38 lines
1.2 KiB
Go
38 lines
1.2 KiB
Go
// Copyright 2012 Aaron Jacobs. All Rights Reserved.
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// Author: aaronjjacobs@gmail.com (Aaron Jacobs)
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package common
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// ShiftLeft shifts the binary string left by one bit, causing the
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// most-signficant bit to disappear and a zero to be introduced at the right.
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// This corresponds to the `x << 1` notation of RFC 4493.
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func ShiftLeft(b []byte) []byte {
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l := len(b)
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if l == 0 {
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panic("shiftLeft requires a non-empty buffer.")
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}
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output := make([]byte, l)
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overflow := byte(0)
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for i := int(l - 1); i >= 0; i-- {
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output[i] = b[i] << 1
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output[i] |= overflow
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overflow = (b[i] & 0x80) >> 7
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}
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return output
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}
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