Add s_mp_cmpexch_n()

To be able to support this for MSVC as well, we have to move this into a
separate private API function.

Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>

Author: sjaeckel

s_mp_cmpexch_n.c

@@ -0,0 +1,43 @@
+#include "tommath_private.h"
+#ifdef S_MP_CMPEXCH_N_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+#ifdef __GNUC__
+#define S_CMPEXCH_N_GCC_C
+bool s_cmpexch_n_gcc(void **ptr, void **expected, void *desired)
+{
+   return __atomic_compare_exchange_n(ptr, expected, desired, true, __ATOMIC_ACQ_REL, __ATOMIC_ACQUIRE);
+}
+#endif
+
+#ifdef _MSC_VER
+#define S_CMPEXCH_N_MSVC_C
+
+#ifndef _WIN32_WINNT
+#define _WIN32_WINNT 0x0501
+#endif
+#ifndef WINVER
+#define WINVER 0x0501
+#endif
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+bool s_cmpexch_n_msvc(void **ptr, void **expected, void *desired)
+{
+   return InterlockedCompareExchangePointer(ptr, *(expected), desired) == desired;
+}
+#endif
+
+bool s_cmpexch_n_gcc(void **ptr, void **expected, void *desired);
+bool s_cmpexch_n_msvc(void **ptr, void **expected, void *desired);
+
+bool s_mp_cmpexch_n(void **ptr, void **expected, void *desired)
+{
+   if (MP_HAS(S_CMPEXCH_N_GCC)) return s_cmpexch_n_gcc(ptr, expected, desired);
+   if (MP_HAS(S_CMPEXCH_N_MSVC)) return s_cmpexch_n_msvc(ptr, expected, desired);
+   return false;
+}
+
+#endif

s_mp_warray_get.c

@@ -15,7 +15,7 @@ void *s_mp_warray_get(void)
       if (s_mp_warray.l_free[n].warray == NULL)
          continue;
       ret = s_mp_warray.l_free[n].warray;
-      if (MP_CMPEXCH(&s_mp_warray.l_free[n].warray, &ret, NULL)) {
+      if (s_mp_cmpexch_n(&s_mp_warray.l_free[n].warray, &ret, NULL)) {
          s_mp_warray.l_used[n].warray = ret;
          goto LBL_OUT;
       }

tommath_class.h

@@ -136,6 +136,7 @@
 #   define MP_XOR_C
 #   define MP_ZERO_C
 #   define S_MP_ADD_C
+#   define S_MP_CMPEXCH_N_C
 #   define S_MP_COPY_DIGS_C
 #   define S_MP_DIV_3_C
 #   define S_MP_DIV_RECURSIVE_C
@@ -986,6 +987,9 @@
 #   define S_MP_ZERO_DIGS_C
 #endif
 
+#if defined(S_MP_CMPEXCH_N_C)
+#endif
+
 #if defined(S_MP_COPY_DIGS_C)
 #endif
 
@@ -1309,6 +1313,7 @@
 
 #if defined(S_MP_WARRAY_GET_C)
 #   define MP_WARRAY_INIT_C
+#   define S_MP_CMPEXCH_N_C
 #endif
 
 #if defined(S_MP_WARRAY_PUT_C)

tommath_private.h

@@ -104,10 +104,6 @@ extern void *MP_CALLOC(size_t nmemb, size_t size);
 extern void MP_FREE(void *mem, size_t size);
 #endif
 
-#ifndef MP_CMPEXCH
-#define MP_CMPEXCH(ptr, expected, desired) __atomic_compare_exchange_n(ptr, expected, desired, true, __ATOMIC_ACQ_REL, __ATOMIC_ACQUIRE)
-#endif
-
 /* feature detection macro */
 #ifdef _MSC_VER
 /* Prevent false positive: not enough arguments for function-like macro invocation */
@@ -238,6 +234,8 @@ MP_PRIVATE mp_err s_mp_radix_size_overestimate(const mp_int *a, const int radix,
 MP_PRIVATE mp_err s_mp_fp_log(const mp_int *a, mp_int *c) MP_WUR;
 MP_PRIVATE mp_err s_mp_fp_log_d(const mp_int *a, mp_word *c) MP_WUR;
 
+MP_PRIVATE bool s_mp_cmpexch_n(void **ptr, void **expected, void *desired);
+
 #ifdef MP_SMALL_STACK_SIZE
 #define MP_SMALL_STACK_SIZE_C
 #define MP_ALLOC_WARRAY(name) *name = s_mp_warray_get()