gno.land/r/moul/x/daily/bitsetdemo/v0⧉

1// Package bitsetdemo is a small gnoweb demo of the dense bit vector provided by2// the [p/moul/x/daily/bitset](/p/moul/x/daily/bitset/v0) library: it sieves the3// primes under 100 into a bit set and shows the set algebra on two small sets.4//5// It contains no bit-twiddling of its own — storage, popcount and the set6// operations all come from the library. Stateless, so Render is deterministic.7package bitsetdemo89import (10	"strconv"11	"strings"1213	"gno.land/p/moul/x/daily/bitset/v0"14)1516// limit bounds the sieve shown on the page.17const limit = 1001819// primes returns a bit set of the primes below limit, sieved with the bit set20// itself as the composite marker.21func primes() *bitset.BitSet {22	composite := bitset.New(limit)23	out := bitset.New(limit)24	for p := 2; p < limit; p++ {25		if composite.Has(p) {26			continue27		}28		out.Set(p)29		for m := p * p; m < limit; m += p {30			composite.Set(m)31		}32	}33	return out34}3536// Render renders the demo for gnoweb.37func Render(path string) string {38	var b strings.Builder39	b.WriteString("# BitSet\n\n")40	b.WriteString("A dense bit vector, demoing the ")41	b.WriteString("[`p/moul/x/daily/bitset`](/p/moul/x/daily/bitset/v0) library.\n\n")4243	p := primes()44	b.WriteString("## Primes under ")45	b.WriteString(strconv.Itoa(limit))46	b.WriteString("\n\n**")47	b.WriteString(strconv.Itoa(p.Count()))48	b.WriteString("** set bits in ")49	b.WriteString(strconv.Itoa(p.Cap()))50	b.WriteString(" bits of capacity:\n\n")51	b.WriteString(list(p.Slice()))5253	small := bitset.FromSlice(16, []int{1, 2, 3, 5, 8})54	even := bitset.FromSlice(16, []int{2, 4, 6, 8, 10})55	b.WriteString("\n## Set algebra\n\n")56	b.WriteString("| set | bits |\n|---|---|\n")57	row(&b, "a", small)58	row(&b, "b", even)59	row(&b, "a ∪ b", bitset.Union(small, even))60	row(&b, "a ∩ b", bitset.Intersect(small, even))61	row(&b, "a \\ b", bitset.Difference(small, even))62	row(&b, "a △ b", bitset.SymmetricDifference(small, even))63	return b.String()64}6566func row(b *strings.Builder, name string, s *bitset.BitSet) {67	b.WriteString("| ")68	b.WriteString(name)69	b.WriteString(" | `")70	b.WriteString(list1(s.Slice()))71	b.WriteString("` |\n")72}7374func list(xs []int) string {75	if len(xs) == 0 {76		return "_none_\n"77	}78	return "`" + list1(xs) + "`\n"79}8081func list1(xs []int) string {82	parts := []string{}83	for _, x := range xs {84		parts = append(parts, strconv.Itoa(x))85	}86	return strings.Join(parts, " ")87}88