Add crc32fast

experimental/hashcmp/Cargo.toml

@@ -27,5 +27,6 @@ t1ha = "0.1.0"
 wyhash = "0.5.0"
 twox-hash = "1.6.3"
 xxhash-rust = { version = "0.8.7", features = ["xxh64", "xxh32", "xxh3"] }
+crc32fast = "1.3"
 
 [dev-dependencies]

experimental/hashcmp/src/bin/crc32fast.rs

@@ -0,0 +1,55 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+#![no_main] // https://github.com/unicode-org/icu4x/issues/395
+
+use std::hash::Hasher;
+use std::collections::BTreeSet;
+
+const ALPHANUMS: &[u8] = b"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_";
+
+#[no_mangle]
+fn main(_argc: isize, _argv: *const *const u8) -> isize {
+    let seed = std::hint::black_box(2023u32);
+    let mut hashes = BTreeSet::new();
+    let mut hashes_32bit = BTreeSet::new();
+    let mut record = |hashed| {
+        hashes.insert(hashed);
+        hashes_32bit.insert(hashed as u32);
+    };
+    let mut cases = 0;
+    for i in 0u8..255 {
+        let mut hasher = crc32fast::Hasher::new_with_initial(seed);
+        hasher.write_u8(i);
+        record(hasher.finish());
+        cases += 1;
+    }
+    for a in ALPHANUMS.iter() {
+        for b in ALPHANUMS.iter() {
+            for c in ALPHANUMS.iter() {
+                let mut hasher = crc32fast::Hasher::new_with_initial(seed);
+                hasher.write_u8(*a);
+                hasher.write_u8(*b);
+                hasher.write_u8(*c);
+                record(hasher.finish());
+                cases += 1;
+            }
+        }
+    }
+    for start in 0..63 {
+        for stride in 1..=63 {
+            for count in 4..=63 {
+                let mut hasher = crc32fast::Hasher::new_with_initial(seed);
+                for i in 0..count {
+                    let j = (start + i*stride) % 63;
+                    hasher.write_u8(ALPHANUMS[j]);
+                }
+                record(hasher.finish());
+                cases += 1;
+            }
+        }
+    }
+    println!("unique hashes: {} / {} (32-bit: {})", hashes.len(), cases, hashes_32bit.len());
+    0
+}