Overhaul testing of mbedtls_mpi_copy

Replace the two test functions mbedtls_mpi_copy_sint (supporting signed
inputs but always with exactly one limb) and mbedtls_mpi_copy_binary
(supporting arbitrary-sized inputs but not negative inputs) by a single
function that supports both arbitrary-sized inputs and arbitrary-signed
inputs. This will allows testing combinations like negative source and
zero-sized destination.

Also generalize mpi_copy_self to support arbitrary inputs.

Generate a new list of test cases systematically enumerating all
possibilities among various categories: zero with 0 or 1 limb, negative or
positive with 1 limb, negative or positive with >1 limb. I used the
following Perl script:

```
sub rhs { $_ = $_[0]; s/bead/beef/; s/ca5cadedb01dfaceacc01ade/face1e55ca11ab1ecab005e5/; $_ }
%v = (
    "zero (null)" => "",
    "zero (1 limb)" => "0",
    "small positive" => "bead",
    "large positive" => "ca5cadedb01dfaceacc01ade",
    "small negative" => "-bead",
    "large negative" => "-ca5cadedb01dfaceacc01ade",
);
foreach $s (sort keys %v) {
    foreach $d (sort keys %v) {
        printf "Copy %s to %s\nmbedtls_mpi_copy:\"%s\":\"%s\"\n\n",
               $s, $d, $v{$s}, rhs($v{$d});
    }
}
foreach $s (sort keys %v) {
    printf "Copy self: %s\nmpi_copy_self:\"%s\"\n\n", $s, $v{$s};
}
```

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index d45d3dc..42dbafa 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -501,56 +501,42 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mbedtls_mpi_copy_sint( int input_X, int input_Y )
+void mbedtls_mpi_copy( char *src_hex, char *dst_hex )
 {
-    mbedtls_mpi X, Y;
-    mbedtls_mpi_init( &X ); mbedtls_mpi_init( &Y );
+    mbedtls_mpi src, dst;
+    mbedtls_mpi_init( &src );
+    mbedtls_mpi_init( &dst );
 
-    TEST_ASSERT( mbedtls_mpi_lset( &X, input_X ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_lset( &Y, input_Y ) == 0 );
+    TEST_ASSERT( mbedtls_test_read_mpi( &src, 16, src_hex ) == 0 );
+    TEST_ASSERT( mbedtls_test_read_mpi( &dst, 16, dst_hex ) == 0 );
 
-    TEST_ASSERT( mbedtls_mpi_copy( &Y, &X ) == 0 );
-    TEST_ASSERT( sign_is_valid( &Y ) );
-    TEST_ASSERT( mbedtls_mpi_cmp_int( &X, input_X ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_cmp_int( &Y, input_X ) == 0 );
+    TEST_ASSERT( mbedtls_mpi_copy( &dst, &src ) == 0 );
+
+    TEST_ASSERT( sign_is_valid( &dst ) );
+    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &dst, &src ) == 0 );
 
 exit:
-    mbedtls_mpi_free( &X ); mbedtls_mpi_free( &Y );
+    mbedtls_mpi_free( &src );
+    mbedtls_mpi_free( &dst );
 }
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mbedtls_mpi_copy_binary( data_t *input_X, data_t *input_Y )
+void mpi_copy_self( char *input_X )
 {
-    mbedtls_mpi X, Y, X0;
-    mbedtls_mpi_init( &X ); mbedtls_mpi_init( &Y ); mbedtls_mpi_init( &X0 );
-
-    TEST_ASSERT( mbedtls_mpi_read_binary( &X, input_X->x, input_X->len ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_read_binary( &Y, input_Y->x, input_Y->len ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_read_binary( &X0, input_X->x, input_X->len ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &X, &X0 ) == 0 );
-
-    TEST_ASSERT( mbedtls_mpi_copy( &Y, &X ) == 0 );
-    TEST_ASSERT( sign_is_valid( &Y ) );
-    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &X, &X0 ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &Y, &X0 ) == 0 );
-
-exit:
-    mbedtls_mpi_free( &X ); mbedtls_mpi_free( &Y ); mbedtls_mpi_free( &X0 );
-}
-/* END_CASE */
-
-/* BEGIN_CASE */
-void mpi_copy_self( int input_X )
-{
-    mbedtls_mpi X;
+    mbedtls_mpi X, A;
+    mbedtls_mpi_init( &A );
     mbedtls_mpi_init( &X );
 
-    TEST_ASSERT( mbedtls_mpi_lset( &X, input_X ) == 0 );
+    TEST_ASSERT( mbedtls_test_read_mpi( &X, 16, input_X ) == 0 );
     TEST_ASSERT( mbedtls_mpi_copy( &X, &X ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_cmp_int( &X, input_X ) == 0 );
+
+    TEST_ASSERT( mbedtls_test_read_mpi( &A, 16, input_X ) == 0 );
+    TEST_ASSERT( sign_is_valid( &X ) );
+    TEST_ASSERT( mbedtls_mpi_cmp_mpi( &X, &A ) == 0 );
 
 exit:
+    mbedtls_mpi_free( &A );
     mbedtls_mpi_free( &X );
 }
 /* END_CASE */