[libc] add snprintf

[michaelrj]

Summary

After adding sprintf, snprintf is simple. The functions are very
similar. The tests only cover the behavior of the max length since the
sprintf tests should cover the other behavior.

[lntue]

libc/src/stdio/snprintf.cpp

27

nit: *handling*

[michaelrj]

fix typo

libc/config/linux/x86_64/entrypoints.txt

list(APPEND TARGET_LIBC_ENTRYPOINTS
     libc.src.stdio.fopencookie
     libc.src.stdio.fread
     libc.src.stdio.fread_unlocked
     libc.src.stdio.fseek
     libc.src.stdio.funlockfile
     libc.src.stdio.fwrite
     libc.src.stdio.fwrite_unlocked
     libc.src.stdio.sprintf
+    libc.src.stdio.snprintf
 
     # signal.h entrypoints
     # TODO: Enable signal.h entrypoints after fixing signal.h
     # libc.src.signal.raise
     # libc.src.signal.sigaction
     # libc.src.signal.sigdelset
     # libc.src.signal.sigaddset
     # libc.src.signal.sigemptyset

libc/spec/stdc.td

HeaderSpec StdIO = HeaderSpec<
           >,
           FunctionSpec<
               "sprintf",
               RetValSpec<IntType>,
               [ArgSpec<CharRestrictedPtr>,
                ArgSpec<ConstCharRestrictedPtr>,
                ArgSpec<VarArgType>]
           >,
+          FunctionSpec<
+              "snprintf",
+              RetValSpec<IntType>,
+              [ArgSpec<CharRestrictedPtr>,
+               ArgSpec<SizeTType>,
+               ArgSpec<ConstCharRestrictedPtr>,
+               ArgSpec<VarArgType>]
+          >,
+          FunctionSpec<
+              "printf",
+              RetValSpec<IntType>,
+              [ArgSpec<ConstCharRestrictedPtr>,
+               ArgSpec<VarArgType>]
+          >,
+          FunctionSpec<
+              "fprintf",
+              RetValSpec<IntType>,
+              [ArgSpec<FILERestrictedPtr>,
+               ArgSpec<ConstCharRestrictedPtr>,
+               ArgSpec<VarArgType>]
+          >,
       ]
   >;
 
   HeaderSpec StdLib = HeaderSpec<
       "stdlib.h",
       [], // Macros
       [
           DivTType,

libc/src/stdio/CMakeLists.txt

 
 add_entrypoint_object(
   sprintf
   SRCS
     sprintf.cpp
   HDRS
     sprintf.h
   DEPENDS
-    libc.include.stdio
+    libc.src.stdio.printf_core.printf_main
+    libc.src.stdio.printf_core.string_writer
+    libc.src.stdio.printf_core.writer
+)
+
+add_entrypoint_object(
+  snprintf
+  SRCS
+    snprintf.cpp
+  HDRS
+    snprintf.h
+  DEPENDS
     libc.src.stdio.printf_core.printf_main
     libc.src.stdio.printf_core.string_writer
     libc.src.stdio.printf_core.writer
 )

libc/src/stdio/snprintf.h

+//===-- Implementation header of snprintf -----------------------*- 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_STDIO_SNPRINTF_H
+#define LLVM_LIBC_SRC_STDIO_SNPRINTF_H
+
+#include <stddef.h>
+
+namespace __llvm_libc {
+
+int snprintf(char *__restrict buffer, size_t buffsz,
+             const char *__restrict format, ...);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_STDIO_SNPRINTF_H

libc/src/stdio/snprintf.cpp

-//===-- Implementation of sprintf -------------------------------*- C++ -*-===//
+//===-- Implementation of snprintf ------------------------------*- 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/stdio/sprintf.h"
+#include "src/stdio/snprintf.h"
 
 #include "src/__support/arg_list.h"
 #include "src/stdio/printf_core/printf_main.h"
 #include "src/stdio/printf_core/string_writer.h"
 #include "src/stdio/printf_core/writer.h"
 
