Rename variables and update comments in mpi_core_add_if test

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/tests/suites/test_suite_mpi.function b/tests/suites/test_suite_mpi.function
index 7ca21fa..32e08a9 100644
--- a/tests/suites/test_suite_mpi.function
+++ b/tests/suites/test_suite_mpi.function
@@ -1721,23 +1721,23 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mpi_core_add_if( char * input_l, char * input_r,
+void mpi_core_add_if( char * input_A, char * input_B,
                       char * input_X4, int carry4,
                       char * input_X8, int carry8 )
 {
-    mbedtls_mpi X4, X8, l, r;
-    mbedtls_mpi_uint *la = NULL;
-    mbedtls_mpi_uint *ra = NULL;
-    mbedtls_mpi_uint *Xa = NULL;
-    mbedtls_mpi_uint *da = NULL;
+    mbedtls_mpi X4, X8, A, B;
+    mbedtls_mpi_uint *a = NULL; /* first value to add */
+    mbedtls_mpi_uint *b = NULL; /* second value to add */
+    mbedtls_mpi_uint *x = NULL; /* expected */
+    mbedtls_mpi_uint *d = NULL; /* destination - the in/out first op */
 
+    mbedtls_mpi_init( &A );
+    mbedtls_mpi_init( &B );
     mbedtls_mpi_init( &X4 );
     mbedtls_mpi_init( &X8 );
-    mbedtls_mpi_init( &l );
-    mbedtls_mpi_init( &r );
 
-    TEST_EQUAL( 0, mbedtls_test_read_mpi( &l, input_l ) );
-    TEST_EQUAL( 0, mbedtls_test_read_mpi( &r, input_r ) );
+    TEST_EQUAL( 0, mbedtls_test_read_mpi( &A, input_A ) );
+    TEST_EQUAL( 0, mbedtls_test_read_mpi( &B, input_B ) );
     TEST_EQUAL( 0, mbedtls_test_read_mpi( &X4, input_X4 ) );
     TEST_EQUAL( 0, mbedtls_test_read_mpi( &X8, input_X8 ) );
 
@@ -1748,71 +1748,81 @@
     mbedtls_mpi_uint carry = ( sizeof(mbedtls_mpi_uint) == 4 ) ? carry4 : carry8;
 
     /* All of the inputs are +ve (or zero) */
-    TEST_EQUAL( 1, l.s );
-    TEST_EQUAL( 1, r.s );
+    TEST_EQUAL( 1, A.s );
+    TEST_EQUAL( 1, B.s );
     TEST_EQUAL( 1, X->s );
 
-    /* Test cases are such that l <= r, so #limbs should be <= */
-    TEST_ASSERT( l.n <= r.n );
-    TEST_ASSERT( X->n <= r.n );
+    /* Test cases are such that A <= B, so #limbs should be <= */
+    TEST_ASSERT( A.n <= B.n );
+    TEST_ASSERT( X->n <= B.n );
 
     /* Now let's get arrays of mbedtls_mpi_uints, rather than MPI structures */
-    la = mbedtls_calloc( r.n, sizeof(mbedtls_mpi_uint) );
-    ra = mbedtls_calloc( r.n, sizeof(mbedtls_mpi_uint) );
-    Xa = mbedtls_calloc( r.n, sizeof(mbedtls_mpi_uint) );
-    da = mbedtls_calloc( r.n, sizeof(mbedtls_mpi_uint) );
 
-    size_t bytes = r.n * sizeof(mbedtls_mpi_uint);
+    /* mbedtls_mpi_core_add_if() uses input arrays of mbedtls_mpi_uints which
+     * must be the same size. The MPIs we've read in will only have arrays
+     * large enough for the number they represent. Therefore we create new
+     * raw arrays of mbedtls_mpi_uints and populate them from the MPIs we've
+     * just read in.
+     *
+     * We generated test data such that B was always >= A, so that's how many
+     * limbs each of these need.
+     */
+    a = mbedtls_calloc( B.n, sizeof(mbedtls_mpi_uint) );
+    b = mbedtls_calloc( B.n, sizeof(mbedtls_mpi_uint) );
+    x = mbedtls_calloc( B.n, sizeof(mbedtls_mpi_uint) );
+    d = mbedtls_calloc( B.n, sizeof(mbedtls_mpi_uint) );
 
