[libc-commits] [libc] [libc]: Implement strfrom* functions and utils (PR #85438)

[Michael Jones via libc-commits]

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@@ -0,0 +1,134 @@
+//===-- Implementation header for strfromx() utilitites -------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// According to the C23 standard, any input character sequences except a
+// precision specifier and the usual floating point formats, namely
+// %{a,A,e,E,f,F,g,G}, are not allowed and any code that does otherwise results
+// in undefined behaviour(including use of a '%%' conversion specifier); which
+// in this case is that the buffer string is simply populated with the format
+// string. The case of the value of buffer size being 0 or the input being NULL
+// should be handled in the calling function (strfromf, strfromd, strfroml)
+// itself.
+
+#ifndef LLVM_LIBC_SRC_STDLIB_STRFROM_UTIL_H
+#define LLVM_LIBC_SRC_STDLIB_STRFROM_UTIL_H
+
+#include "src/__support/CPP/type_traits.h"
+#include "src/__support/str_to_integer.h"
+#include "src/stdio/printf_core/converter_atlas.h"
+#include "src/stdio/printf_core/core_structs.h"
+#include "src/stdio/printf_core/writer.h"
+
+#include <stddef.h>
+
+namespace LIBC_NAMESPACE::internal {
+
+template <typename T>
+using storage_type = typename fputil::FPBits<T>::StorageType;
+
+template <typename T>
+printf_core::FormatSection parse_format_string(const char *__restrict format,
+                                               T fp) {
+  printf_core::FormatSection section;
+  size_t cur_pos = 0;
+  [[maybe_unused]] double new_fp;
+
+  bool t_is_single_prec_type = cpp::is_same<T, float>::value;
+  if (t_is_single_prec_type)
+    new_fp = (double)fp;
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michaelrj-google wrote:

add a comment explaining why this is necessary

https://github.com/llvm/llvm-project/pull/85438