gno.land/r/moul/x/daily/sievedemo/v0⧉

1// Package sievedemo is a small gnoweb demo of the Sieve of Eratosthenes2// provided by the [p/moul/x/daily/sieve](/p/moul/x/daily/sieve/v0) library: it3// renders the primes up to MaxN, the first 100 primes, and an interactive4// "primes up to n" grid.5//6// It contains no sieve logic of its own — everything comes from7// `sieve.PrimesUpTo` and `sieve.MaxN`.8package sievedemo910import (11	"strconv"12	"strings"1314	"gno.land/p/moul/x/daily/sieve/v0"15)1617// Render renders the sieve for gnoweb.18//19//	Render("")      / Render("/") -> first 100 primes + total count up to MaxN20//	Render("/<n>")               -> every prime <= n, laid out as a grid21func Render(path string) string {22	n, hasN := parseN(path)2324	var b strings.Builder25	b.WriteString("# Sieve of Eratosthenes\n\n")26	b.WriteString("A deterministic on-chain port of Go's classic concurrent prime-sieve example, ")27	b.WriteString("demoing the [`p/moul/x/daily/sieve`](/p/moul/x/daily/sieve/v0) library.\n\n")2829	if !hasN {30		primes := sieve.PrimesUpTo(sieve.MaxN)31		b.WriteString("There are **")32		b.WriteString(strconv.Itoa(len(primes)))33		b.WriteString("** primes up to ")34		b.WriteString(strconv.Itoa(sieve.MaxN))35		b.WriteString(".\n\n")36		b.WriteString("## First 100 primes\n\n")37		first := primes38		if len(first) > 100 {39			first = first[:100]40		}41		b.WriteString(grid(first, 10))42		b.WriteString("\n> Try `/500` or `/1000` to sieve up to any n (max ")43		b.WriteString(strconv.Itoa(sieve.MaxN))44		b.WriteString(").\n")45		return b.String()46	}4748	if n < 2 {49		b.WriteString("No primes <= ")50		b.WriteString(strconv.Itoa(n))51		b.WriteString(".\n")52		return b.String()53	}5455	clamped := n56	if clamped > sieve.MaxN {57		clamped = sieve.MaxN58	}59	primes := sieve.PrimesUpTo(clamped)60	b.WriteString("## Primes up to ")61	b.WriteString(strconv.Itoa(clamped))62	if clamped != n {63		b.WriteString(" (clamped from ")64		b.WriteString(strconv.Itoa(n))65		b.WriteString(")")66	}67	b.WriteString("\n\n")68	b.WriteString("Count: **")69	b.WriteString(strconv.Itoa(len(primes)))70	b.WriteString("**\n\n")71	b.WriteString(grid(primes, 10))72	return b.String()73}7475// parseN extracts n from a Render path like "/1000". Returns hasN=false for76// the empty/root path.77func parseN(path string) (int, bool) {78	s := strings.TrimSpace(path)79	s = strings.TrimPrefix(s, "/")80	if s == "" {81		return 0, false82	}83	// keep only the first segment84	if i := strings.IndexByte(s, '/'); i >= 0 {85		s = s[:i]86	}87	v, err := strconv.Atoi(s)88	if err != nil {89		return 0, false90	}91	return v, true92}9394// grid formats primes into a Markdown table with `cols` columns per row.95func grid(primes []int, cols int) string {96	if len(primes) == 0 {97		return "_none_\n"98	}99	if cols < 1 {100		cols = 1101	}102103	var b strings.Builder104	// header + separator so gnoweb renders it as a table105	b.WriteString("|")106	for c := 0; c < cols; c++ {107		b.WriteString(" · |")108	}109	b.WriteString("\n|")110	for c := 0; c < cols; c++ {111		b.WriteString("---|")112	}113	b.WriteString("\n")114115	for i := 0; i < len(primes); i += cols {116		b.WriteString("|")117		for c := 0; c < cols; c++ {118			b.WriteString(" ")119			if i+c < len(primes) {120				b.WriteString(strconv.Itoa(primes[i+c]))121			}122			b.WriteString(" |")123		}124		b.WriteString("\n")125	}126	return b.String()127}128