-    TEST_ASSERT( la != NULL );
-    TEST_ASSERT( ra != NULL );
-    TEST_ASSERT( Xa != NULL );
-    TEST_ASSERT( da != NULL );
+    size_t bytes = B.n * sizeof(mbedtls_mpi_uint);
+
+    TEST_ASSERT( a != NULL );
+    TEST_ASSERT( b != NULL );
+    TEST_ASSERT( x != NULL );
+    TEST_ASSERT( d != NULL );
 
     /* Populate the arrays. As the mbedtls_mpi_uint[]s in mbedtls_mpis (and as
      * processed by mbedtls_mpi_core_add_if()) are little endian, we can just
      * copy what we have as long as MSBs are 0 (which they are from calloc())
      */
-    memcpy( la, l.p, l.n * sizeof(mbedtls_mpi_uint) );
-    memcpy( ra, r.p, r.n * sizeof(mbedtls_mpi_uint) );
-    memcpy( Xa, X->p, X->n * sizeof(mbedtls_mpi_uint) );
+    memcpy( a, A.p, A.n * sizeof(mbedtls_mpi_uint) );
+    memcpy( b, B.p, B.n * sizeof(mbedtls_mpi_uint) );
+    memcpy( x, X->p, X->n * sizeof(mbedtls_mpi_uint) );
 
-    /* 1a) a += b, cond = 0 => there should be no carry */
-    memcpy( da, la, r.n * sizeof(mbedtls_mpi_uint) );
-    TEST_EQUAL( 0, mbedtls_mpi_core_add_if( da, ra, r.n, 0 ) );
+    /* 1a) a + b: d = a; d += b, cond = 0 => there should be no carry */
+    memcpy( d, a, bytes );
+    TEST_EQUAL( 0, mbedtls_mpi_core_add_if( d, b, B.n, 0 ) );
 
-    /* 1b) and a should be unchanged */
-    ASSERT_COMPARE( da, bytes, la, bytes );
+    /* 1b) and d should be unchanged */
+    ASSERT_COMPARE( d, bytes, a, bytes );
 
-    /* 2a) a += b, cond = 1 => we should get the correct carry */
-    TEST_EQUAL( carry, mbedtls_mpi_core_add_if( da, ra, r.n, 1 ) );
+    /* 2a) a + b: d = a; d += b, cond = 1 => we should get the correct carry */
+    TEST_EQUAL( carry, mbedtls_mpi_core_add_if( d, b, B.n, 1 ) );
 
-    /* 2b) and a should have the correct result */
-    ASSERT_COMPARE( da, bytes, Xa, bytes );
+    /* 2b) and d should have the correct result */
+    ASSERT_COMPARE( d, bytes, x, bytes );
 
-    /* 3a) b += a, cond = 0 => there should be no carry */
-    memcpy( da, ra, r.n * sizeof(mbedtls_mpi_uint) );
-    TEST_EQUAL( 0, mbedtls_mpi_core_add_if( da, la, r.n, 0 ) );
+    /* 3a) b + a: d = b; d += a, cond = 0 => there should be no carry */
+    memcpy( d, b, bytes );
+    TEST_EQUAL( 0, mbedtls_mpi_core_add_if( d, a, B.n, 0 ) );
 
-    /* 3b) and b should be unchanged */
-    ASSERT_COMPARE( da, bytes, ra, bytes );
+    /* 3b) and d should be unchanged */
+    ASSERT_COMPARE( d, bytes, b, bytes );
 
-    /* 4a) b += a, cond = 1 => we should get the correct carry */
-    TEST_EQUAL( carry, mbedtls_mpi_core_add_if( da, la, r.n, 1 ) );
+    /* 4a) b + a: d = b; d += a, cond = 1 => we should get the correct carry */
+    TEST_EQUAL( carry, mbedtls_mpi_core_add_if( d, a, B.n, 1 ) );
 
-    /* 4b) and b should have the correct result */
-    ASSERT_COMPARE( da, bytes, Xa, bytes );
+    /* 4b) and d should have the correct result */
+    ASSERT_COMPARE( d, bytes, x, bytes );
 
 exit:
-    mbedtls_free( la );
-    mbedtls_free( ra );
-    mbedtls_free( Xa );
-    mbedtls_free( da );
+    mbedtls_free( a );
+    mbedtls_free( b );
+    mbedtls_free( x );
+    mbedtls_free( d );
 
     mbedtls_mpi_free( &X4 );
     mbedtls_mpi_free( &X8 );
-    mbedtls_mpi_free( &l );
-    mbedtls_mpi_free( &r );
+    mbedtls_mpi_free( &A );
+    mbedtls_mpi_free( &B );
 }
 /* END_CASE */