[libcxx-commits] [PATCH] D99091: [locale][num_get] Improve Stage 2 of string to float conversion

[Tomas Matheson via Phabricator via libcxx-commits]

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https://timsong-cpp.github.io/cppwp/n4140/facet.num.get.virtuals#3.2

"Stage 2" of num_get::do_get() depends on "a check ... to determine if c is
allowed as the next character of an input field of the conversion specifier
returned by Stage 1". Previously this was a very simple check whether the next
character was in a set of allowed characters.  This could lead to Stage 2
accumulating character sequences such as "1.2f" and passing them to strtold
(Stage 3).
https://timsong-cpp.github.io/cppwp/n4140/facet.num.get.virtuals#3.3.3

Stage 3 can fail, however, if the entire character sequence from Stage 2 is not
used in the conversion. For example, the "f" in "1.2f" is not used.
https://timsong-cpp.github.io/cppwp/n4140/facet.num.get.virtuals#3.3.4

As a result, parsing a sequence like "1.2f" would return value 0.0 with failbit
set.

This change improves the checks made in Stage 2, determining what is passed to
Stage 3.

- Hex digits are only considered valid if "0x" has been seen

- INFINITY value is recognised

- Characters in INFINITY and NAN are only valid in sequence. This is done by checking one character backwards, which has obvious limitations.

- New tests are added. The old ones are preserved but refactored.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D99091

Files:
  libcxx/include/locale
  libcxx/src/locale.cpp
  libcxx/test/std/localization/locale.categories/category.numeric/locale.num.get/facet.num.get.members/get_float.pass.cpp

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