kopia lustrzana https://github.com/DL7AD/pecanpico9
127 wiersze
4.7 KiB
Python
127 wiersze
4.7 KiB
Python
# Copyright 2013-2016 Alex Danilo
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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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#
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# Base 128/192 encoding experiment.
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#
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# Ths is just a quick experiment to see what sort of speed we get by encoding
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# a contiguous 128 value range in bytes that replaces base 64 with it's low level
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# conditionals and bit-bashing for decode.
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#
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# Ultimately, the encoding I'd like to use is a 192 value encoding which yields
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# 7.5 bits/byte - i.e. approx. 6.66% loss encoding binary data in a text-safe
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# transfer form. The 128 value coding is just to test the basis of the
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# speed and compressibility of the result and is easy to use in JS. The 192
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# value encoding is more efficient but likely a lot trickier to use from JS.
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#
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# NB: This is using ISO-9959-1 as it's basis. The source code will break if you
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# try to view as UTF-8.
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# The decode table reverses the encoding back to bits. Note, that since the most we can encode is 7.5 bits, we can never
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# generate 0xFF in the decode so use that to mark 0xFF encoding bytes.
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import struct
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dtab = [
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 187, 0xFF, 188, 0xFF, 0xFF, 0xFF, 0xFF,
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 189, 190, 0xFF, 0xFF, 0xFF,
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191, 0xFE, 0xFF, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
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13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
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29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44,
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45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 0xFF, 57, 58, 59,
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60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75,
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76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 0xFF,
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
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91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106,
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107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122,
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123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138,
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139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154,
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155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170,
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171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186
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]
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# Reserve " (0x3E) as delimiter for easy manipulation in JS, '!' as stuffing character and generation for JS - the ranges 23->7E then A0->FF create the encoding.
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# That's enough for the base 128 version but we need 4 more characters to encode 7.5 bits/byte so the last set is carefully chosen from within
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# the control character range using values that are safe for editors.
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etab = "#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_`abcdefghijklmnopqrstuvwxyz{|}~\xA0\xA1\xA2\xA3\xA4\xA5\xA6\xA7\xA8\xA9\xAA\xAB\xAC\xAD\xAE\xAF\xB0\xB1\xB2\xB3\xB4\xB5\xB6\xB7\xB8\xB9\xBA\xBB\xBC\xBD\xBE\xBF\xC0\xC1\xC2\xC3\xC4\xC5\xC6\xC7\xC8\xC9\xCA\xCB\xCC\xCD\xCE\xCF\xD0\xD1\xD2\xD3\xD4\xD5\xD6\xD7\xD8\xD9\xDA\xDB\xDC\xDD\xDE\xDF\xE0\xE1\xE2\xE3\xE4\xE5\xE6\xE7\xE8\xE9\xEA\xEB\xEC\xED\xEE\xEF\xF0\xF1\xF2\xF3\xF4\xF5\xF6\xF7\xF8\xF9\xFA\xFB\xFC\xFD\xFE\xFF\t\x0B\x1B\x1C ";
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INBYTES = 7
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OUTBYTES = 8
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def encode(infile):
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outfile = ''
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k = 0
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while k < len(infile):
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_len = 0
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_in = []
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for i in range(INBYTES):
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_in.append(infile[k])
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k += 1
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_len += 1
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if k >= len(infile):
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break
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if _len > 0:
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topbits = 0
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mask = 0x40
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for i in range(_len):
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outfile += etab[_in[i] & 0x7F]
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if _in[i] > 0x7F:
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topbits |= mask
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mask >>= 1
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if _len < INBYTES:
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outfile += '!'
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outfile += etab[topbits]
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return outfile
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def decode(infile):
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out = bytearray()
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k = 0
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while k < len(infile):
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_len = 0
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_in = []
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for i in range(OUTBYTES):
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_in.append(ord(infile[k]))
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k += 1
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_len += 1;
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if k >= len(infile):
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break
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if _len > 0:
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topbits = dtab[_in[_len - 1]]
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mask = 0x40
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_len = 0
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for i in range(len(_in)-1):
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if _in[i] == 0x21:
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break
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_len += 1
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_in[i] = dtab[_in[i]]
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if _in[i] == 0xFF:
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return 0
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if topbits & mask:
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_in[i] |= 0x80
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mask >>= 1
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for i in range(_len):
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out += struct.pack('B', _in[i])
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return out
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