From f96b2b2113fac3c1d283afa65cbca42750e000df Mon Sep 17 00:00:00 2001
From: Joe Richey <joerichey@google.com>
Date: Sun, 6 Sep 2020 22:44:08 -0700
Subject: [PATCH] benches: Add benchmarks

This allows comparison of alternative implementaitons, and to the
f64::sqrt() implementation.

Signed-off-by: Joe Richey <joerichey@google.com>
---
 benches/sqrt.rs | 73 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 benches/sqrt.rs

diff --git a/benches/sqrt.rs b/benches/sqrt.rs
new file mode 100644
index 0000000..693fc1c
--- /dev/null
+++ b/benches/sqrt.rs
@@ -0,0 +1,73 @@
+#![feature(test)]
+
+extern crate test;
+use test::{black_box, Bencher};
+
+extern crate integer_sqrt;
+use integer_sqrt::IntegerSquareRoot;
+
+// Use f64::sqrt to compute the integer sqrt
+fn isqrt_via_f64(n: u64) -> u64 {
+    let cand = (n as f64).sqrt() as u64;
+    // Rounding can cause off-by-one errors
+    if let Some(prod) = cand.checked_mul(cand) {
+        if prod <= n {
+            return cand;
+        }
+    }
+    cand - 1
+}
+
+#[bench]
+fn isqrt_small(b: &mut Bencher) {
+    let small = 63u64;
+    b.iter(|| {
+        let n = black_box(small);
+        assert_eq!(n.integer_sqrt_checked(), Some(7));
+    })
+}
+
+#[bench]
+fn isqrt_med(b: &mut Bencher) {
+    let med = 10_000_000_000u64; // 10^10
+    b.iter(|| {
+        let n = black_box(med);
+        assert_eq!(n.integer_sqrt_checked(), Some(100_000)); // 10^5
+    })
+}
+
+#[bench]
+fn isqrt_large(b: &mut Bencher) {
+    let large = u64::MAX;
+    b.iter(|| {
+        let n = black_box(large);
+        assert_eq!(n.integer_sqrt_checked(), Some((1u64 << 32) - 1));
+    })
+}
+
+#[bench]
+fn isqrt_f64_small(b: &mut Bencher) {
+    let small = 63u64;
+    b.iter(|| {
+        let n = black_box(small);
+        assert_eq!(isqrt_via_f64(n), 7);
+    })
+}
+
+#[bench]
+fn isqrt_f64_med(b: &mut Bencher) {
+    let med = 10_000_000_000u64; // 10^10
+    b.iter(|| {
+        let n = black_box(med);
+        assert_eq!(isqrt_via_f64(n), 100_000); // 10^5
+    })
+}
+
+#[bench]
+fn isqrt_f64_large(b: &mut Bencher) {
+    let large = u64::MAX;
+    b.iter(|| {
+        let n = black_box(large);
+        assert_eq!(isqrt_via_f64(n), (1u64 << 32) - 1);
+    })
+}