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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#include "runtime.h"
#include "os_GOOS.h"
int64
runtime·nanotime(void)
{
static int32 fd = -1;
byte b[8];
uint32 hi, lo;
// As long as all goroutines share the same file
// descriptor table we can get away with using
// just a static fd. Without a lock the file can
// be opened twice but that's okay.
//
// Using /dev/bintime gives us a latency on the
// order of ten microseconds between two calls.
//
// The naïve implementation (without the cached
// file descriptor) is roughly four times slower
// in 9vx on a 2.16 GHz Intel Core 2 Duo.
if(fd < 0 && (fd = runtime·open("/dev/bintime", OREAD|OCEXEC, 0)) < 0)
return 0;
if(runtime·pread(fd, b, sizeof b, 0) != sizeof b)
return 0;
hi = b[0]<<24 | b[1]<<16 | b[2]<<8 | b[3];
lo = b[4]<<24 | b[5]<<16 | b[6]<<8 | b[7];
return (int64)hi<<32 | (int64)lo;
}
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