QCryptographicHash: Add a static method to retrieve hash length

It's useful when you need to check how long a hash will be without first
generating one.

[ChangeLog][QtCore][QCryptographicHash] Add a static method, hashLength,
which returns the length of the output of a hash function in bytes.

Change-Id: Id6a454016523de83d157fd95c50105c6db4bb1d9
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

2 files changed, 41 insertions, 0 deletions

diff --git a/src/corelib/tools/qcryptographichash.cpp b/src/corelib/tools/qcryptographichash.cpp
index a1b121f1ee..3c79bb797d 100644
--- a/src/corelib/tools/qcryptographichash.cpp
+++ b/src/corelib/tools/qcryptographichash.cpp
@@ -544,6 +544,46 @@ QByteArray QCryptographicHash::hash(const QByteArray &data, Algorithm method)
     return hash.result();
 }
 
+/*!
+  Returns the size of the output of the selected hash \a method in bytes.
+
+  \since 5.12
+*/
+int QCryptographicHash::hashLength(QCryptographicHash::Algorithm method)
+{
+    switch (method) {
+    case QCryptographicHash::Sha1:
+        return 20;
+#ifndef QT_CRYPTOGRAPHICHASH_ONLY_SHA1
+    case QCryptographicHash::Md4:
+        return 16;
+    case QCryptographicHash::Md5:
+        return 16;
+    case QCryptographicHash::Sha224:
+        return SHA224HashSize;
+    case QCryptographicHash::Sha256:
+        return SHA256HashSize;
+    case QCryptographicHash::Sha384:
+        return SHA384HashSize;
+    case QCryptographicHash::Sha512:
+        return SHA512HashSize;
+    case QCryptographicHash::RealSha3_224:
+    case QCryptographicHash::Keccak_224:
+        return 224 / 8;
+    case QCryptographicHash::RealSha3_256:
+    case QCryptographicHash::Keccak_256:
+        return 256 / 8;
+    case QCryptographicHash::RealSha3_384:
+    case QCryptographicHash::Keccak_384:
+        return 384 / 8;
+    case QCryptographicHash::RealSha3_512:
+    case QCryptographicHash::Keccak_512:
+        return 512 / 8;
+#endif
+    }
+    return 0;
+}
+
 QT_END_NAMESPACE
 
 #ifndef QT_NO_QOBJECT
diff --git a/src/corelib/tools/qcryptographichash.h b/src/corelib/tools/qcryptographichash.h
index 2f74d42405..ad1de7c756 100644
--- a/src/corelib/tools/qcryptographichash.h
+++ b/src/corelib/tools/qcryptographichash.h
@@ -101,6 +101,7 @@ public:
     QByteArray result() const;
 
     static QByteArray hash(const QByteArray &data, Algorithm method);
+    static int hashLength(Algorithm method);
 private:
     Q_DISABLE_COPY(QCryptographicHash)
     QCryptographicHashPrivate *d;