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header.c
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header.c
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#include <stdio.h>
#include <string.h>
#include "header.h"
/* header.c
*
* Processing of compressed file header.
*/
#define HEADER_SIZE (5)
size_t getHeaderSize(void) {
return HEADER_SIZE;
}
void writeHeader(FILE* file,
BlockDescriptor* blockDescriptor) {
char header[HEADER_SIZE] = { 'J', 'L', 'C', 'M', 0 };
header[HEADER_SIZE - 1] = blockDescriptor->encoding;
if (fwrite(header, 1, HEADER_SIZE, file) != HEADER_SIZE) {
error(True, "Unable to write header to output file");
}
}
/* describeCompressionFlags
*
* Describe the file compression.
*
* Parameters:
* Compression flags from header.
*/
static unsigned describeCompressionFlags(unsigned char flags) {
if (flags == 0) {
printf("* File is not compressed\n");
}
else {
if (flags & ENCODING_FLIPPED) printf("* File is flipped\n");
if (flags & ENCODING_RUN_LENGTH) printf("* File is run length encoded\n");
if (flags & ENCODING_HUFFMAN) printf("* File is Huffman encoded\n");
}
return flags;
}
/* getCompressionFlags
*
* Return the compression flags of a file
*
* Parameters:
* filename - input filename
* outputDescription - True if a description of the flags is to be printed
*
* Return:
* Compression flags mask
*/
unsigned char getCompressionFlags(const char* filename,
Boolean outputDescription) {
unsigned char buffer[HEADER_SIZE];
FILE* file = fopen(filename, "rb");
int bytesRead = 0;
const char* expectedHeader = "JLCM";
if (file == NULL) {
error(True, "Unable to open file %s", filename);
}
bytesRead = fread(buffer, 1, sizeof(buffer), file);
if (ferror(file)) {
error(True, "Unable to read file %s", filename);
}
if (fclose(file)) {
error(True, "Unable to close file %s", filename);
}
if (bytesRead < HEADER_SIZE) {
return 0;
}
if (memcmp(buffer, expectedHeader, strlen(expectedHeader))) {
return 0;
}
if (buffer[HEADER_SIZE-1] & (!ENCODING_RUN_LENGTH)) {
error(False,"Looks like a compressed file, but cannot understand encoding\n");
}
return outputDescription ? describeCompressionFlags(buffer[HEADER_SIZE-1]) :
buffer[HEADER_SIZE-1];
}
/* isFlipped
*
* Returns True if the block descriptor indicatates the that file contents
* have been flipped.
*
* Parameters:
* blockDescriptor - descriptor
*
* Return:
* True if the file has been flipped.
*/
Boolean isFlipped(BlockDescriptor* blockDescriptor) {
return (blockDescriptor->encoding & ENCODING_FLIPPED) ? True : False;
}
/* isRleCompressed
*
* Returns True if the block descriptor indicatates the that file contents
* have been run length encoded.
*
* Parameters:
* blockDescriptor - descriptor
*
* Return:
* True if the file has been run length encoded.
*/
Boolean isRleCompressed(BlockDescriptor* blockDescriptor) {
return (blockDescriptor->encoding & ENCODING_RUN_LENGTH) ? True : False;
}
/* isHuffmanCompressed
*
* Returns True if the block descriptor indicatates the that file contents
* have been Huffman encoded.
*
* Parameters:
* blockDescriptor - descriptor
*
* Return:
* True if the file has been Huffman encoded encoded.
*/
Boolean isHuffmanCompressed(BlockDescriptor* blockDescriptor) {
return (blockDescriptor->encoding & ENCODING_HUFFMAN) ? True : False;
}