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