================
@@ -53,24 +56,150 @@ _LIBCPP_BEGIN_NAMESPACE_STD
namespace __format {
+// A helper to limit the total size of code units written.
+class _LIBCPP_HIDE_FROM_ABI __max_output_size {
+public:
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI explicit __max_output_size(size_t
__max_size) : __max_size_{__max_size} {}
+
+ // This function adjusts the size of a (bulk) write operations. It ensures
the
+ // number of code units written by a __output_buffer never exceeds
+ // __max_size_ code units.
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI size_t __write_request(size_t
__code_units) {
+ size_t __result =
+ __code_units_written_ < __max_size_ ? std::min(__code_units,
__max_size_ - __code_units_written_) : 0;
+ __code_units_written_ += __code_units;
+ return __result;
+ }
+
+ [[nodiscard]] _LIBCPP_HIDE_FROM_ABI size_t __code_units_written() const
noexcept { return __code_units_written_; }
+
+private:
+ size_t __max_size_;
+ // The code units that would have been written if there was no limit.
+ // format_to_n returns this value.
+ size_t __code_units_written_{0};
+};
+
/// A "buffer" that handles writing to the proper iterator.
///
/// This helper is used together with the @ref back_insert_iterator to offer
/// type-erasure for the formatting functions. This reduces the number to
/// template instantiations.
+///
+/// The design is the following:
+/// - There is an external object that connects the buffer to the output.
+/// - This buffer object:
+/// - inherits publicly from this class.
+/// - has a static or dynamic buffer.
+/// - has a static member function to make space in its buffer write
+/// operations. This can be done by increasing the size of the internal
+/// buffer or by writing the contents of the buffer to the output iterator.
+///
+/// This member function is a constructor argument, so its name is not
+/// fixed. The code uses the name __prepare_write.
+/// - The number of output code units can be limited by a __max_output_size
+/// object. This is used in format_to_n This object:
+/// - Contains the maximum number of code units to be written.
+/// - Contains the number of code units that are requested to be written.
+/// This number is returned to the user of format_to_n.
+/// - The write functions call the object's __request_write member function.
+/// This function:
+/// - Updates the number of code units that are requested to be written.
+/// - Returns the number of code units that can be written without
+/// exceeding the maximum number of code units to be written.
+///
+/// Documentation for the buffer usage members:
+/// - __ptr_
+/// The start of the buffer.
+/// - __capacity_
+/// The number of code units that can be written. This means
+/// [__ptr_, __ptr_ + __capacity_) is a valid range to write to.
+/// - __size_
+/// The number of code units written in the buffer. The next code unit will
+/// be written at __ptr_ + __size_. This __size_ may NOT contain the total
+/// number of code units written by the __output_buffer. Whether or not it
+/// does depends on the sub-class used. Typically the total number of code
+/// units written is not interesting. It is interesting for format_to_n which
+/// has its own way to track this number.
+///
+/// Documentation for the buffer modifying buffer operations:
----------------
ldionne wrote:
```suggestion
/// Documentation for the modifying buffer operations:
```
https://github.com/llvm/llvm-project/pull/108990
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