From 4247abe6014593bdda0a4a8035c60cffeb19d993 Mon Sep 17 00:00:00 2001
From: Josh Stone <cuviper@gmail.com>
Date: Fri, 5 Mar 2021 09:46:19 -0800
Subject: [PATCH] implement xorshift* for benchmarking

---
 Cargo.toml                 |  3 ---
 benches/bigint.rs          |  7 ++-----
 benches/gcd.rs             |  7 ++-----
 benches/rng/mod.rs         | 38 ++++++++++++++++++++++++++++++++++++++
 benches/roots.rs           |  9 +++------
 ci/big_rand/src/torture.rs |  2 +-
 6 files changed, 46 insertions(+), 20 deletions(-)
 create mode 100644 benches/rng/mod.rs

diff --git a/Cargo.toml b/Cargo.toml
index c6aadb7a..6e54ee32 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -72,6 +72,3 @@ default-features = false
 
 [build-dependencies]
 autocfg = "1"
-
-[dev-dependencies]
-rand_xorshift = "0.3"
diff --git a/benches/bigint.rs b/benches/bigint.rs
index 8163aa64..b7f5fd21 100644
--- a/benches/bigint.rs
+++ b/benches/bigint.rs
@@ -5,14 +5,11 @@ extern crate test;
 
 use num_bigint::{BigInt, BigUint, RandBigInt};
 use num_traits::{FromPrimitive, Num, One, Zero};
-use rand::prelude::*;
-use rand_xorshift::XorShiftRng;
 use std::mem::replace;
 use test::Bencher;
 
-fn get_rng() -> impl Rng {
-    XorShiftRng::seed_from_u64(0x1234_5678_9abc_def0)
-}
+mod rng;
+use rng::get_rng;
 
 fn multiply_bench(b: &mut Bencher, xbits: u64, ybits: u64) {
     let mut rng = get_rng();
diff --git a/benches/gcd.rs b/benches/gcd.rs
index 61028a7d..c211b6ef 100644
--- a/benches/gcd.rs
+++ b/benches/gcd.rs
@@ -6,13 +6,10 @@ extern crate test;
 use num_bigint::{BigUint, RandBigInt};
 use num_integer::Integer;
 use num_traits::Zero;
-use rand::prelude::*;
-use rand_xorshift::XorShiftRng;
 use test::Bencher;
 
-fn get_rng() -> impl Rng {
-    XorShiftRng::seed_from_u64(0x1234_5678_9abc_def0)
-}
+mod rng;
+use rng::get_rng;
 
 fn bench(b: &mut Bencher, bits: u64, gcd: fn(&BigUint, &BigUint) -> BigUint) {
     let mut rng = get_rng();
diff --git a/benches/rng/mod.rs b/benches/rng/mod.rs
new file mode 100644
index 00000000..33e4f0fa
--- /dev/null
+++ b/benches/rng/mod.rs
@@ -0,0 +1,38 @@
+use rand::RngCore;
+
+pub(crate) fn get_rng() -> impl RngCore {
+    XorShiftStar {
+        a: 0x0123_4567_89AB_CDEF,
+    }
+}
+
+/// Simple `Rng` for benchmarking without additional dependencies
+struct XorShiftStar {
+    a: u64,
+}
+
+impl RngCore for XorShiftStar {
+    fn next_u32(&mut self) -> u32 {
+        self.next_u64() as u32
+    }
+
+    fn next_u64(&mut self) -> u64 {
+        // https://en.wikipedia.org/wiki/Xorshift#xorshift*
+        self.a ^= self.a >> 12;
+        self.a ^= self.a << 25;
+        self.a ^= self.a >> 27;
+        self.a.wrapping_mul(0x2545_F491_4F6C_DD1D)
+    }
+
+    fn fill_bytes(&mut self, dest: &mut [u8]) {
+        for chunk in dest.chunks_mut(8) {
+            let bytes = self.next_u64().to_le_bytes();
+            let slice = &bytes[..chunk.len()];
+            chunk.copy_from_slice(slice)
+        }
+    }
+
+    fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), rand::Error> {
+        Ok(self.fill_bytes(dest))
+    }
+}
diff --git a/benches/roots.rs b/benches/roots.rs
index 0f365ada..7afc4f76 100644
--- a/benches/roots.rs
+++ b/benches/roots.rs
@@ -4,10 +4,11 @@
 extern crate test;
 
 use num_bigint::{BigUint, RandBigInt};
-use rand::prelude::*;
-use rand_xorshift::XorShiftRng;
 use test::Bencher;
 
+mod rng;
+use rng::get_rng;
+
 // The `big64` cases demonstrate the speed of cases where the value
 // can be converted to a `u64` primitive for faster calculation.
 //
@@ -16,10 +17,6 @@ use test::Bencher;
 //
 // The `big2k` and `big4k` cases are too big for `f64`, and use a simpler guess.
 
-fn get_rng() -> impl Rng {
-    XorShiftRng::seed_from_u64(0x1234_5678_9abc_def0)
-}
-
 fn check(x: &BigUint, n: u32) {
     let root = x.nth_root(n);
     if n == 2 {
diff --git a/ci/big_rand/src/torture.rs b/ci/big_rand/src/torture.rs
index 58400883..72059ef2 100644
--- a/ci/big_rand/src/torture.rs
+++ b/ci/big_rand/src/torture.rs
@@ -3,7 +3,7 @@ use num_traits::Zero;
 use rand::prelude::*;
 use rand_xorshift::XorShiftRng;
 
-fn get_rng() -> impl Rng {
+fn get_rng() -> XorShiftRng {
     XorShiftRng::seed_from_u64(0x1234_5678_9abc_def0)
 }