v0.2.0

ADDED:
* num-nets subcommand' this is MUCH much faster than actually splitting
  if you're trying to figure out how many times a given subnet fits into
  a network.

netsplit/conts.go

@@ -8,6 +8,12 @@ import (
 	`github.com/go-resty/resty/v2`
 )
 
+const (
+	maxBitsv4 uint8 = 32
+	maxBitsv6 uint8 = 128
+	maxBits   uint8 = maxBitsv6
+)
+
 const (
 	cachedirEnvName string = "SBNTR_RSVCACHE_DIR"
 	// https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml

netsplit/funcs.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"encoding/xml"
 	"fmt"
+	`math`
 	"net"
 	"net/netip"
 	"strings"
@@ -375,6 +376,38 @@ func MaskInvert(mask net.IPMask) (inverted net.IPMask) {
 	return
 }
 
+/*
+	NumNets returns the number of times prefix size subnet fits into prefix size network.
+
+	It will error if network is larger than 128 or if subnet is smaller than network.
+
+	This is MUCH more performant than splitting out an actual network into explicit subnets,
+	and does not require an actual network.
+*/
+func NumNets(subnet, network uint8) (numNets uint, ipv6Only bool, err error) {
+
+	var x float64
+
+	// network cannot be higher than 128, as that's the maximum for IPv6.
+	if network > maxBits {
+		err = ErrBadPrefixLen
+		return
+	}
+	if subnet < network {
+		err = ErrBigPrefix
+		return
+	}
+	if network > maxBitsv4 {
+		ipv6Only = true
+	}
+
+	x = float64(subnet - network)
+
+	numNets = uint(math.Pow(2, x))
+
+	return
+}
+
 // Parse parses b for JSON/XML/YAML and tries to return a StructuredResults from it.
 func Parse(b []byte) (s *StructuredResults, err error) {