Remove unused RNG stuff from abstutil, and start to think about how to tease it apart a bit

Cargo.lock

@@ -30,8 +30,6 @@ dependencies = [
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 1.13.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "rand 0.7.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "rand_xorshift 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "scoped_threadpool 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.116 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.57 (registry+https://github.com/rust-lang/crates.io-index)",

abstutil/Cargo.toml

@@ -15,8 +15,6 @@ itertools = "0.9.0"
 lazy_static = "1.4.0"
 log = { version = "0.4.11", features=["std"] }
 num_cpus = "1.13.0"
-rand = "0.7.0"
-rand_xorshift = "0.2.0"
 scoped_threadpool = "0.1.9"
 serde = "1.0.116"
 serde_json = "1.0.57"

abstutil/src/lib.rs

@@ -1,7 +1,13 @@
+// The contents of this crate need to be organized better:
+//
+// - Timer (a mix of logging, profiling, and even parallel execution)
+// - IO utilities, some of which have web equivalents using include_dir
+// - A/B Street-specific filesystem paths
+// - true utility functions (collections, prettyprinting, CLI parsing
+
 mod cli;
 mod collections;
 mod io;
-mod random;
 mod time;
 
 pub use crate::cli::CmdArgs;
@@ -16,7 +22,6 @@ pub use crate::io::{
     serialize_btreemap, serialize_multimap, serialize_usize, serialized_size_bytes, slurp_file,
     to_json, write_binary, write_json, FileWithProgress,
 };
-pub use crate::random::{fork_rng, WeightedUsizeChoice};
 pub use crate::time::{
     elapsed_seconds, prettyprint_usize, start_profiler, stop_profiler, Parallelism, Profiler,
     Timer, TimerSink,

abstutil/src/random.rs

@@ -1,36 +0,0 @@
-use rand::distributions::{Distribution, WeightedIndex};
-use rand::{RngCore, SeedableRng};
-use rand_xorshift::XorShiftRng;
-use serde::{Deserialize, Serialize};
-
-// Need to explain this trick -- basically keeps consistency between two different simulations when
-// each one might make slightly different sequences of calls to the RNG.
-pub fn fork_rng(base_rng: &mut XorShiftRng) -> XorShiftRng {
-    XorShiftRng::from_seed([base_rng.next_u32() as u8; 16])
-}
-
-// Represents the probability of sampling 0, 1, 2, 3... The sum can be anything.
-// TODO Now unused
-#[derive(Clone, Debug, Serialize, Deserialize)]
-pub struct WeightedUsizeChoice {
-    pub weights: Vec<usize>,
-}
-
-impl WeightedUsizeChoice {
-    pub fn parse(string: &str) -> Option<WeightedUsizeChoice> {
-        let parts: Vec<&str> = string.split(',').collect();
-        if parts.is_empty() {
-            return None;
-        }
-        let mut weights: Vec<usize> = Vec::new();
-        for x in parts.into_iter() {
-            let x = x.parse::<usize>().ok()?;
-            weights.push(x);
-        }
-        Some(WeightedUsizeChoice { weights })
-    }
-
-    pub fn sample(&self, rng: &mut XorShiftRng) -> usize {
-        WeightedIndex::new(&self.weights).unwrap().sample(rng)
-    }
-}

sim/src/make/activity_model.rs

@@ -1,3 +1,4 @@
+use crate::make::fork_rng;
 use crate::{
     IndividTrip, PersonID, PersonSpec, Scenario, ScenarioGenerator, SpawnTrip, TripEndpoint,
     TripMode, TripPurpose,
@@ -153,7 +154,7 @@ impl ScenarioGenerator {
                     }
                 };
 
-                (home, work, abstutil::fork_rng(rng))
+                (home, work, fork_rng(rng))
             })
             .collect();
 

sim/src/make/mod.rs

@@ -16,3 +16,11 @@ pub use self::scenario::{
     IndividTrip, OffMapLocation, PersonSpec, Scenario, SpawnTrip, TripPurpose,
 };
 pub use self::spawner::{TripSpawner, TripSpec};
+use rand::{RngCore, SeedableRng};
+use rand_xorshift::XorShiftRng;
+
+// Need to explain this trick -- basically keeps consistency between two different simulations when
+// each one might make slightly different sequences of calls to the RNG.
+pub fn fork_rng(base_rng: &mut XorShiftRng) -> XorShiftRng {
+    XorShiftRng::from_seed([base_rng.next_u32() as u8; 16])
+}

sim/src/make/scenario.rs

@@ -1,3 +1,4 @@
+use crate::make::fork_rng;
 use crate::{
     CarID, DrivingGoal, OrigPersonID, ParkingSpot, PersonID, SidewalkPOI, SidewalkSpot, Sim,
     TripEndpoint, TripMode, TripSpec, Vehicle, VehicleSpec, VehicleType, BIKE_LENGTH,
@@ -181,7 +182,7 @@ impl Scenario {
             for (t, maybe_idx) in p.trips.iter().zip(vehicle_foreach_trip) {
                 // The RNG call might change over edits for picking the spawning lane from a border
                 // with multiple choices for a vehicle type.
-                let mut tmp_rng = abstutil::fork_rng(rng);
+                let mut tmp_rng = fork_rng(rng);
                 let spec = t.trip.clone().to_trip_spec(
                     maybe_idx.map(|idx| person.vehicles[idx].id),
                     &mut tmp_rng,
@@ -351,7 +352,7 @@ fn seed_parked_cars(
     }
     // Changing parking on one road shouldn't affect far-off roads. Fork carefully.
     for r in map.all_roads() {
-        let mut tmp_rng = abstutil::fork_rng(base_rng);
+        let mut tmp_rng = fork_rng(base_rng);
         if let Some(ref mut spots) = open_spots_per_road.get_mut(&r.id) {
             spots.shuffle(&mut tmp_rng);
         }