ENH: remove sign from SHA1Digest cdata_bytes(), data_bytes()

- this refinement of commit 81807646ca makes these methods
  consistent with other objects/containers.

  The 'unsigned char' access is still available via cdata()

applications/test/parallel-comm2/Test-parallel-comm2.C

@@ -261,11 +261,11 @@ int main(int argc, char *argv[])
         }
 
         {
-            const SHA1Digest myHostDigest(SHA1(hostName()).digest());
+            const SHA1Digest myDigest(SHA1(hostName()).digest());
 
             UPstream::mpiGather
             (
-                reinterpret_cast<const char*>(myHostDigest.cdata_bytes()),
+                myDigest.cdata_bytes(),     // Send
                 SHA1Digest::max_size(),     // Num send per proc
                 digests.data_bytes(),       // Recv
                 SHA1Digest::max_size(),     // Num recv per proc

src/OpenFOAM/db/IOstreams/Pstreams/UPstream.C

@@ -88,11 +88,9 @@ static List<int> getHostGroupIds(const label parentCommunicator)
     SHA1Digest myDigest(SHA1(hostName()).digest());
 
     // The fixed-length digest allows use of MPI_Gather
-    // and avoids Pstream::gatherList() during setup...
-
     UPstream::mpiGather
     (
-        reinterpret_cast<const char*>(myDigest.cdata_bytes()),
+        myDigest.cdata_bytes(),     // Send
         SHA1Digest::max_size(),     // Num send per proc
         digests.data_bytes(),       // Recv
         SHA1Digest::max_size(),     // Num recv per proc

src/OpenFOAM/primitives/hashes/SHA1/SHA1Digest.H

@@ -128,16 +128,19 @@ public:
         //- Raw digest data (20 bytes) - const access
         const unsigned char* cdata() const noexcept { return dig_.data(); }
 
-        //- Raw digest data (20 bytes) - const access
+        //- Raw digest char data (20 bytes) - const access.
-        const unsigned char* cdata_bytes() const noexcept
+        //- For consistency with other objects, these are \em not unsigned.
+        const char* cdata_bytes() const noexcept
         {
-            return dig_.data();
+            return reinterpret_cast<const char*>(dig_.data());
         }
 
-        //- Raw digest data (20 bytes) - non-const access. Use with caution!
+        //- Raw digest char data (20 bytes) - non-const access.
-        unsigned char* data_bytes() noexcept
+        //- For consistency with other objects, these are \em not unsigned.
+        //- Use with caution - generally for broadcasting only.
+        char* data_bytes() noexcept
         {
-            return dig_.data();
+            return reinterpret_cast<char*>(dig_.data());
         }
 
         //- The number of bytes in digest (20)