Use int64_t for KLU_INDEXTYPE if SUNDIALS_INT64_T is true. (#477)

`long int` is 32 bits wide on systems that use an LLP64 data model
(e.g., Windows). Use a type for which the C standard guarantees that it
is 64-bit instead (i.e., `int64_t`).

See the error in CI for PR #432.

Signed-off-by: Markus Mützel <markus.muetzel@gmx.de>
Co-authored-by: Cody Balos <balos1@llnl.gov>

CHANGELOG.md

@@ -65,6 +65,9 @@ Fixed a CMake bug that caused an MPI linking error for our C++ examples in some
 Fixed a bug in `ARKodeSPRKTable_Create` where the coefficient arrays where not
 allocated.
 
+Fix bug on LLP64 platforms (like Windows 64-bit) where `KLU_INDEXTYPE` could be
+32 bits wide even if `SUNDIALS_INT64_T` is defined.
+
 ## Changes to SUNDIALS in release v7.0.0
 
 ### Major Feature

doc/shared/RecentChanges.rst

@@ -65,3 +65,6 @@ Fixed a CMake bug that caused an MPI linking error for our C++ examples in some
 
 Fixed a bug in :c:func:`ARKodeSPRKTable_Create` where the coefficient arrays
 where not allocated.
+
+Fix bug on LLP64 platforms (like Windows 64-bit) where ``KLU_INDEXTYPE`` could be
+32 bits wide even if ``SUNDIALS_INT64_T`` is defined.

src/sunlinsol/klu/sunlinsol_klu.c

@@ -16,6 +16,7 @@
  * the SUNLINSOL package.
  * -----------------------------------------------------------------*/
 
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sundials/sundials_math.h>
@@ -49,7 +50,7 @@
  */
 
 #if defined(SUNDIALS_INT64_T)
-#define KLU_INDEXTYPE long int
+#define KLU_INDEXTYPE int64_t
 #else
 #define KLU_INDEXTYPE int
 #endif