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ungz

This is a little modified source code from an excellent article "Dissecting the GZIP format" by Joshua Davies.

Modifications

Modifications include:

  • Convert to C99 and apply more compact code style
  • Fix one bug related to building of dynamic Huffman trees
  • Add workaround to support files greater than 32k

Difference from gunzip

gunzip handles various compatibility issues, does compression, is written in old school C (and sometimes in asm!) and optimized. All this compilcates its source code. For example, it builds and uses multi-level lookup tables where ungz just traverse binary tree in several lines of code.

Tests

Tested with this bash command

find / -maxdepth 6 -name "*.gz" -size 1M -readable -exec test.sh {} \;  2>&1 | grep -v "Permission denied"

and this script

#!/bin/bash
ungz "$*" > /tmp/ungz.out
gunzip "$*" -c > /tmp/gunzip.out
DIFF=$(diff /tmp/ungz.out /tmp/gunzip.out)
if [ "$DIFF" != "" ]
then
    echo "----------------------------------------"
    echo "$*"
    diff /tmp/ungz.out /tmp/gunzip.out | head -n 10
fi

on about 10 000 files.