std/hash: add generic tests for idempotency/iterative api

1 files changed, 27 insertions, 0 deletions

diff --git a/lib/std/hash/verify.zig b/lib/std/hash/verify.zig
index bfc6a1f22c..5d853fee28 100644
--- a/lib/std/hash/verify.zig
+++ b/lib/std/hash/verify.zig
@@ -13,6 +13,15 @@ fn hashMaybeSeed(comptime hash_fn: anytype, seed: anytype, buf: []const u8) @typ
     }
 }
 
+fn initMaybeSeed(comptime Hash: anytype, seed: anytype) Hash {
+    const HashFn = @typeInfo(@TypeOf(Hash.init)).Fn;
+    if (HashFn.params.len == 1) {
+        return Hash.init(@intCast(seed));
+    } else {
+        return Hash.init();
+    }
+}
+
 // Returns a verification code, the same as user by SMHasher.
 //
 // Hash keys of the form {0}, {0,1}, {0,1,2}... up to N=255, using 256-N as seed.
@@ -33,3 +42,21 @@ pub fn smhasher(comptime hash_fn: anytype) u32 {
 
     return @truncate(hashMaybeSeed(hash_fn, 0, buf_all[0..]));
 }
+
+pub fn iterativeApi(comptime Hash: anytype) !void {
+    // Sum(1..32) = 528
+    var buf: [528]u8 = [_]u8{0} ** 528;
+    var len: usize = 0;
+    const seed = 0;
+
+    var hasher = initMaybeSeed(Hash, seed);
+    for (1..32) |i| {
+        const r = hashMaybeSeed(Hash.hash, seed, buf[0 .. len + i]);
+        hasher.update(buf[len..][0..i]);
+        const f1 = hasher.final();
+        const f2 = hasher.final();
+        if (f1 != f2) return error.IterativeHashWasNotIdempotent;
+        if (f1 != r) return error.IterativeHashDidNotMatchDirect;
+        len += i;
+    }
+}