Improve compression time

tree.c

 
 #include <stdbool.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include "huffman.h"
 #include "tree.h"
@@ -170,15 +171,33 @@ static int get_rev_path(struct tree *parent, unsigned char c, int *buf,
 	return -1;
 }
 
+static int *cpaths[MY_BUF-1];
+static int clengths[MY_BUF-1];
+
 static int write_entry(struct BIT_BUFFER *bitbuf, struct tree *parent,
 					   unsigned char c, int *pathbuf)
 {
-	int length = get_rev_path(parent, c, pathbuf, 0);
+	int length;
+
+	if (cpaths[c]) {
+		pathbuf = cpaths[c];
+		length = clengths[c];
+	}
+	else {
+		length = get_rev_path(parent, c, pathbuf, 0);
+	}
 
 	/* The path is in reverse. Now write it out in correct order. */
 	for (int i = length-1; i >= 0; i--) {
 		bb_write(bitbuf, &pathbuf[i], 1);
 	}
+
+	if (cpaths[c] == NULL) {
+		cpaths[c] = calloc(length, sizeof(int));
+		memcpy(cpaths[c], pathbuf, length * sizeof(int));
+		clengths[c] = length;
+	}
+
 	return 0;
 }
 
@@ -201,6 +220,10 @@ int encode_tree(struct BIT_BUFFER *bitbuf, struct tree *parent, char *buf,
 
 	free(pathbuf);
 
+	for (int i = 0; i < MY_BUF; i++) {
+		free(cpaths[i]);
+	}
+
 	insert_throwaways(bitbuf->fp, 8 - bitbuf->pos);
 
 	return 0;