mirror of https://github.com/docker/cli.git
47 lines
1.4 KiB
Go
47 lines
1.4 KiB
Go
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// +build !appengine
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// This file encapsulates usage of unsafe.
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// xxhash_safe.go contains the safe implementations.
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package xxhash
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import (
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"reflect"
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"unsafe"
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)
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// Notes:
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//
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// See https://groups.google.com/d/msg/golang-nuts/dcjzJy-bSpw/tcZYBzQqAQAJ
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// for some discussion about these unsafe conversions.
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//
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// In the future it's possible that compiler optimizations will make these
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// unsafe operations unnecessary: https://golang.org/issue/2205.
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//
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// Both of these wrapper functions still incur function call overhead since they
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// will not be inlined. We could write Go/asm copies of Sum64 and Digest.Write
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// for strings to squeeze out a bit more speed. Mid-stack inlining should
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// eventually fix this.
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// Sum64String computes the 64-bit xxHash digest of s.
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// It may be faster than Sum64([]byte(s)) by avoiding a copy.
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func Sum64String(s string) uint64 {
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var b []byte
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bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
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bh.Data = (*reflect.StringHeader)(unsafe.Pointer(&s)).Data
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bh.Len = len(s)
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bh.Cap = len(s)
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return Sum64(b)
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}
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// WriteString adds more data to d. It always returns len(s), nil.
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// It may be faster than Write([]byte(s)) by avoiding a copy.
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func (d *Digest) WriteString(s string) (n int, err error) {
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var b []byte
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bh := (*reflect.SliceHeader)(unsafe.Pointer(&b))
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bh.Data = (*reflect.StringHeader)(unsafe.Pointer(&s)).Data
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bh.Len = len(s)
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bh.Cap = len(s)
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return d.Write(b)
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}
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