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ergo/vendor/github.com/GehirnInc/crypt/common/base64.go
2020-10-02 16:48:37 -04:00

60 lines
1.5 KiB
Go

// (C) Copyright 2012, Jeramey Crawford <jeramey@antihe.ro>. All
// rights reserved. Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package common
const (
alphabet = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
)
// Base64_24Bit is a variant of Base64 encoding, commonly used with password
// hashing algorithms to encode the result of their checksum output.
//
// The algorithm operates on up to 3 bytes at a time, encoding the following
// 6-bit sequences into up to 4 hash64 ASCII bytes.
//
// 1. Bottom 6 bits of the first byte
// 2. Top 2 bits of the first byte, and bottom 4 bits of the second byte.
// 3. Top 4 bits of the second byte, and bottom 2 bits of the third byte.
// 4. Top 6 bits of the third byte.
//
// This encoding method does not emit padding bytes as Base64 does.
func Base64_24Bit(src []byte) []byte {
if len(src) == 0 {
return []byte{} // TODO: return nil
}
dstlen := (len(src)*8 + 5) / 6
dst := make([]byte, dstlen)
di, si := 0, 0
n := len(src) / 3 * 3
for si < n {
val := uint(src[si+2])<<16 | uint(src[si+1])<<8 | uint(src[si])
dst[di+0] = alphabet[val&0x3f]
dst[di+1] = alphabet[val>>6&0x3f]
dst[di+2] = alphabet[val>>12&0x3f]
dst[di+3] = alphabet[val>>18]
di += 4
si += 3
}
rem := len(src) - si
if rem == 0 {
return dst
}
val := uint(src[si+0])
if rem == 2 {
val |= uint(src[si+1]) << 8
}
dst[di+0] = alphabet[val&0x3f]
dst[di+1] = alphabet[val>>6&0x3f]
if rem == 2 {
dst[di+2] = alphabet[val>>12]
}
return dst
}