decToChar () { # converts single-byte decimal value to equivalent character # arg: decimal number from 0-255 # out: one character echo -n -e "\x$(printf %02X "$1")" } readDecimal() { # Read the n'th decimal from a file. This function looks at the 2 least significant bits of 4 consecutive bytes in # the given file and pastes them together to decode the decimal. # arg1: decimal offset # arg2: filename from which the given decimal should be read and decoded. readcharDec () { # read one character from file & convert to equivalent decimal value # arg1: offset (# of bytes to skip before reading) # arg2: filename # out: decimal value from 0-255 VAL=$(xxd -p -l1 -s $1 $2) printf %d "0x$VAL" } readLSB2 () { # read the 2 LSB's from the byte at the given position in the given file. # arg1: byte offset # arg2: filename READ_BYTE=$(readcharDec $1 $2) echo $(( READ_BYTE & 3 )) } CURRENT_DECIMAL=0 IDX=$1 FILE=$2 for ((j = 3; j > 0; j--)); do CURRENT_VAL=$(readLSB2 $(( IDX * 4 + j )) $FILE) CURRENT_DECIMAL=$(( (CURRENT_DECIMAL | CURRENT_VAL) << 2 )) done CURRENT_VAL=$(readLSB2 $(( IDX * 4 )) $FILE) CURRENT_DECIMAL=$(( (CURRENT_DECIMAL | CURRENT_VAL) )) echo "$CURRENT_DECIMAL" }