[libc] Implement strfromd() and strfroml() (#86113)

Follow up to #85438.

Implements the functions `strfromd()` and `strfroml()` introduced in
C23, and unifies the testing framework for `strfrom*()` functions.

libc/config/linux/x86_64/entrypoints.txt

@@ -180,7 +180,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.stdlib.qsort_r
     libc.src.stdlib.rand
     libc.src.stdlib.srand
+    libc.src.stdlib.strfromd
     libc.src.stdlib.strfromf
+    libc.src.stdlib.strfroml
     libc.src.stdlib.strtod
     libc.src.stdlib.strtof
     libc.src.stdlib.strtol

libc/spec/stdc.td

@@ -962,6 +962,8 @@ def StdC : StandardSpec<"stdc"> {
           FunctionSpec<"srand", RetValSpec<VoidType>, [ArgSpec<UnsignedIntType>]>,
 
           FunctionSpec<"strfromf", RetValSpec<IntType>, [ArgSpec<CharRestrictedPtr>, ArgSpec<SizeTType>, ArgSpec<ConstCharRestrictedPtr>, ArgSpec<FloatType>]>,
+          FunctionSpec<"strfromd", RetValSpec<IntType>, [ArgSpec<CharRestrictedPtr>, ArgSpec<SizeTType>, ArgSpec<ConstCharRestrictedPtr>, ArgSpec<DoubleType>]>,
+          FunctionSpec<"strfroml", RetValSpec<IntType>, [ArgSpec<CharRestrictedPtr>, ArgSpec<SizeTType>, ArgSpec<ConstCharRestrictedPtr>, ArgSpec<LongDoubleType>]>,
 
           FunctionSpec<"strtof", RetValSpec<FloatType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>]>,
           FunctionSpec<"strtod", RetValSpec<DoubleType>, [ArgSpec<ConstCharRestrictedPtr>, ArgSpec<CharRestrictedPtrPtr>]>,

libc/src/stdlib/CMakeLists.txt

@@ -62,6 +62,26 @@ add_entrypoint_object(
     .str_from_util
 )
 
+add_entrypoint_object(
+  strfromd
+  SRCS
+    strfromd.cpp
+  HDRS
+    strfromd.h
+  DEPENDS
+    .str_from_util
+)
+
+add_entrypoint_object(
+  strfroml
+  SRCS
+    strfroml.cpp
+  HDRS
+    strfroml.h
+  DEPENDS
+    .str_from_util
+)
+
 add_header_library(
   str_from_util
   HDRS

libc/src/stdlib/strfromd.cpp

@@ -0,0 +1,42 @@
+//===-- Implementation of strfromd ------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdlib/strfromd.h"
+#include "src/stdlib/str_from_util.h"
+
+#include <stdarg.h>
+#include <stddef.h>
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(int, strfromd,
+                   (char *__restrict s, size_t n, const char *__restrict format,
+                    double fp)) {
+  LIBC_ASSERT(s != nullptr);
+
+  printf_core::FormatSection section =
+      internal::parse_format_string(format, fp);
+  printf_core::WriteBuffer wb(s, (n > 0 ? n - 1 : 0));
+  printf_core::Writer writer(&wb);
+
+  int result = 0;
+  if (section.has_conv)
+    result = internal::strfromfloat_convert<double>(&writer, section);
+  else
+    result = writer.write(section.raw_string);
+
+  if (result < 0)
+    return result;
+
+  if (n > 0)
+    wb.buff[wb.buff_cur] = '\0';
+
+  return writer.get_chars_written();
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/stdlib/strfromd.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for strfromd ------------------------*- C++--===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_STRFROMD_H
+#define LLVM_LIBC_SRC_STDLIB_STRFROMD_H
+
+#include <stddef.h>
+
+namespace LIBC_NAMESPACE {
+
+int strfromd(char *__restrict s, size_t n, const char *__restrict format,
+             double fp);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDLIB_STRFROMD_H

libc/src/stdlib/strfromf.h

@@ -18,4 +18,4 @@ int strfromf(char *__restrict s, size_t n, const char *__restrict format,
 
 } // namespace LIBC_NAMESPACE
 
-#endif // LLVM_LIBC_SRC_STDLIB_STRTOF_H
+#endif // LLVM_LIBC_SRC_STDLIB_STRFROMF_H

libc/src/stdlib/strfroml.cpp

@@ -0,0 +1,47 @@
+//===-- Implementation of strfroml ------------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/stdlib/strfroml.h"
+#include "src/stdlib/str_from_util.h"
+
+#include <stdarg.h>
+#include <stddef.h>
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(int, strfroml,
+                   (char *__restrict s, size_t n, const char *__restrict format,
+                    long double fp)) {
+  LIBC_ASSERT(s != nullptr);
+
+  printf_core::FormatSection section =
+      internal::parse_format_string(format, fp);
+
+  // To ensure that the conversion function actually uses long double,
+  // the length modifier has to be set to LenghtModifier::L
+  section.length_modifier = printf_core::LengthModifier::L;
+
+  printf_core::WriteBuffer wb(s, (n > 0 ? n - 1 : 0));
+  printf_core::Writer writer(&wb);
+
+  int result = 0;
+  if (section.has_conv)
+    result = internal::strfromfloat_convert<long double>(&writer, section);
+  else
+    result = writer.write(section.raw_string);
+
+  if (result < 0)
+    return result;
+
+  if (n > 0)
+    wb.buff[wb.buff_cur] = '\0';
+
+  return writer.get_chars_written();
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/stdlib/strfroml.h

@@ -0,0 +1,21 @@
+//===-- Implementation header for strfroml ------------------------*- C++--===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_STDLIB_STRFROML_H
+#define LLVM_LIBC_SRC_STDLIB_STRFROML_H
+
+#include <stddef.h>
+
+namespace LIBC_NAMESPACE {
+
+int strfroml(char *__restrict s, size_t n, const char *__restrict format,
+             long double fp);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_STDLIB_STRFROML_H

libc/test/src/stdlib/CMakeLists.txt

@@ -168,16 +168,47 @@ add_libc_test(
     .strtol_test_support
 )
 
+add_header_library(
+  strfrom_test_support
+  HDRS
+  StrfromTest.h
+  DEPENDS
+  libc.src.__support.CPP.type_traits
+)
+
 add_libc_test(
   strfromf_test
   SUITE
     libc-stdlib-tests
   SRCS
     strfromf_test.cpp
   DEPENDS
+    .strfrom_test_support
     libc.src.stdlib.strfromf
 )
 
+add_libc_test(
+  strfromd_test
+  SUITE
+    libc-stdlib-tests
+  SRCS
+    strfromd_test.cpp
+  DEPENDS
+    .strfrom_test_support
+    libc.src.stdlib.strfromd
+)
+
+add_libc_test(
+  strfroml_test
+  SUITE
+    libc-stdlib-tests
+  SRCS
+    strfroml_test.cpp
+  DEPENDS
+    .strfrom_test_support
+    libc.src.stdlib.strfroml
+)
+
 add_libc_test(
   abs_test
   SUITE