 #include <stdarg.h>
+#include <stddef.h>
 
 namespace __llvm_libc {
 
-LLVM_LIBC_FUNCTION(int, sprintf,
-                   (char *__restrict buffer, const char *__restrict format,
-                    ...)) {
+LLVM_LIBC_FUNCTION(int, snprintf,
+                   (char *__restrict buffer, size_t buffsz,
+                    const char *__restrict format, ...)) {
   va_list vlist;
   va_start(vlist, format);
   internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handing
+                                 // and pointer semantics, as well as handling
                                  // destruction automatically.
   va_end(vlist);
-  printf_core::StringWriter str_writer(buffer);
+  printf_core::StringWriter str_writer(buffer, (buffsz > 0 ? buffsz - 1 : 0));
   printf_core::Writer writer(reinterpret_cast<void *>(&str_writer),
                              printf_core::write_to_string);
 
   int ret_val = printf_core::printf_main(&writer, format, args);
+  if (buffsz > 0) // if the buffsz is 0 the buffer may be a null pointer.
     str_writer.terminate();
   return ret_val;
 }
 
 } // namespace __llvm_libc

libc/src/stdio/sprintf.cpp

 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sprintf,
                    (char *__restrict buffer, const char *__restrict format,
                     ...)) {
   va_list vlist;
   va_start(vlist, format);
   internal::ArgList args(vlist); // This holder class allows for easier copying
-                                 // and pointer semantics, as well as handing
+                                 // and pointer semantics, as well as handling
                                  // destruction automatically.
   va_end(vlist);
   printf_core::StringWriter str_writer(buffer);
   printf_core::Writer writer(reinterpret_cast<void *>(&str_writer),
                              printf_core::write_to_string);
 
   int ret_val = printf_core::printf_main(&writer, format, args);
   str_writer.terminate();
   return ret_val;
 }
 
 } // namespace __llvm_libc

libc/test/src/stdio/CMakeLists.txt

add_libc_unittest(
   SUITE
     libc_stdio_unittests
   SRCS
     sprintf_test.cpp
   DEPENDS
     libc.src.stdio.sprintf
 )
 
+add_libc_unittest(
+  snprintf_test
+  SUITE
+    libc_stdio_unittests
+  SRCS
+    snprintf_test.cpp
+  DEPENDS
+    libc.src.stdio.snprintf
+)
+
 add_subdirectory(printf_core)
 
 add_subdirectory(testdata)

libc/test/src/stdio/snprintf_test.cpp

+//===-- Unittests for snprintf --------------------------------------------===//
+//
+// 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/stdio/snprintf.h"
+
+#include "utils/UnitTest/Test.h"
+
+// The sprintf test cases cover testing the shared printf functionality, so
+// these tests will focus on snprintf exclusive features.
+
+TEST(LlvmLibcSNPrintfTest, CutOff) {
+  char buff[64];
+  int written;
+
+  written =
+      __llvm_libc::snprintf(buff, 16, "A simple string with no conversions.");
+  EXPECT_EQ(written, 36);
+  ASSERT_STREQ(buff, "A simple string");
+
+  written = __llvm_libc::snprintf(buff, 5, "%s", "1234567890");
+  EXPECT_EQ(written, 10);
+  ASSERT_STREQ(buff, "1234");
+
+  // passing null as the output pointer is allowed as long as buffsz is 0.
+  written = __llvm_libc::snprintf(nullptr, 0, "%s and more", "1234567890");
+  EXPECT_EQ(written, 19);
+}
+
+TEST(LlvmLibcSNPrintfTest, NoCutOff) {
+  char buff[64];
+  int written;
+
+  written =
+      __llvm_libc::snprintf(buff, 37, "A simple string with no conversions.");
+  EXPECT_EQ(written, 36);
+  ASSERT_STREQ(buff, "A simple string with no conversions.");
+
+  written = __llvm_libc::snprintf(buff, 20, "%s", "1234567890");
+  EXPECT_EQ(written, 10);
+  ASSERT_STREQ(buff, "1234567890");
+}