extents-intersection

#!/bin/bash

# SPDX-FileCopyrightText: 2016-2020 Graham R. Cobb
# SPDX-License-Identifier: GPL-3.0-or-later
#
# Copyright (C) 2016 Graham R. Cobb
# Released under GPL V3.0 -- see LICENSE
#
# extents-intersection [-s] <filename>...
#
#
# Output the extents contained in all of the named extents lists
#
# Note: uses file descriptors 7 and 8
#

if [ "$1" = "-s" ]
then
    shift
    $0 "$@" | extents-size
    exit $?
fi

if [ $# -lt 2 ]
then
    echo "Usage: $0 <filename> <filename>..." >&2
    exit 1
fi

intersect2() {
    # File descriptors
    IN1=7
    IN2=8
    exec 7<$1 8<$2

    read -u $IN1 start1 end1 restofline || return
    read -u $IN2 start2 end2 restofline || return
    if [ -z "$start1" -o -z "$start2" -o -z "$end1" -o -z "$end2" ] ; then return ; fi

    while true
    do
	#    echo "Outer loop: S1=$start1 E1=$end1 S2=$start2 E2=$end2"
	
	while [ $start1 -gt $end2 -o $start2 -gt $end1 ]
	do
	    #	echo "Inner loop: S1=$start1 E1=$end1 S2=$start2 E2=$end2"
	    # Skip forward file 2 until it overlaps with extent1
	    while [ $start1 -gt $end2 ]
	    do read -u $IN2 start2 end2 restofline && [ -n "$start2" ] && [ -n "$end2" ] || return
	    done

	    # Skip forward file 1 until it overlaps with extent2
	    while [ $start2 -gt $end1 ]
	    do read -u $IN1 start1 end1 restofline && [ -n "$start1" ] && [ -n "$end1" ] || return
	    done
	done

	# We have an overlap
	#    echo "Overlap: S1=$start1 E1=$end1 S2=$start2 E2=$end2"
	
	# Move to start of overlap
	if [ $start1 -lt $start2 ] ; then start1=$start2 ; fi
	if [ $start2 -lt $start1 ] ; then start2=$start1 ; fi

	# Find end of overlap
	if [ $end1 -lt $end2 ] ; then end=$end1 ; else end=$end2 ; fi

	# Got overlap
	let length=$end-$start1+1
	echo $start1 $end $length

	# Move on...
	let start1=$end+1
	let start2=$end+1
    done
}

if [ $# -eq 2 ]
then intersect2 "$@"
else
    file1=$1
    file2=$2
    shift 2
    outfile="$(mktemp)"
    intersect2 $file1 $file2 >$outfile
    $0 $outfile "$@"
    rm $outfile
fi