python实现算术编码
时间: 2023-07-11 07:04:25 浏览: 92
算术编码是一种基于符号概率的数据压缩方法,可以将任意消息编码为一个实数,这个实数可以被解码回原始消息。下面是Python实现的算术编码示例代码:
```python
from decimal import Decimal
def arithmetic_encode(data, freqs):
low = Decimal(0)
high = Decimal(1)
range_size = Decimal(1)
for symbol in data:
sym_low, sym_high = freqs[symbol]
sym_range = sym_high - sym_low
low += range_size * sym_low
high = low + range_size * sym_range
range_size *= sym_range
return (low + high) / 2
def arithmetic_decode(encoded_data, freqs, length):
result = []
low = Decimal(0)
high = Decimal(1)
range_size = Decimal(1)
code = Decimal(encoded_data)
for i in range(length):
for symbol, (sym_low, sym_high) in freqs.items():
sym_range = sym_high - sym_low
if low + range_size * sym_low <= code < low + range_size * sym_high:
result.append(symbol)
high = low + range_size * sym_high
low += range_size * sym_low
range_size *= sym_range
break
return result
```
在这个代码中,`arithmetic_encode` 函数将输入数据 `data` 压缩为一个实数,并返回该实数。`freqs` 是一个字典,其中包含每个符号及其出现频率的信息。`arithmetic_decode` 函数将压缩后的数据解码回原始数据。
下面是一个使用示例:
```python
data = "hello world"
freqs = {"h": (0, 0.1), "e": (0.1, 0.2), "l": (0.2, 0.5), "o": (0.5, 0.6), " ": (0.6, 0.7), "w": (0.7, 0.8), "r": (0.8, 0.9), "d": (0.9, 1.0)}
encoded = arithmetic_encode(data, freqs)
print("Encoded data:", encoded)
decoded = arithmetic_decode(encoded, freqs, len(data))
print("Decoded data:", "".join(decoded))
```
这个示例中,我们将字符串 "hello world" 压缩,并将每个字符的频率作为字典传递给 `arithmetic_encode` 函数。我们打印出压缩后的数据和解压缩后的数据。