Remove string hack for mbedtls_mpi_mod_int testing

Now that the test framework can pass arbitrary values of type
mbedtls_mpi_sint, just do that.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_bignum.function b/tests/suites/test_suite_bignum.function
index 2f00ff8..7f858e5 100644
--- a/tests/suites/test_suite_bignum.function
+++ b/tests/suites/test_suite_bignum.function
@@ -923,47 +923,16 @@
 /* END_CASE */
 
 /* BEGIN_CASE */
-void mpi_mod_int(char *input_X, char *input_Y,
-                 char *input_A, int mod_result)
+void mpi_mod_int(char *input_X, mbedtls_mpi_sint y,
+                 mbedtls_mpi_sint a, int mod_result)
 {
     mbedtls_mpi X;
-    mbedtls_mpi Y;
-    mbedtls_mpi A;
     int res;
     mbedtls_mpi_uint r;
 
     mbedtls_mpi_init(&X);
-    mbedtls_mpi_init(&Y);
-    mbedtls_mpi_init(&A);
 
-    /* We use MPIs to read Y and A since the test framework limits us to
-     * ints, so we can't have 64-bit values */
     TEST_EQUAL(mbedtls_test_read_mpi(&X, input_X), 0);
-    TEST_EQUAL(mbedtls_test_read_mpi(&Y, input_Y), 0);
-    TEST_EQUAL(mbedtls_test_read_mpi(&A, input_A), 0);
-
-    TEST_EQUAL(Y.n, 1);
-    TEST_EQUAL(A.n, 1);
-
-    /* Convert the MPIs for Y and A to (signed) mbedtls_mpi_sints */
-
-    /* Since we're converting sign+magnitude to two's complement, we lose one
-     * bit of value in the output. This means there are some values we can't
-     * represent, e.g. (hex) -A0000000 on 32-bit systems. These are technically
-     * invalid test cases, so could be considered "won't happen", but they are
-     * easy to test for, and this helps guard against human error. */
-
-    mbedtls_mpi_sint y = (mbedtls_mpi_sint) Y.p[0];
-    TEST_ASSERT(y >= 0);        /* If y < 0 here, we can't make negative y */
-    if (Y.s == -1) {
-        y = -y;
-    }
-
-    mbedtls_mpi_sint a = (mbedtls_mpi_sint) A.p[0];
-    TEST_ASSERT(a >= 0);        /* Same goes for a */
-    if (A.s == -1) {
-        a = -a;
-    }
 
     res = mbedtls_mpi_mod_int(&r, &X, y);
     TEST_EQUAL(res, mod_result);
@@ -973,8 +942,6 @@
 
 exit:
     mbedtls_mpi_free(&X);
-    mbedtls_mpi_free(&Y);
-    mbedtls_mpi_free(&A);
 }
 /* END_CASE */
 
diff --git a/tests/suites/test_suite_bignum.misc.data b/tests/suites/test_suite_bignum.misc.data
index 11c5d7b..9d068f1 100644
--- a/tests/suites/test_suite_bignum.misc.data
+++ b/tests/suites/test_suite_bignum.misc.data
@@ -1229,45 +1229,45 @@
 mpi_mod_mpi:"-":"-2a":"":MBEDTLS_ERR_MPI_NEGATIVE_VALUE
 
 Base test mbedtls_mpi_mod_int #1
-mpi_mod_int:"3e8":"d":"c":0
+mpi_mod_int:"3e8":0xd:0xc:0
 
 Base test mbedtls_mpi_mod_int #2 (Divide by zero)
-mpi_mod_int:"3e8":"0":"0":MBEDTLS_ERR_MPI_DIVISION_BY_ZERO
+mpi_mod_int:"3e8":0x0:0x0:MBEDTLS_ERR_MPI_DIVISION_BY_ZERO
 
 Base test mbedtls_mpi_mod_int #3
-mpi_mod_int:"-3e8":"d":"1":0
+mpi_mod_int:"-3e8":0xd:0x1:0
 
 Base test mbedtls_mpi_mod_int #4 (Negative modulo)
-mpi_mod_int:"3e8":"-d":"0":MBEDTLS_ERR_MPI_NEGATIVE_VALUE
+mpi_mod_int:"3e8":-0xd:0x0:MBEDTLS_ERR_MPI_NEGATIVE_VALUE
 
 Base test mbedtls_mpi_mod_int #5 (Negative modulo)
-mpi_mod_int:"-3e8":"-d":"0":MBEDTLS_ERR_MPI_NEGATIVE_VALUE
+mpi_mod_int:"-3e8":-0xd:0x0:MBEDTLS_ERR_MPI_NEGATIVE_VALUE
 
 Base test mbedtls_mpi_mod_int #6 (By 1)
-mpi_mod_int:"3e8":"1":"0":0
+mpi_mod_int:"3e8":0x1:0x0:0
 
