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<algorithm>: Optimize sample() and shuffle() with Lemire's algorithm #5735

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Merged
merged 12 commits into from
Sep 25, 2025
Merged

<algorithm>: Optimize sample() and shuffle() with Lemire's algorithm #5735

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bcadc2a
Add benchmarks for sample() and shuffle().
StephanTLavavej Sep 22, 2025
8c0cbe6
Move `_Rng_from_urng_v2` up to `<algorithm>`, no other changes.
StephanTLavavej Sep 21, 2025
5fa2951
Move `_Has_static_min_max` up to `<algorithm>`, no other changes.
StephanTLavavej Sep 22, 2025
30f3317
Extract `_Rng_from_urng_v1_or_v2`.
StephanTLavavej Sep 22, 2025
e62b977
Cleanup `_Rng_from_urng_v2`: `static constexpr` => `constexpr` for a …
StephanTLavavej Sep 22, 2025
ae1fa8a
Fix URBG usage: `min()` and `max()` must be `constexpr`.
StephanTLavavej Sep 21, 2025
1829230
Fix URBG usage: Must provide `result_type`, must be unsigned integer.
StephanTLavavej Sep 23, 2025
ca969a9
Behavioral change: Use `_Rng_from_urng_v1_or_v2` to optimize `sample(…
StephanTLavavej Sep 22, 2025
f0c8420
Fix warning C4018: '<': signed/unsigned mismatch
StephanTLavavej Sep 23, 2025
bb03a9e
Fix warning C4365: 'initializing': conversion from 'int' to 'unsigned…
StephanTLavavej Sep 23, 2025
fedbd6c
Fix error C2397: conversion from 'const int' to 'unsigned __int64' re…
StephanTLavavej Sep 23, 2025
01090a7
Fix warning C4018: '<': signed/unsigned mismatch
StephanTLavavej Sep 23, 2025
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14 changes: 8 additions & 6 deletions tests/std/tests/P0896R4_ranges_alg_shuffle/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
#include <algorithm>
#include <cassert>
#include <concepts>
#include <cstdint>
#include <cstdio>
#include <random>
#include <ranges>
Expand Down Expand Up @@ -53,14 +54,15 @@ struct instantiator {

void test_urbg() { // COMPILE-ONLY
struct RandGen {
static constexpr bool min() {
return false;
using result_type = uint16_t; // N5014 [rand.req.urng]/3
static constexpr result_type min() {
return 3;
}
static constexpr bool max() {
return true;
static constexpr result_type max() {
return 1729;
}
bool operator()() & {
return false;
result_type operator()() & {
return 4;
Comment on lines +57 to +65
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@davidmrdavid davidmrdavid Sep 25, 2025

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just to be triple sure - these numbers are completely arbitrary, right? I'd be a fan of calling that out, but I won't insist.

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@StephanTLavavej StephanTLavavej Sep 25, 2025

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Yes, it's a compile-time only test, and the actual values involved are not relevant.

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@StephanTLavavej StephanTLavavej Sep 25, 2025

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I've made a note to add comments to this generator in a followup PR.

}
};

Expand Down