23 lines
708 B
Nim
23 lines
708 B
Nim
import bearssl/rand
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## Random helpers: similar as in stdlib, but with HmacDrbgContext rng
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# TODO: Move these somewhere else?
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const randMax = 18_446_744_073_709_551_615'u64
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proc rand*(rng: var HmacDrbgContext, max: Natural): int =
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if max == 0: return 0
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var x: uint64
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while true:
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hmacDrbgGenerate(rng, addr x, csize_t(sizeof(x)))
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if x < randMax - (randMax mod (uint64(max) + 1'u64)): # against modulo bias
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return int(x mod (uint64(max) + 1'u64))
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proc sample*[T](rng: var HmacDrbgContext, a: openArray[T]): T =
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result = a[rng.rand(a.high)]
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proc shuffle*[T](rng: var HmacDrbgContext, a: var openArray[T]) =
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for i in countdown(a.high, 1):
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let j = rng.rand(i)
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swap(a[i], a[j])
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