 Base test mbedtls_mpi_mod_int #7 (By 2)
-mpi_mod_int:"3e9":"2":"1":0
+mpi_mod_int:"3e9":0x2:0x1:0
 
 Base test mbedtls_mpi_mod_int #8 (By 2)
-mpi_mod_int:"3e8":"2":"0":0
+mpi_mod_int:"3e8":0x2:0x0:0
 
 Test mbedtls_mpi_mod_int: 0 (null) % 1
-mpi_mod_int:"":"1":"0":0
+mpi_mod_int:"":0x1:0x0:0
 
 Test mbedtls_mpi_mod_int: 0 (null) % 2
-mpi_mod_int:"":"2":"0":0
+mpi_mod_int:"":0x2:0x0:0
 
 Test mbedtls_mpi_mod_int: 0 (null) % -1
-mpi_mod_int:"":"-1":"0":MBEDTLS_ERR_MPI_NEGATIVE_VALUE
+mpi_mod_int:"":-0x1:0x0:MBEDTLS_ERR_MPI_NEGATIVE_VALUE
 
 Test mbedtls_mpi_mod_int: 0 (null) % -2
-mpi_mod_int:"":"-2":"0":MBEDTLS_ERR_MPI_NEGATIVE_VALUE
+mpi_mod_int:"":-0x2:0x0:MBEDTLS_ERR_MPI_NEGATIVE_VALUE
 
 # CURRENTLY FAILS - SEE GITHUB ISSUE #6540
 #Test mbedtls_mpi_mod_int: 230772460340063000000100500000300000010 % 5178236083361335880 -> 3386266129388798810
 #depends_on:MBEDTLS_HAVE_INT64
-#mpi_mod_int:"AD9D28BF6C4E98FDF156BF0980CEE30A":"47DCCA4847DCCA48":"2EFE6F1A7D28035A":0
+#mpi_mod_int:"AD9D28BF6C4E98FDF156BF0980CEE30A":0x47DCCA4847DCCA48:0x2EFE6F1A7D28035A:0
 
 Test mbedtls_mpi_mod_mpi: 230772460340063000000100500000300000010 % 5178236083361335880 -> 3386266129388798810
 mpi_mod_mpi:"AD9D28BF6C4E98FDF156BF0980CEE30A":"47DCCA4847DCCA48":"2EFE6F1A7D28035A":0
@@ -1275,7 +1275,7 @@
 # CURRENTLY FAILS - SEE GITHUB ISSUE #6540
 #Test mbedtls_mpi_mod_int: 230772460340062999996714233870911201200 % 5178236083361335880 -> 0
 #depends_on:MBEDTLS_HAVE_INT64
-#mpi_mod_int:"AD9D28BF6C4E98FDC2584FEF03A6DFB0":"47DCCA4847DCCA48":"0":0
+#mpi_mod_int:"AD9D28BF6C4E98FDC2584FEF03A6DFB0":0x47DCCA4847DCCA48:0x0:0
 
 Test mbedtls_mpi_mod_mpi: 230772460340062999996714233870911201200 % 5178236083361335880 -> 0
 mpi_mod_mpi:"AD9D28BF6C4E98FDC2584FEF03A6DFB0":"47DCCA4847DCCA48":"0":0
@@ -1283,7 +1283,7 @@
 # CURRENTLY FAILS WHEN MPIS ARE 32-BIT (ISSUE #6450): WHEN FIXED, REMOVE "depends_on" LINE
 Test mbedtls_mpi_mod_int: 230772460340063000000100500000300000010 % 1205652040 -> 3644370
 depends_on:MBEDTLS_HAVE_INT64
-mpi_mod_int:"AD9D28BF6C4E98FDF156BF0980CEE30A":"47DCCA48":"379BD2":0
+mpi_mod_int:"AD9D28BF6C4E98FDF156BF0980CEE30A":0x47DCCA48:0x379BD2:0
 
 Test mbedtls_mpi_mod_mpi: 230772460340063000000100500000300000010 % 1205652040 -> 3644370
 mpi_mod_mpi:"AD9D28BF6C4E98FDF156BF0980CEE30A":"47DCCA48":"379BD2":0
@@ -1291,7 +1291,7 @@
 # CURRENTLY FAILS WHEN MPIS ARE 32-BIT (ISSUE #6450): WHEN FIXED, REMOVE "depends_on" LINE
 Test mbedtls_mpi_mod_int: 230772460340063000000100500000296355640 % 1205652040 -> 0
 depends_on:MBEDTLS_HAVE_INT64
-mpi_mod_int:"AD9D28BF6C4E98FDF156BF0980974738":"47DCCA48":"0":0
+mpi_mod_int:"AD9D28BF6C4E98FDF156BF0980974738":0x47DCCA48:0x0:0
 
 Test mbedtls_mpi_mod_mpi: 230772460340063000000100500000296355640 % 1205652040 -> 0
 mpi_mod_mpi:"AD9D28BF6C4E98FDF156BF0980974738":"47DCCA48":"0":0