rename the "context string" to the "purpose string"purpose_string

Apart from being pretty ambiguous in general, the term "context string"
has the specific problem that it isn't clear whether it should be
describing the input or the output. In fact, it's quite important that
it describes the output, because the whole point is to domain-separate
different outputs that derive from the *same* input. To make that
clearer, rename the "context string" to the "purpose string" in
documentation.

1 files changed, 4 insertions, 4 deletions

diff --git a/c/blake3_c_rust_bindings/src/test.rs b/c/blake3_c_rust_bindings/src/test.rs
index b989ae9..81b3abe 100644
--- a/c/blake3_c_rust_bindings/src/test.rs
+++ b/c/blake3_c_rust_bindings/src/test.rs
@@ -390,21 +390,21 @@ fn test_compare_reference_impl() {
 
         // derive_key
         {
-            let context = "BLAKE3 2019-12-27 16:13:59 example context (not the test vector one)";
-            let mut reference_hasher = reference_impl::Hasher::new_derive_key(context);
+            let purpose = "BLAKE3 2019-12-27 16:13:59 example context (not the test vector one)";
+            let mut reference_hasher = reference_impl::Hasher::new_derive_key(purpose);
             reference_hasher.update(input);
             let mut expected_out = [0; OUT];
             reference_hasher.finalize(&mut expected_out);
 
             // the regular C string API
-            let mut test_hasher = crate::Hasher::new_derive_key(context);
+            let mut test_hasher = crate::Hasher::new_derive_key(purpose);
             test_hasher.update(input);
             let mut test_out = [0; OUT];
             test_hasher.finalize(&mut test_out);
             assert_eq!(test_out[..], expected_out[..]);
 
             // the raw bytes API
-            let mut test_hasher_raw = crate::Hasher::new_derive_key_raw(context.as_bytes());
+            let mut test_hasher_raw = crate::Hasher::new_derive_key_raw(purpose.as_bytes());
             test_hasher_raw.update(input);
             let mut test_out_raw = [0; OUT];
             test_hasher_raw.finalize(&mut test_out_raw);