e2
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2 changed files with 31 additions and 2 deletions
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6
include/fast_float/float_common.h
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@ -1223,7 +1223,11 @@ template <typename T> constexpr bool space_lut<T>::value[];
#endif #endif
template <typename UC> constexpr bool is_space(UC c) { template <typename UC> constexpr bool is_space(UC c) {
return c < 256 && space_lut<>::value[uint8_t(c)]; // wchar_t and char can be signed, so a negative code unit slips past a plain
// `c < 256` and then indexes the table by its truncated low byte. Compare as
// unsigned, matching the care taken in ch_to_digit.
using UnsignedUC = typename std::make_unsigned<UC>::type;
return static_cast<UnsignedUC>(c) < 256 && space_lut<>::value[uint8_t(c)];
} }
template <typename UC> static constexpr uint64_t int_cmp_zeros() { template <typename UC> static constexpr uint64_t int_cmp_zeros() {

27
tests/wide_char_test.cpp
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@ -2,6 +2,7 @@
#include <iostream> #include <iostream>
#include <string> #include <string>
#include <system_error> #include <system_error>
#include <type_traits>
bool tester(std::string s, double expected, bool tester(std::string s, double expected,
fast_float::chars_format fmt = fast_float::chars_format::general) { fast_float::chars_format fmt = fast_float::chars_format::general) {
@ -46,8 +47,32 @@ bool test_nan() {
return tester("nan", std::numeric_limits<double>::quiet_NaN()); return tester("nan", std::numeric_limits<double>::quiet_NaN());
} }
// A wide code unit whose low byte is an ASCII space (0x20) but whose full value
// is not whitespace must not be skipped by skip_white_space. When wchar_t is
// signed such a unit can be negative, which used to slip past the range guard
// in is_space and get treated as a space.
bool test_non_space_with_space_low_byte() {
if (!std::is_signed<wchar_t>::value) {
return true; // only reproducible where wchar_t is signed
}
std::wstring input = L" 42";
// 0x...FF20: low byte 0x20, high bits set, so the value is negative.
input[0] = static_cast<wchar_t>(~static_cast<unsigned int>(0xFF) | 0x20u);
double result;
auto answer =
fast_float::from_chars(input.data(), input.data() + input.size(), result,
fast_float::chars_format::general |
fast_float::chars_format::skip_white_space);
if (answer.ec == std::errc()) {
std::cerr << "leading non-space code unit must not be skipped\n";
return false;
}
return true;
}
int main() { int main() {
if (test_minus() && test_plus() && test_space() && test_nan()) { if (test_minus() && test_plus() && test_space() && test_nan() &&
test_non_space_with_space_low_byte()) {
std::cout << "all ok" << std::endl; std::cout << "all ok" << std::endl;
return EXIT_SUCCESS; return EXIT_SUCCESS;
} }