Initial commit of mktime.

This introduces mktime to LLVM libc, based on C99/C2X/Single Unix Spec.

Co-authored-by: Jeff Bailey <[email protected]>

This change doesn't handle TIMEZONE,  tm_isdst and leap seconds.  It returns -1 for invalid dates. I have verified the return results for all the possible dates with glibc's mktime.

TODO:
+ Handle leap seconds.
+ Handle out of range time and date values that don't overflow or underflow.
+ Implement the following suggestion Siva - As we start accumulating the seconds, we should be able to check if the next amount of seconds to be added can lead to an overflow. If it does, return the overflow value.  If not keep accumulating. The benefit is that, we don't have to validate every input, and also do not need the special cases for sizeof(time_t) == 4.
+ Handle timezone and update of tm_isdst

Reviewed By: sivachandra

Differential Revision: https://reviews.llvm.org/D91551

Author: rtenneti-google

libc/config/linux/api.td

@@ -20,6 +20,28 @@ def SSizeT : TypeDecl<"ssize_t"> {
   }];
 }
 
+def StructTm: TypeDecl<"struct tm"> {
+  let Decl = [{
+    struct tm {
+      int tm_sec; // seconds after the minute
+      int tm_min; // minutes after the hour
+      int tm_hour; // hours since midnight
+      int tm_mday; // day of the month
+      int tm_mon; // months since January
+      int tm_year; // years since 1900
+      int tm_wday; // days since Sunday
+      int tm_yday; // days since January
+      int tm_isdst; // Daylight Saving Time flag
+    };
+  }];
+}
+
+def TimeT: TypeDecl<"time_t"> {
+   let Decl = [{
+   typedef long time_t;
+  }];
+}
+
 def OffT : TypeDecl<"off_t"> {
   let Decl = [{
     #define __need_off_t
@@ -177,6 +199,17 @@ def StdIOAPI : PublicAPI<"stdio.h"> {
 def StdlibAPI : PublicAPI<"stdlib.h"> {
 }
 
+def TimeAPI : PublicAPI<"time.h"> {
+  let TypeDeclarations = [
+    StructTm,
+    TimeT,
+  ];
+
+  let Functions = [
+    "mktime",
+  ];
+}
+
 def ErrnoAPI : PublicAPI<"errno.h"> {
   let Macros = [
     ErrnoMacro,

libc/config/linux/x86_64/entrypoints.txt

@@ -67,6 +67,9 @@ set(TARGET_LIBC_ENTRYPOINTS
     libc.src.threads.thrd_create
     libc.src.threads.thrd_join
 
+    # time.h entrypoints
+    libc.src.time.mktime
+
     # unistd.h entrypoints
     libc.src.unistd.write
 )

libc/config/linux/x86_64/headers.txt

@@ -9,5 +9,6 @@ set(TARGET_PUBLIC_HEADERS
     libc.include.sys_mman
     libc.include.sys_syscall
     libc.include.threads
+    libc.include.time
     libc.include.unistd
 )

libc/include/CMakeLists.txt

@@ -50,6 +50,14 @@ add_gen_header(
     .llvm_libc_common_h
 )
 
+add_gen_header(
+  time
+  DEF_FILE time.h.def
+  GEN_HDR time.h
+  DEPENDS
+    .llvm_libc_common_h
+)
+
 add_gen_header(
   threads
   DEF_FILE threads.h.def

libc/include/time.h.def

@@ -0,0 +1,16 @@
+//===-- C standard library header time.h ----------------------------------===//
+//
+// 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_TIME_H
+#define LLVM_LIBC_TIME_H
+
+#include <__llvm-libc-common.h>
+
+%%public_api()
+
+#endif // LLVM_LIBC_TIME_H

libc/spec/spec.td

@@ -79,6 +79,8 @@ def DoublePtr : PtrType<DoubleType>;
 
 def SigHandlerT : NamedType<"__sighandler_t">;
 
+def TimeTType : NamedType<"time_t">;
+
 //added because __assert_fail needs it.
 def UnsignedType : NamedType<"unsigned">;
 

libc/spec/stdc.td

@@ -3,6 +3,8 @@ def StdC : StandardSpec<"stdc"> {
   NamedType FILE = NamedType<"FILE">;
   PtrType FILEPtr = PtrType<FILE>;
   RestrictedPtrType FILERestrictedPtr = RestrictedPtrType<FILE>;
+  NamedType StructTmType = NamedType<"struct tm">;
+  PtrType StructTmPtr = PtrType<StructTmType>;
 
