On 13/06/19 22:41 +0200, Christophe Lyon wrote:
Hi,
On Wed, 12 Jun 2019 at 16:54, Jonathan Wakely <jwak...@redhat.com> wrote:
The std::to_chars functions from C++17 can be used to implement
std::to_string with much better performance than calling snprintf. Only
the __detail::__to_chars_len and __detail::__to_chars_10 functions are
needed for to_string, because it always outputs base 10 representations.
The return type of __detail::__to_chars_10 should not be declared before
C++17, so the function body is extracted into a new function that can be
reused by to_string and __detail::__to_chars_10.
The existing tests for to_chars rely on to_string to check for correct
answers. Now that they use the same code that doesn't actually ensure
correctness, so add new tests for std::to_string that compare against
printf output.
* include/Makefile.am: Add new <bits/charconv.h> header.
* include/Makefile.in: Regenerate.
* include/bits/basic_string.h (to_string(int), to_string(unsigned))
(to_string(long), to_string(unsigned long), to_string(long long))
(to_string(unsigned long long)): Rewrite to use __to_chars_10_impl.
* include/bits/charconv.h: New header.
(__detail::__to_chars_len): Move here from <charconv>.
(__detail::__to_chars_10_impl): New function extracted from
__detail::__to_chars_10.
* include/std/charconv (__cpp_lib_to_chars): Add, but comment out.
(__to_chars_unsigned_type): New class template that reuses
__make_unsigned_selector_base::__select to pick a type.
(__unsigned_least_t): Redefine as __to_chars_unsigned_type<T>::type.
(__detail::__to_chars_len): Move to new header.
(__detail::__to_chars_10): Add inline specifier. Move code doing the
output to __detail::__to_chars_10_impl and call that.
* include/std/version (__cpp_lib_to_chars): Add, but comment out.
* testsuite/21_strings/basic_string/numeric_conversions/char/
to_string.cc: Fix reference in comment. Remove unused variable.
* testsuite/21_strings/basic_string/numeric_conversions/char/
to_string_int.cc: New test.
Tested x86_64-linux, committed to trunk.
The new test to_string_int.cc fails on arm-none-eabi:
PASS: 21_strings/basic_string/numeric_conversions/char/to_string_int.cc
(test for excess errors)
spawn
/aci-gcc-fsf/builds/gcc-fsf-gccsrc/obj-arm-none-eabi/gcc3/utils/bin/qemu-wrapper.sh
./to_string_int.exe
/libstdc++-v3/testsuite/21_strings/basic_string/numeric_conversions/char/to_string_int.cc:105:
void check_value(T) [with T = long long int]: Assertion 's ==
expected' failed.
FAIL: 21_strings/basic_string/numeric_conversions/char/to_string_int.cc
execution test
Does the target support "%lld" in printf?
Does the .sum file show UNSUPPORTED for the existing
21_strings/basic_string/numeric_conversions/char/to_string.cc test?
Does the attached patch make the test show what fails?
I suspect the problem is that the test relies on snprintf to check the
answers are correct, even though the actual library code doesn't need
snprintf any longer. Previously the std::to_string functions were all
guarded by _GLIBCXX_USE_C99_STDIO and so I'm guessing were not
supported for arm-none-eabi. Now the overloads for integral types
should work without any C library support, and so the new test is
enabled unconditionally. But the test itself still uses the C library.
Maybe I should have a simple test that doesn't use snprintf and just
checks some hardcoded values produce the expected results, and a more
involved test that compares the results to snprintf but uses
{ dg-require-string-conversions "" } like the existing test.
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/numeric_conversions/char/to_string_int.cc b/libstdc++-v3/testsuite/21_strings/basic_string/numeric_conversions/char/to_string_int.cc
index 8eb2a48bd30..911e6812b39 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/numeric_conversions/char/to_string_int.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/numeric_conversions/char/to_string_int.cc
@@ -95,13 +95,15 @@ const std::uint_least32_t values[] = {
const std::size_t empty_string_capacity = std::string().capacity();
-#include <set>
+#include <iostream>
template<typename T>
void check_value(T val)
{
const std::string s = std::to_string(val);
const std::string expected = test::to_string(val);
+ if (s != expected)
+ std::cerr << "GOT: " << s << " BUT EXPECTED: " << expected << '\n';
VERIFY( s == expected );
VERIFY( s[s.size()] == '\0' ); // null-terminator not overwritten!
if (s.size() > empty_string_capacity)
