switch C code prefix to NIF

src/Nitload.Native/nif-src/s.factorial.x86.c

@@ -0,0 +1,33 @@
+#include "nif_target.h"
+
+#if NIF_IS_ARCH(NIF_ARCH_X86_64)
+
+#include "nif_internal.h"
+#include "nif_intrinsic.h"
+
+static __m128i facIncrement;
+static __m128i facBase;
+
+INTERNAL uint64_t NIF_DECL factorial_simd_sse(int n)
+{
+        facIncrement = _mm_set1_epi32(4);
+        facBase = _mm_setr_epi32(1, 2, 3, 4);
+        __m128i baseResult = facBase;
+        __m128i facBaseLocal = facBase;
+        const int cycle = (n - 3) >> 2;
+        const uint32_t rest = (cycle << 2) + 1;
+        for (size_t i = 0; i < cycle; i++) {
+                facBaseLocal = _mm_add_epi32(facBaseLocal, facIncrement);
+                baseResult = _mm_mullo_epi32(baseResult, facBaseLocal);
+        }
+        NIF_ALIGNAS(16) int32_t lanes[4];
+        _mm_store_si128((__m128i *)lanes, baseResult);
+        uint64_t result = (uint64_t)lanes[0] * (uint64_t)lanes[1] * (uint64_t)lanes[2] *
+                          (uint64_t)lanes[3];
+        for (uint64_t i = rest; i < n; i++) {
+                result *= i;
+        }
+        return result;
+}
+
+#endif