minor: fix Secplus v1 time diff

include/compat_time.h

@@ -16,6 +16,15 @@
 #include <sys/time.h>
 #endif
 
+/** Subtract `struct timeval` values.
+
+    @param[out] result time difference result
+    @param x first time value
+    @param y second time value
+    @return 1 if the difference is negative, otherwise 0.
+*/
+int timeval_subtract(struct timeval *result, struct timeval *x, struct timeval *y);
+
 // platform-specific functions
 
 #ifdef _WIN32

src/compat_time.c

@@ -3,23 +3,13 @@
 // issue: <sys/time.h> is not available on Windows systems
 // solution: provide a compatible version for Windows systems
 
-#ifndef _WIN32
-// Linux variant
-
-// just so the compilation unit isn't empty
-int _compat_time(void)
-{
-    return 0;
-}
+#include "compat_time.h"
 
-#else
-// Windows variant
+#ifdef _WIN32
 
 #include <stdbool.h>
 #include <stddef.h>
 
-#include "compat_time.h"
-
 #if defined(_MSC_VER) || defined(_MSC_EXTENSIONS)
 #define DELTA_EPOCH_IN_MICROSECS 11644473600000000Ui64
 #else
@@ -43,4 +33,26 @@ int gettimeofday(struct timeval *tv, void *tz)
     return 0;
 }
 
-#endif // _WIN32 / !_WIN32
+#endif // _WIN32
+
+int timeval_subtract(struct timeval *result, struct timeval *x, struct timeval *y)
+{
+    // Perform the carry for the later subtraction by updating y
+    if (x->tv_usec < y->tv_usec) {
+        int nsec = (y->tv_usec - x->tv_usec) / 1000000 + 1;
+        y->tv_usec -= 1000000 * nsec;
+        y->tv_sec += nsec;
+    }
+    if (x->tv_usec - y->tv_usec > 1000000) {
+        int nsec = (x->tv_usec - y->tv_usec) / 1000000;
+        y->tv_usec += 1000000 * nsec;
+        y->tv_sec -= nsec;
+    }
+
+    // Compute the time difference, tv_usec is certainly positive
+    result->tv_sec  = x->tv_sec - y->tv_sec;
+    result->tv_usec = x->tv_usec - y->tv_usec;
+
+    // Return 1 if result is negative
+    return x->tv_sec < y->tv_sec;
+}

src/devices/secplus_v1.c

@@ -18,7 +18,7 @@ Security+ 1.0  is described in [US patent application US6980655B2](https://paten
 */
 
 #include "decoder.h"
-#include <sys/time.h>
+#include "compat_time.h"
 
 /** @fn int _decode_v1_half(uint8_t *bits, uint8_t *result)
 
@@ -212,7 +212,7 @@ static int secplus_v1_callback(r_device *decoder, bitbuffer_t *bitbuffer)
         struct timeval cur_tv;
         struct timeval res_tv;
         gettimeofday(&cur_tv, NULL);
-        timersub(&cur_tv, &cached_tv, &res_tv);
+        timeval_subtract(&res_tv, &cur_tv, &cached_tv);
 
         if (decoder->verbose > 1)
             fprintf(stderr, "%s res    %12ld %8ld\n", __func__, res_tv.tv_sec, (long)res_tv.tv_usec);