1//===-- Baremetal implementation of the clock function --------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "src/time/clock.h"
10#include "hdr/time_macros.h"
11#include "hdr/types/struct_timespec.h"
12#include "src/__support/CPP/limits.h"
13#include "src/__support/common.h"
14#include "src/__support/macros/config.h"
15#include "src/__support/time/units.h"
16
17namespace LIBC_NAMESPACE_DECL {
18
19extern "C" bool __llvm_libc_timespec_get_active(struct timespec *ts);
20
21LLVM_LIBC_FUNCTION(clock_t, clock, ()) {
22 using namespace time_units;
23 struct timespec ts;
24 if (!__llvm_libc_timespec_get_active(&ts))
25 return clock_t(-1);
26
27 // The above call gets the CPU time in seconds plus nanoseconds.
28 // The standard requires that we return clock_t(-1) if we cannot represent
29 // clocks as a clock_t value.
30 constexpr clock_t CLOCK_SECS_MAX =
31 cpp::numeric_limits<clock_t>::max() / CLOCKS_PER_SEC;
32 if (ts.tv_sec > CLOCK_SECS_MAX)
33 return clock_t(-1);
34 if (ts.tv_nsec / 1_s_ns > CLOCK_SECS_MAX - ts.tv_sec)
35 return clock_t(-1);
36
37 // For the integer computation converting tv_nsec to clocks to work
38 // correctly, we want CLOCKS_PER_SEC to be less than 1000000000.
39 static_assert(1_s_ns > CLOCKS_PER_SEC,
40 "Expected CLOCKS_PER_SEC to be less than 1'000'000'000.");
41 return clock_t(ts.tv_sec * CLOCKS_PER_SEC +
42 ts.tv_nsec / (1_s_ns / CLOCKS_PER_SEC));
43}
44
45} // namespace LIBC_NAMESPACE_DECL
46

source code of libc/src/time/baremetal/clock.cpp