   HeaderSpec Assert = HeaderSpec<
       "assert.h",
@@ -467,6 +469,23 @@ def StdC : StandardSpec<"stdc"> {
       ]
   >;
 
+  HeaderSpec Time = HeaderSpec<
+      "time.h",
+      [], // Macros
+      [ // Types
+       StructTmType,
+       TimeTType,
+      ],
+      [], // Enumerations
+      [
+          FunctionSpec<
+              "mktime",
+              RetValSpec<TimeTType>,
+              [ArgSpec<StructTmPtr>]
+          >,
+      ]
+  >;
+
   let Headers = [
     Assert,
     CType,
@@ -477,5 +496,6 @@ def StdC : StandardSpec<"stdc"> {
     StdLib,
     Signal,
     Threads,
+    Time,
   ];
 }

libc/src/CMakeLists.txt

@@ -9,6 +9,7 @@ add_subdirectory(string)
 # TODO: Add this target conditional to the target OS.
 add_subdirectory(sys)
 add_subdirectory(threads)
+add_subdirectory(time)
 add_subdirectory(unistd)
 
 add_subdirectory(__support)

libc/src/time/CMakeLists.txt

@@ -0,0 +1,11 @@
+add_entrypoint_object(
+  mktime
+  SRCS
+    mktime.cpp
+  HDRS
+    mktime.h
+  DEPENDS
+    libc.include.errno
+    libc.include.time
+    libc.src.errno.__errno_location
+)

