1 //===-- Linux 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 "src/__support/CPP/limits.h" 12 #include "src/__support/common.h" 13 #include "src/__support/time/linux/clock_gettime.h" 14 #include "src/__support/time/units.h" 15 #include "src/errno/libc_errno.h" 16 17 namespace LIBC_NAMESPACE { 18 19 LLVM_LIBC_FUNCTION(clock_t, clock, ()) { 20 using namespace time_units; 21 struct timespec ts; 22 auto result = internal::clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts); 23 if (!result.has_value()) { 24 libc_errno = result.error(); 25 return -1; 26 } 27 28 // The above syscall gets the CPU time in seconds plus nanoseconds. 29 // The standard requires that we return clock_t(-1) if we cannot represent 30 // clocks as a clock_t value. 31 constexpr clock_t CLOCK_SECS_MAX = 32 cpp::numeric_limits<clock_t>::max() / CLOCKS_PER_SEC; 33 if (ts.tv_sec > CLOCK_SECS_MAX) 34 return clock_t(-1); 35 if (ts.tv_nsec / 1_s_ns > CLOCK_SECS_MAX - ts.tv_sec) 36 return clock_t(-1); 37 38 // For the integer computation converting tv_nsec to clocks to work 39 // correctly, we want CLOCKS_PER_SEC to be less than 1000000000. 40 static_assert(1_s_ns > CLOCKS_PER_SEC, 41 "Expected CLOCKS_PER_SEC to be less than 1'000'000'000."); 42 return clock_t(ts.tv_sec * CLOCKS_PER_SEC + 43 ts.tv_nsec / (1_s_ns / CLOCKS_PER_SEC)); 44 } 45 46 } // namespace LIBC_NAMESPACE 47