nim-codex/dagger/rng.nim

43 lines
1.1 KiB
Nim

## Nim-Dagger
## Copyright (c) 2021 Status Research & Development GmbH
## Licensed under either of
## * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
## * MIT license ([LICENSE-MIT](LICENSE-MIT))
## at your option.
## This file may not be copied, modified, or distributed except according to
## those terms.
import pkg/libp2p/crypto/crypto
import pkg/bearssl
type
Rng* = ref BrHmacDrbgContext
var rng {.threadvar.}: Rng
proc instance*(t: type Rng): Rng =
if rng.isNil:
rng = newRng()
rng
# Random helpers: similar as in stdlib, but with BrHmacDrbgContext rng
# TODO: Move these somewhere else?
const randMax = 18_446_744_073_709_551_615'u64
proc rand*(rng: Rng, max: Natural): int =
if max == 0: return 0
var x: uint64
while true:
brHmacDrbgGenerate(addr rng[], addr x, csize_t(sizeof(x)))
if x < randMax - (randMax mod (uint64(max) + 1'u64)): # against modulo bias
return int(x mod (uint64(max) + 1'u64))
proc sample*[T](rng: Rng, a: openArray[T]): T =
result = a[rng.rand(a.high)]
proc shuffle*[T](rng: Rng, a: var openArray[T]) =
for i in countdown(a.high, 1):
let j = rng.rand(i)
swap(a[i], a[j])