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Rework random(6)

Fix putchar(3) handling and a number of other issues in the random(6)
code. In -e mode, avoid bias due to truncation of the return code to
8 bits. In default mode, actually treat the denominator as a floating
point number and print the line with a probability of 1 / denominator.
This allows e.g. printing 2/3 of stdin with 'random 1.5'.

Includes code for uniform random floats by Taylor R. Campbell from
https://mumble.net/~campbell/2014/04/28/uniform-random-float
and clz64() by me.

From lucic71 () bronze ! ctrl-c ! club, thanks.

ok deraadt

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.\"     @(#)random.6	8.2 (Berkeley) 3/31/94
.\"
.Dd $Mdocdate: August 23 2022 $
.Dt RANDOM 6
.Os
.Sh NAME
.Nm random
.Nd random lines from a file or random numbers
.Sh SYNOPSIS
.Nm random
.Op Fl er
.Op Ar denominator
.Sh DESCRIPTION
.Nm
reads lines from the standard input and copies them to the standard
output with a probability of 1/denominator.
The
.Ar denominator
must be at least 1,
its default value is 2.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl e
If the
.Fl e
option is specified,
.Nm
does not read or write anything, and simply exits with a random
exit value of 0 to the minimum of 255 and
.Ar denominator
\&- 1, inclusive.
.It Fl r
The
.Fl r
option guarantees that the output is unbuffered.
.El
.Sh SEE ALSO
.Xr fortune 6