get_random_num: Simplify

random() is available everywhere except Windows and DOS.
Also switch Windows to rand_s.

src/Makefile

@@ -250,11 +250,13 @@ CFLAGS_CROSS_WIN32      += -I$(OPENCL_HEADERS_KHRONOS)/
 CFLAGS_CROSS_WIN32      += -I$(WIN_ICONV_32)/include/
 CFLAGS_CROSS_WIN32      += -m32
 CFLAGS_CROSS_WIN32      += -DWITH_HWMON
+CFLAGS_CROSS_WIN32      += -D_CRT_RAND_S
 CFLAGS_CROSS_WIN64      := $(CFLAGS)
 CFLAGS_CROSS_WIN64      += -I$(OPENCL_HEADERS_KHRONOS)/
 CFLAGS_CROSS_WIN64      += -I$(WIN_ICONV_64)/include/
 CFLAGS_CROSS_WIN64      += -m64
 CFLAGS_CROSS_WIN64      += -DWITH_HWMON
+CFLAGS_CROSS_WIN64      += -D_CRT_RAND_S
 
 LFLAGS_CROSS_LINUX32    := $(LFLAGS)
 LFLAGS_CROSS_LINUX32    += -lpthread

src/shared.c

@@ -379,27 +379,16 @@ u32 get_random_num (const u32 min, const u32 max)
 
   if (low == 0) return (0);
 
-  #if defined (__linux__)
-
-  u32 data;
-
-  FILE *fp = fopen ("/dev/urandom", "rb");
-
-  if (fp == NULL) return (0);
-
-  const int nread = fread (&data, sizeof (u32), 1, fp);
-
-  fclose (fp);
-
-  if (nread != 1) return 0;
+  #if defined (_WIN)
 
-  u64 r = data % low; r += min;
+  u32 r;
+  rand_s(&r);
 
-  return (u32) r;
+  return ((r % (max - min)) + min);
 
   #else
 
-  return (((u32) rand () % (max - min)) + min);
+  return (((u32) random () % (max - min)) + min);
 
   #endif
 }