nim-dagger/codex/rng.nim

60 lines
1.5 KiB
Nim

## Nim-Codex
## 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/upraises
push: {.upraises: [].}
import pkg/libp2p/crypto/crypto
import pkg/bearssl/rand
type
RngSampleError = object of CatchableError
Rng* = ref HmacDrbgContext
var rng {.threadvar.}: Rng
proc instance*(t: type Rng): Rng =
if rng.isNil:
rng = newRng()
rng
# Random helpers: similar as in stdlib, but with HmacDrbgContext 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
while true:
let x = rng[].generate(uint64)
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 sample*[T](
rng: Rng, sample, exclude: openArray[T]): T
{.raises: [Defect, RngSampleError].} =
if sample == exclude:
raise newException(RngSampleError, "Sample and exclude arrays are the same!")
while true:
result = rng.sample(sample)
if exclude.find(result) != -1:
continue
break
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])