1.75 -> 1-3/4

[Emanuel Berg <moasen@zoho.com>]

Did anyone do the equivalent of this ("ths" zsh
below) in Elisp or any other Lisp? Just asking
before I do it myself. The algorithm should be
straightforward, but it uses recursion which
I plan to replace by a loop in the Elisp
version. But it looks good otherwise, right?

Before anyone tries to use it on a bicycle
tire, note that "[a] 26x1.5 tire and a 26x1-1/2
tire are different tire sizing systems" (JL on
rec.bicycles.tech). Read more here [1]

ths () {
    local value=$1
    local denom=${2:-16}
    local whole=$(( int(floor($value)) ))
    local rest=$(( $value - $whole ))
    local frac=$(( int(rint($rest * $denom)) ))
    if (( $frac > 0 && $(( $frac % 2 )) == 0 )); then
        local new_denom=$(( denom / 2 ))
        ths $value $new_denom
    else
        local frace
        (( $frac > 0 )) && frace=-${frac}/${denom}
        echo ${whole}${frace}
    fi
}
# $ ths 2.0
# 2
# $ ths 1.75
# 1-3/4

[1] http://www.sheldonbrown.com/tire-sizing.html

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