计算文件的熵 [英] Calculate entropy of a file
本文介绍了计算文件的熵的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我已经尝试从Google,论坛,维基百科和许多很多论坛中搜索此功能超过两个小时,但我找不到它.我该怎么做?我尝试了以下操作,但是没有用.
I have tried to search this function for over two hours from google, forums, wikipedia and many, many forums but I couldn't find it. How I can do this? I tried the following but it didn't work.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <stdint.h>
static unsigned int mylog2 (unsigned int val) {
unsigned int ret = -1;
while (val != 0) {
val >>= 1;
ret++;
}
return ret;
}
int main(int argc, char **argv)
{
FILE *pFile;
int i; // various loop index
int j; // filename loop index
int n; // Bytes read by fread;
int size; // Filesize
float entropy;
float temp; // temp value used in entropy calculation
long alphabet[256];
unsigned char buffer[1024];
/* do this for all files */
for(j = 1; j < argc; j++)
{
/* initialize all values */
size = 0;
entropy = 0.0;
memset(alphabet, 0, sizeof(long) * 256);
pFile = fopen(argv[j], "rb");
if(pFile == NULL)
{
printf("Failed to open `%s`\n", argv[j]);
continue;
}
/* Read the whole file in parts of 1024 */
while((n = fread(buffer, 1, 1024, pFile)) != 0)
{
/* Add the buffer to the alphabet */
for (i = 0; i < n; i++)
{
alphabet[(int) buffer[i]]++;
size++;
}
}
fclose(pFile);
/* entropy calculation */
for (i = 0; i < 256; i++)
{
if (alphabet[i] != 0)
{
temp = (float) alphabet[i] / (float) size;
entropy += -temp * mylog2(temp);
}
}
printf("%02.5f [ %02.5f ]\t%s\n", entropy, entropy / 8, argv[j]);
} // outer for
return 0;
}
我知道我做错了.在python中,这似乎要容易得多,在python中,它是:
I know I am doing it wrong. In python it's seems to be a lot easier, in python it is:
import sys
import math
if len(sys.argv) != 2:
print "Usage: file_entropy.py [path]filename"
sys.exit()
# read the whole file into a byte array
f = open(sys.argv[1], "rb")
byteArr = map(ord, f.read())
f.close()
fileSize = len(byteArr)
print 'File size in bytes:'
print fileSize
print
# calculate the frequency of each byte value in the file
freqList = []
for b in range(256):
ctr = 0
for byte in byteArr:
if byte == b:
ctr += 1
freqList.append(float(ctr) / fileSize)
# print 'Frequencies of each byte-character:'
# print freqList
# print
# Shannon entropy
ent = 0.0
for freq in freqList:
if freq > 0:
ent = ent + freq * math.log(freq, 2)
ent = -ent
print 'Shannon entropy (min bits per byte-character):'
print ent
print
print 'Min possible file size assuming max theoretical compression efficiency:'
print (ent * fileSize), 'in bits'
print (ent * fileSize) / 8, 'in bytes'
### Modifications to file_entropy.py to create the Histogram start here ###
### by Ken Hartman www.KennethGHartman.com
import numpy as np
import matplotlib.pyplot as plt
N = len(freqList)
ind = np.arange(N) # the x locations for the groups
width = 1.00 # the width of the bars
#fig = plt.figure()
fig = plt.figure(figsize=(11,5),dpi=100)
ax = fig.add_subplot(111)
rects1 = ax.bar(ind, freqList, width)
ax.set_autoscalex_on(False)
ax.set_xlim([0,255])
ax.set_ylabel('Frequency')
ax.set_xlabel('Byte')
ax.set_title('Frequency of Bytes 0 to 255\nFILENAME: ' + sys.argv[1])
plt.show()
如何在C ++中实现相同的目标?希望有人能回答事实.
How to achieve the same in C++ ? Hopefully somebody answers factually.
推荐答案
您不得以2为底计算对数的整数部分.要在C中以base2为底计算对数,可以使用以下命令中的 log2
math.h
.
You must not compute the integral part of the logarithm in base 2. To compute logarithm in base2 in C you can use log2
from math.h
.
这篇关于计算文件的熵的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文