It pads with a fixed byte. You could always download it and check the source:
Code:
/* find the amount the file has over the limit */
fseek(fp, 0, SEEK_END);
overage = ftell(fp) % factor;
if(overage != 0)
{
unsigned long extension = factor - overage;
while(extension >= 1024)
{
fwrite(zeroz, 1, 1024, fp);
extension -= 1024;
}
if(extension >= 0)
{
fwrite(zeroz, 1, extension, fp);
}
}
A 1024 byte buffer called 'zeroz' gets written multiple times to the file. The compiler fills it with the value 0x00, but you can modify the source code to fill 'zeroz' with any other constant byte (such as 0xFF) before it gets to this part.