js: initial work on porting rand module to JS backend (#11188)

vlib/rand/rand.c.v

@@ -0,0 +1,127 @@
+module rand
+
+import time
+// uuid_v4 generates a random (v4) UUID
+// See https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_(random)
+
+pub fn uuid_v4() string {
+	buflen := 36
+	mut buf := unsafe { malloc_noscan(37) }
+	mut i_buf := 0
+	mut x := u64(0)
+	mut d := byte(0)
+	for i_buf < buflen {
+		mut c := 0
+		x = default_rng.u64()
+		// do most of the bit manipulation at once:
+		x &= 0x0F0F0F0F0F0F0F0F
+		x += 0x3030303030303030
+		// write the ASCII codes to the buffer:
+		for c < 8 && i_buf < buflen {
+			d = byte(x)
+			unsafe {
+				buf[i_buf] = if d > 0x39 { d + 0x27 } else { d }
+			}
+			i_buf++
+			c++
+			x = x >> 8
+		}
+	}
+	// there are still some random bits in x:
+	x = x >> 8
+	d = byte(x)
+	unsafe {
+		buf[19] = if d > 0x39 { d + 0x27 } else { d }
+		buf[8] = `-`
+		buf[13] = `-`
+		buf[18] = `-`
+		buf[23] = `-`
+		buf[14] = `4`
+		buf[buflen] = 0
+		return buf.vstring_with_len(buflen)
+	}
+}
+
+const (
+	ulid_encoding = '0123456789ABCDEFGHJKMNPQRSTVWXYZ'
+)
+
+// ulid generates an Unique Lexicographically sortable IDentifier.
+// See https://github.com/ulid/spec .
+// NB: ULIDs can leak timing information, if you make them public, because
+// you can infer the rate at which some resource is being created, like
+// users or business transactions.
+// (https://news.ycombinator.com/item?id=14526173)
+pub fn ulid() string {
+	return ulid_at_millisecond(u64(time.utc().unix_time_milli()))
+}
+
+// ulid_at_millisecond does the same as `ulid` but takes a custom Unix millisecond timestamp via `unix_time_milli`.
+pub fn ulid_at_millisecond(unix_time_milli u64) string {
+	buflen := 26
+	mut buf := unsafe { malloc_noscan(27) }
+	mut t := unix_time_milli
+	mut i := 9
+	for i >= 0 {
+		unsafe {
+			buf[i] = rand.ulid_encoding[t & 0x1F]
+		}
+		t = t >> 5
+		i--
+	}
+	// first rand set
+	mut x := default_rng.u64()
+	i = 10
+	for i < 19 {
+		unsafe {
+			buf[i] = rand.ulid_encoding[x & 0x1F]
+		}
+		x = x >> 5
+		i++
+	}
+	// second rand set
+	x = default_rng.u64()
+	for i < 26 {
+		unsafe {
+			buf[i] = rand.ulid_encoding[x & 0x1F]
+		}
+		x = x >> 5
+		i++
+	}
+	unsafe {
+		buf[26] = 0
+		return buf.vstring_with_len(buflen)
+	}
+}
+
+// string_from_set returns a string of length `len` containing random characters sampled from the given `charset`
+pub fn string_from_set(charset string, len int) string {
+	if len == 0 {
+		return ''
+	}
+	mut buf := unsafe { malloc_noscan(len + 1) }
+	for i in 0 .. len {
+		unsafe {
+			buf[i] = charset[intn(charset.len)]
+		}
+	}
+	unsafe {
+		buf[len] = 0
+	}
+	return unsafe { buf.vstring_with_len(len) }
+}
+
+// string returns a string of length `len` containing random characters in range `[a-zA-Z]`.
+pub fn string(len int) string {
+	return string_from_set(english_letters, len)
+}
+
+// hex returns a hexadecimal number of length `len` containing random characters in range `[a-f0-9]`.
+pub fn hex(len int) string {
+	return string_from_set(hex_chars, len)
+}
+
+// ascii returns a random string of the printable ASCII characters with length `len`.
+pub fn ascii(len int) string {
+	return string_from_set(ascii_chars, len)
+}