50 lines
956 B
Go
50 lines
956 B
Go
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package internal
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import "unsafe"
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const wordSize = int(unsafe.Sizeof(uintptr(0)))
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func maskBytes(key [4]byte, pos int, b []byte) int {
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// Mask one byte at a time for small buffers.
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if len(b) < 2*wordSize {
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for i := range b {
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b[i] ^= key[pos&3]
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pos++
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}
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return pos & 3
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}
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// Mask one byte at a time to word boundary.
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if n := int(uintptr(unsafe.Pointer(&b[0]))) % wordSize; n != 0 {
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n = wordSize - n
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for i := range b[:n] {
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b[i] ^= key[pos&3]
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pos++
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}
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b = b[n:]
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}
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// Create aligned word size key.
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var k [wordSize]byte
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for i := range k {
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k[i] = key[(pos+i)&3]
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}
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kw := *(*uintptr)(unsafe.Pointer(&k))
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// Mask one word at a time.
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n := (len(b) / wordSize) * wordSize
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for i := 0; i < n; i += wordSize {
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*(*uintptr)(unsafe.Pointer(uintptr(unsafe.Pointer(&b[0])) + uintptr(i))) ^= kw
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}
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// Mask one byte at a time for remaining bytes.
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b = b[n:]
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for i := range b {
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b[i] ^= key[pos&3]
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pos++
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}
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return pos & 3
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}
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