Create huffman_compress.cpp

compresses files

Author: shivamgupta1

huffman_compress.cpp

@@ -0,0 +1,137 @@
+/*
+*NO Error checking or handling whatsoever in this code
+*use at your own risk
+*@author shivam gupta
+*/
+
+#include <cstdio>
+#include <iostream>
+#include <algorithm>
+#include <queue>
+#include <string>
+
+#define OUT_OF_RANGE 256         //256 is out of range of a byte and is used in place of null
+
+using namespace std;
+
+struct treeNode {
+    int ch;
+    long long int freq;
+    treeNode *left, *right;
+    treeNode(int c, long long int f, treeNode *l, treeNode *r) : ch(c),freq(f),left(l),right(r) {}
+    treeNode(const treeNode &t) : ch(t.ch), freq(t.freq),left(t.left),right(t.right) {}
+    bool operator< (const treeNode &rhs) const {
+        return this->freq > rhs.freq;
+	}
+};
+
+void codegenerator(treeNode *root, string &s, vector<string> &code) {
+    if(!root) {
+        return;
+    }
+    if(root->ch != OUT_OF_RANGE) { // ch not null
+        code[root->ch] = s;
+        cout << root->ch << " " << s<< endl;
+    }
+    s.push_back('0');
+    codegenerator(root->left, s, code);
+    s.erase(s.end()-1);
+    s.push_back('1');
+    codegenerator(root->right, s, code);
+    s.erase(s.end()-1);
+}
+
+class BitWriter {
+	int bit_counter;        //how many bits in current byte
+	unsigned char curr_byte;  //curr_byte to write later
+	FILE *fp;
+public:
+	BitWriter(FILE *f) : bit_counter(0), curr_byte(0), fp(f) {}
+	void write(unsigned char bit) {
+		curr_byte <<= 1;
+		curr_byte |= bit;
+		if(++bit_counter == 8) {
+			fwrite(&curr_byte, 1, 1, fp);
+			bit_counter = 0;
+			curr_byte = 0;
+		}
+	}
+	void flush() {       //used to flush last byte
+        if(bit_counter>0) {
+            fwrite(&curr_byte, 1,1 ,fp);
+        }
+	}
+};
+
+int main() {
+	FILE *inp = fopen("binary_file.jpg", "rb");
+	FILE *out = fopen("compressed.myformat", "wb");
+
+    vector<long long int> freq_store(256, 0);
+    vector<string> code(256);
+    vector<int> store;
+
+	unsigned char buffer[1];
+	while(fread(buffer, 1, 1, inp)>0) {  //arguments : character address to read to, size(in bytes) of each element to read, number of such elements to read, file desc
+        if(freq_store[(int)buffer[0]] == 0 ) { //storing all the bytes present to push into queue later
+            store.push_back((int)buffer[0]);
+        }
+		freq_store[(int)buffer[0]]++;
+	}
+	rewind(inp);
+
+	for(int i = 0; i<store.size(); i++) {
+        cout << store[i] << " " << freq_store[store[i]] << endl;
+	}
+
+    priority_queue<treeNode> pq;
+    for(int i = 0; i<store.size(); i++) {  //pushing all the stored bytes into the priority queue
+        pq.push(treeNode(store[i], freq_store[(int)store[i]], NULL, NULL));
+    }
+
+    treeNode *root;
+
+    while(pq.size() > 1) { //need to extract 2 elements
+        treeNode t1 = pq.top();
+        pq.pop();
+        treeNode t2 = pq.top();
+        pq.pop();
+
+        treeNode *l = new treeNode(t1);
+        treeNode *r = new treeNode(t2);
+
+        root = new treeNode(OUT_OF_RANGE, l->freq+r->freq, l, r);
+
+        pq.push(*root);
+    }
+
+    string s = "";
+    codegenerator(root, s, code);
+
+    for(int i = 0; i<store.size(); i++) {  //all this is stored as text, so each character takes 1 byte, which is too much space(5-6 KB max)
+        fprintf(out, "%s %d ", code[store[i]].c_str(), store[i]);
+	}
+	fprintf(out, "| ");
+
+	long long int bitStreamLength = 0;  // after | store the bit stream length in the file itself
+	while(fread(buffer, 1, 1, inp)>0) {
+		bitStreamLength += code[(int)buffer[0]].length();
+	}
+	rewind(inp);
+
+	fprintf(out, " %lld ", bitStreamLength); //actually printing the size of the bit stream to the file, binary data starts immediately after |
+
+	BitWriter bw(out);
+
+	while(fread(buffer, 1, 1, inp) > 0) {
+		string cd = code[(int)buffer[0]];
+		for(int i = 0; i<cd.length(); i++) {
+			bw.write(cd[i]-'0');        //gives 0 or 1 integer value to write function instead of chars '0' or '1'
+		}
+	}
+	rewind(inp);
+
+    bw.flush(); //write any remaining bits in buffer
+
+    return 0;
+}