v0.2.5

ADDED:
* num-addrs subcommand, to get the number of hosts/addresses in a given
  prefix length
* get-net subcommand, to more easily get a single subnet from either the
  beginning or the end of a prefix. (MUCH FASTER than CIDR-splitting!)

netsplit/funcs_prefixgetter.go

@@ -0,0 +1,102 @@
+package netsplit
+
+import (
+	`fmt`
+	`net/netip`
+
+	`go4.org/netipx`
+)
+
+// Split is to conform to a NetSplitter, though a PrefixGetter is *technically* not a splitter.
+func (p *PrefixGetter) Split() (nets []*netip.Prefix, remaining *netipx.IPSet, err error) {
+
+	var ok bool
+	var base netip.Prefix
+	var vlsmS *VLSMSplitter
+	var addr netip.Addr
+	var maxPfxLen uint8 = maxBitsv4
+	var ipsb *netipx.IPSetBuilder = new(netipx.IPSetBuilder)
+
+	if p == nil || p.PrefixLength == 0 || p.BaseSplitter == nil || p.network == nil {
+		return
+	}
+
+	if err = validate.Struct(p); err != nil {
+		return
+	}
+
+	// If the position is "first", we can simply call a VLSM.
+	if p.Pos == "first" {
+		vlsmS = &VLSMSplitter{
+			Ascending:     false,
+			Explicit:      false,
+			PrefixLengths: []uint8{p.PrefixLength},
+			BaseSplitter:  p.BaseSplitter,
+		}
+		if nets, remaining, err = vlsmS.Split(); err != nil {
+			return
+		}
+		return
+	}
+
+	if p.Pos != "last" {
+		err = ErrUnknownPos
+		return
+	}
+
+	// Otherwise this gets... messy.
+	if base, ok = netipx.FromStdIPNet(p.network); !ok {
+		err = ErrBadBoundary
+		return
+	}
+	if !base.IsValid() {
+		err = ErrBadBoundary
+		return
+	}
+	ipsb = new(netipx.IPSetBuilder)
+	ipsb.AddPrefix(base.Masked())
+
+	// First if it's a single host prefix, ezpz gg no re.
+	if base.Addr().Is6() {
+		maxPfxLen = maxBitsv6
+	}
+	if p.PrefixLength == maxPfxLen {
+		nets = make([]*netip.Prefix, 1)
+		nets[0] = new(netip.Prefix)
+		addr = netipx.PrefixLastIP(base)
+		fmt.Println(addr.String())
+		if *nets[0], err = addr.Prefix(int(p.PrefixLength)); err != nil {
+			return
+		}
+		ipsb.Remove(addr)
+		if remaining, err = ipsb.IPSet(); err != nil {
+			return
+		}
+		return
+	}
+
+	// Otherwise this gets... interesting.
+	/*
+		For IPv4, performance NORMALLY would be "fine" on modern hardware with:
+			1. straight CIDR-splitting
+			2. grabbing the last prefix
+			3. condensing the leading prefixes to a new IPSet
+		But even this can take a long time (see CIDRSplitter.Split comments).
+
+		In almost all cases (unless subnetting like, n+12 prefix length),
+		IPv6 takes WAY too long.
+
+		So use the same function (LastSubnetPfx) for both cases.
+	*/
+	nets = make([]*netip.Prefix, 1)
+	nets[0] = new(netip.Prefix)
+	if *nets[0], err = LastSubnetPfx(base, p.PrefixLength); err != nil {
+		return
+	}
+	ipsb.RemovePrefix(*nets[0])
+	if remaining, err = ipsb.IPSet(); err != nil {
+		return
+	}
+
+	return
+}