IMO, this is conceptually simpler and generates nice ranges: 
#! perl -slw
use strict;

our $N //= 2;
our $M //= 1e6;

my $size = $M + 1;
my $step0 = int ($size / $N);
my $big_ranges = $size % $N;
my $start = 0;
my @ranges;
for (1..$N) {
    my $step = $step0 + ($_ <= $big_ranges ? 1 : 0);
    push @ranges, [$start, $start + $step - 1];
    $start += $step;
}

printf "%2d : from %7d to %7d (%7d)\n",
    $_, @{ $ranges[ $_ ] },
    $ranges[ $_ ][ 1 ] - $ranges[ $_ ][ 0 ] + 1
    for 0 .. $#ranges;

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In reply to Re: Split range 0 to M into N non-overlapping (roughly equal) ranges. by salva
in thread Split range 0 to M into N non-overlapping (roughly equal) ranges. by BrowserUk

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