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switch to fastrand (not actually any faster)

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This commit is contained in:
Joseph Montanaro 2021-07-19 11:45:51 -07:00
parent cade17a9a6
commit f2e0698608
2 changed files with 36 additions and 14 deletions
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4
combinators.nim
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@ -1,5 +1,5 @@
import algorithm, random, sugar
import fixedseq, game
import fastrand, fixedseq, game
proc nextPermutation(x: var FixedSeq): bool =
@ -93,4 +93,4 @@ proc randomFuture*(dice: FixedSeq, r: var Rand): FixedSeq[5, Die, int8] =
result.initFixedSeq
let order = dice.dup(shuffle(r))
for i, color in order:
result.add((color, r.rand(1..3)))
result.add((color, r.fastRand(1..3)))

42
fastrand.nim
View File

@ -17,13 +17,27 @@ proc formatRate(n: Natural, d: Duration): string =
result = formatNum(1_000_000'f64 * n.float64 / d.inMicroseconds.float64)
proc fastRand(r: var Rand, x: Natural): uint64 =
# return ((r.next shr 32) * x.uint64) shr 32
let x = x.uint64
if x <= (uint64.high shl 32):
return ((r.next shr 32) * x.uint64) shr 32
const upperBound = uint64(uint32.high)
proc fastRand*[T: Natural](r: var Rand, x: T): T =
# Nim ranges are usually inclusive, but this algorithm is exclusive
let x = x.uint64 + 1
let num = if x <= upperBound:
((r.next shr 32) * x.uint64) shr 32
else:
return r.next mod x.uint64
r.next mod x.uint64
result = T(num)
proc fastRand*(r: var Rand; x, y: Natural): Natural =
let lim = (y - x)
result = fastRand(r, lim) + x
proc fastRand*[T](r: var Rand, slice: HSlice[T, T]): T =
let n = fastRand(r, slice.a.Natural, slice.b.Natural)
result = T(n)
proc testFastRand(num = 1_000_000_000): Duration =
@ -44,9 +58,17 @@ proc testStdRand(num = 1_000_000_000): Duration =
# echo "std rand execution rate: ", 1000 * num / dur.inMilliseconds.int, " generated per second."
when isMainModule:
randomize()
var r = initRand(rand(int64))
let runs = 100_000_000
let fr = testFastRand(runs)
echo "fastrand execution rate: ", formatNum(1_000_000 * runs / fr.inMicroseconds.int)
let sr = testStdRand(runs)
echo "standard execution rate: ", formatNum(1_000_000 * runs / sr.inMicroseconds.int)
var totals: array[5..9, int]
for i in 1 .. runs:
let n = r.fastRand(5..9)
totals[n] += 1
echo totals
# let fr = testFastRand(runs)
# echo "fastrand execution rate: ", formatNum(1_000_000 * runs / fr.inMicroseconds.int)
# let sr = testStdRand(runs)
# echo "standard execution rate: ", formatNum(1_000_000 * runs / sr.inMicroseconds.int)