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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)
}
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