libc/src/time/mktime.cpp

@@ -0,0 +1,126 @@
+//===-- Implementation of mktime function ---------------------------------===//
+//
+// 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 "include/errno.h"
+
+#include "src/__support/common.h"
+#include "src/errno/llvmlibc_errno.h"
+#include "src/time/mktime.h"
+
+namespace __llvm_libc {
+
+constexpr int SecondsPerMin = 60;
+constexpr int MinutesPerHour = 60;
+constexpr int HoursPerDay = 24;
+constexpr int DaysPerWeek = 7;
+constexpr int MonthsPerYear = 12;
+constexpr int DaysPerNonLeapYear = 365;
+constexpr int TimeYearBase = 1900;
+constexpr int EpochYear = 1970;
+constexpr int EpochWeekDay = 4;
+// The latest time that can be represented in this form is 03:14:07 UTC on
+// Tuesday, 19 January 2038 (corresponding to 2,147,483,647 seconds since the
+// start of the epoch). This means that systems using a 32-bit time_t type are
+// susceptible to the Year 2038 problem.
+constexpr int EndOf32BitEpochYear = 2038;
+
+constexpr int NonLeapYearDaysInMonth[] = {31 /* Jan */, 28, 31, 30, 31, 30,
+                                          31,           31, 30, 31, 30, 31};
+
+constexpr bool isLeapYear(const time_t year) {
+  return (((year) % 4) == 0 && (((year) % 100) != 0 || ((year) % 400) == 0));
+}
+
+// POSIX.1-2017 requires this.
+static inline time_t outOfRange() {
+  llvmlibc_errno = EOVERFLOW;
+  return static_cast<time_t>(-1);
+}
+
+time_t LLVM_LIBC_ENTRYPOINT(mktime)(struct tm *t1) {
+  // Unlike most C Library functions, mktime doesn't just die on bad input.
+  // TODO(rtenneti); Handle leap seconds. Handle out of range time and date
+  // values that don't overflow or underflow.
+  // TODO (rtenneti): Implement the following suggestion Siva: "As we start
+  // accumulating the seconds, we should be able to check if the next amount of
+  // seconds to be added can lead to an overflow. If it does, return the
+  // overflow value. If not keep accumulating. The benefit is that, we don't
+  // have to validate every input, and also do not need the special cases for
+  // sizeof(time_t) == 4".
+  if (t1->tm_sec < 0 || t1->tm_sec > (SecondsPerMin - 1))
+    return outOfRange();
+  if (t1->tm_min < 0 || t1->tm_min > (MinutesPerHour - 1))
+    return outOfRange();
+  if (t1->tm_hour < 0 || t1->tm_hour > (HoursPerDay - 1))
+    return outOfRange();
+  time_t tmYearFromBase = t1->tm_year + TimeYearBase;
+
+  if (tmYearFromBase < EpochYear)
+    return outOfRange();
+
+  // 32-bit end-of-the-world is 03:14:07 UTC on 19 January 2038.
+  if (sizeof(time_t) == 4 && tmYearFromBase >= EndOf32BitEpochYear) {
+    if (tmYearFromBase > EndOf32BitEpochYear)
+      return outOfRange();
+    if (t1->tm_mon > 0)
+      return outOfRange();
+    if (t1->tm_mday > 19)
+      return outOfRange();
+    if (t1->tm_hour > 3)
+      return outOfRange();
+    if (t1->tm_min > 14)
+      return outOfRange();
+    if (t1->tm_sec > 7)
+      return outOfRange();
+  }
+
+  // Years are ints.  A 32-bit year will fit into a 64-bit time_t.
+  // A 64-bit year will not.
+  static_assert(sizeof(int) == 4,
+                "ILP64 is unimplemented.  This implementation requires "
+                "32-bit integers.");
+
+  if (t1->tm_mon < 0 || t1->tm_mon > (MonthsPerYear - 1))
+    return outOfRange();
+  bool tmYearIsLeap = isLeapYear(tmYearFromBase);
+  time_t daysInMonth = NonLeapYearDaysInMonth[t1->tm_mon];
+  // Add one day if it is a leap year and the month is February.
+  if (tmYearIsLeap && t1->tm_mon == 1)
+    ++daysInMonth;
+  if (t1->tm_mday < 1 || t1->tm_mday > daysInMonth)
+    return outOfRange();
+
+  time_t totalDays = t1->tm_mday - 1;
+  for (int i = 0; i < t1->tm_mon; ++i)
+    totalDays += NonLeapYearDaysInMonth[i];
+  // Add one day if it is a leap year and the month is after February.
+  if (tmYearIsLeap && t1->tm_mon > 1)
+    totalDays++;
+  t1->tm_yday = totalDays;
+  totalDays += (tmYearFromBase - EpochYear) * DaysPerNonLeapYear;
+
+  // Add an extra day for each leap year, starting with 1972
+  for (time_t year = EpochYear + 2; year < tmYearFromBase;) {
+    if (isLeapYear(year)) {
+      totalDays += 1;
+      year += 4;
+    } else {
+      year++;
+    }
+  }
+
+  t1->tm_wday = (EpochWeekDay + totalDays) % DaysPerWeek;
+  if (t1->tm_wday < 0)
+    t1->tm_wday += DaysPerWeek;
+  // TODO(rtenneti): Need to handle timezone and update of tm_isdst.
+  return t1->tm_sec + t1->tm_min * SecondsPerMin +
+         t1->tm_hour * MinutesPerHour * SecondsPerMin +
+         totalDays * HoursPerDay * MinutesPerHour * SecondsPerMin;
+}
+
+} // namespace __llvm_libc

libc/src/time/mktime.h

@@ -0,0 +1,23 @@
+//===-- Implementation header of mktime -------------------------*- 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_TIME_MKTIME_H
+#define LLVM_LIBC_SRC_TIME_MKTIME_H
+
+#include "src/time/mktime.h"
+#include <time.h>
+
+namespace __llvm_libc {
+
+time_t mktime(struct tm *t1);
+
+} // namespace __llvm_libc
+
+#endif // LLVM_LIBC_SRC_TIME_MKTIME_H
+
+#include "include/time.h"

libc/test/src/CMakeLists.txt

@@ -8,6 +8,7 @@ add_subdirectory(stdlib)
 add_subdirectory(string)
 add_subdirectory(sys)
 add_subdirectory(threads)
+add_subdirectory(time)
 add_subdirectory(unistd)
 
 set(public_test ${CMAKE_CURRENT_BINARY_DIR}/public_integration_test.cpp)

libc/test/src/time/CMakeLists.txt

@@ -0,0 +1,11 @@
+add_libc_testsuite(libc_time_unittests)
+
+add_libc_unittest(
+  mktime
+  SUITE
+    libc_time_unittests
+  SRCS
+    mktime_test.cpp
+  DEPENDS
+    libc.src.time.mktime
+)