#!/bin/bash
########
#Brute force searches for the CHS geometry that can best utilize a
#device with a given total sector count.  For each cylinder count,
#starting with the minimum possible and continuing until the
#cylinder size is reduced to just 8 sectors, it finds the best H
#and S count.  A line is written st stdout each time a geometry is
#found that is at least as good as the best one seen so far.
#(Sometimes a later geometry that yields the same sector count is
#in some way "nicer".)
#
#The "-d" option adjusts the calculation to account for the track
#that is wasted for the MBR in DOS compatibility mode.  Sometimes a
#smaller track size that wastes fewer sectors will be slightly
#better, though the maximum savings is minimal (55 sectors).
#
#For a large device, you will probably want to interrupt this
#before it runs to completion.  Evaluating geometries with millions
#of tiny cylinders can take hours, and those are not likely to be
#considered desirable.
#
#Released to the public domain 15 June 2009 by Robert Nichols
#   AT comcast.net I am rnicholsNOSPAM
#   (Yes, NOSPAM really is part of my email address.)
########

restrk=0
if [ "$1" = -d ]; then
    restrk=1
    echo "Loss due to DOS compatibility mode considered"
    shift
fi
if [ -z "$1" -o "$1" = "-h" -o "$1" = "--help" ]; then
    echo "Usage: ${0##*/} [-d] total_sectors" >&2
    echo "  (Integer expression allowed for total_sectors)" >&2
    exit 1
fi
tsec=$(( ($1) + 0 ))	# Evaluate the input expression
maxspcyl=$((63*255))	# Max possible sectors per cylinder
mincyl=$(($tsec/$maxspcyl))
[ $mincyl -lt 1 ] && mincyl = 1
best_cap=0
cyl=$mincyl
full=
trap "echo \"Interrupted at cyl count = \$cyl\"; exit" 2
echo " H  * S  * C  for $tsec total sectors:"
while [ $cyl -le $(($tsec/8)) ]; do
    cylsize_p=$(($tsec/$cyl))
    minspt=$(($cylsize_p/255))
    [ $minspt -gt 63 ] && minspt=63
    [ $minspt -lt 1 ] && minspt=1
    spt=$minspt
    while [ $spt -le 63 ]; do
	hd=$(($cylsize_p/$spt))
	[ $hd -gt 255 ] && hd=255
	cap=$(($spt*$hd*$cyl))
	pcap=$(($spt*($hd*$cyl - $restrk)))
	if [ $pcap -ge $best_cap ]; then
	    best_cap=$pcap
	    [ $best_cap = $tsec ] && full=" 100%"
	    echo "$hd * $spt * $cyl = $pcap ($(($pcap*512)))$full"
	fi
	spt=$(($spt+1))
    done
    cyl=$((cyl+1))
done