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libstdc++: Fix std::format alternate form for floating-point [PR108046]

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A decimal point was being added to the end of the string for {:#.0}
because the __expc character was not being set, for the _Pres_none
presentation type, so __s.find(__expc) didn't the 'e' in "1e+01" and so
we created "1e+01." by appending the radix char to the end.

This can be fixed by ensuring that __expc='e' is set for the _Pres_none
case. I realized we can also set __expc='P' and __expc='E' when needed,
to save a call to std::toupper later.

For the {:#.0g} format, __expc='e' was being set and so the 'e' was
found in "1e+10" but then __z = __prec - __sigfigs would wraparound to
SIZE_MAX. That meant we would decide not to add a radix char because the
number of extra characters to insert would be 1+SIZE_MAX i.e. zero.

This can be fixed by using __z == 0 when __prec == 0.

libstdc++-v3/ChangeLog:

	PR libstdc++/108046
	* include/std/format (__formatter_fp::format): Ensure __expc is
	always set for all presentation types. Set __z correctly for
	zero precision.
	* testsuite/std/format/functions/format.cc: Check problem cases.
This commit is contained in:
Jonathan Wakely 2023-07-27 14:07:09 +01:00
parent 9bd1ee6d33
commit 50bc490c09
2 changed files with 13 additions and 8 deletions
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17
libstdc++-v3/include/std/format
View file

@ -1430,22 +1430,24 @@ namespace __format
chars_format __fmt{};
bool __upper = false;
bool __trailing_zeros = false;
char __expc = 0;
char __expc = 'e';
switch (_M_spec._M_type)
{
case _Pres_A:
__upper = true;
__expc = 'P';
[[fallthrough]];
case _Pres_a:
__expc = 'p';
if (_M_spec._M_type != _Pres_A)
__expc = 'p';
__fmt = chars_format::hex;
break;
case _Pres_E:
__upper = true;
__expc = 'E';
[[fallthrough]];
case _Pres_e:
__expc = 'e';
__use_prec = true;
__fmt = chars_format::scientific;
break;
@ -1455,10 +1457,10 @@ namespace __format
break;
case _Pres_G:
__upper = true;
__expc = 'E';
[[fallthrough]];
case _Pres_g:
__trailing_zeros = true;
__expc = 'e';
__use_prec = true;
__fmt = chars_format::general;
break;
@ -1511,7 +1513,6 @@ namespace __format
{
for (char* __p = __start; __p != __res.ptr; ++__p)
*__p = std::toupper(*__p);
__expc = std::toupper(__expc);
}
// Add sign for non-negative values.
@ -1545,15 +1546,15 @@ namespace __format
__p = __s.find(__expc);
if (__p == __s.npos)
__p = __s.size();
__d = __p;
__d = __p; // Position where '.' should be inserted.
__sigfigs = __d;
}
if (__trailing_zeros)
if (__trailing_zeros && __prec != 0)
{
if (!__format::__is_xdigit(__s[0]))
--__sigfigs;
__z = __prec - __sigfigs;
__z = __prec - __sigfigs; // Number of zeros to insert.
}
if (size_t __extras = int(__d == __p) + __z)

4
libstdc++-v3/testsuite/std/format/functions/format.cc
View file

@ -152,6 +152,10 @@ test_alternate_forms()
s = std::format("{:#.2g}", -0.0);
VERIFY( s == "-0.0" );
// PR libstdc++/108046
s = std::format("{0:#.0} {0:#.1} {0:#.0g}", 10.0);
VERIFY( s == "1.e+01 1.e+01 1.e+01" );
}
struct euro_punc : std::numpunct<char>