From 801f1b160521079fae304c87a08be7f943bf1ebe Mon Sep 17 00:00:00 2001
From: wiire-a <wi7ire@gmail.com>
Date: Fri, 22 Dec 2017 12:04:11 +0100
Subject: [PATCH] Get elapsed time in a proper way

---
 src/pixiewps.c | 11 ++++++-----
 src/utils.h    | 25 ++++++++++++++++++++++---
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/src/pixiewps.c b/src/pixiewps.c
index 2015d58..206ca94 100644
--- a/src/pixiewps.c
+++ b/src/pixiewps.c
@@ -806,8 +806,9 @@ usage_err:
 			pfound = crack(wps, wps->pin);
 		}
 
+		struct timeval diff;
 		gettimeofday(&t_end, 0);
-		unsigned long ms_elapsed = get_elapsed_ms(&t_start, &t_end);
+		timeval_subtract(&diff, &t_end, &t_start);
 
 		printf("\n Pixiewps %s\n", SHORT_VERSION);
 		if (wps->verbosity > 1) {
@@ -859,8 +860,7 @@ usage_err:
 		else {
 			printf("\n [-] WPA-PSK not found!");
 		}
-
-		printf("\n\n [*] Time taken: %lu s %lu ms\n\n", ms_elapsed / 1000, ms_elapsed % 1000);
+		printf("\n\n [*] Time taken: %lu s %lu ms\n\n", diff.tv_sec, diff.tv_usec / 1000);
 
 		if (decrypted5) {
 			free(decrypted5);
@@ -1378,8 +1378,9 @@ usage_err:
 		k++;
 	}
 
+	struct timeval diff;
 	gettimeofday(&t_end, 0);
-	unsigned long ms_elapsed = get_elapsed_ms(&t_start, &t_end);
+	timeval_subtract(&diff, &t_end, &t_start);
 
 	k--;
 
@@ -1454,7 +1455,7 @@ usage_err:
 	else {
 		printf("\n [-] WPS pin not found!");
 	}
-	printf("\n\n [*] Time taken: %lu s %lu ms\n\n", ms_elapsed / 1000, ms_elapsed % 1000);
+	printf("\n\n [*] Time taken: %lu s %lu ms\n\n", diff.tv_sec, diff.tv_usec / 1000);
 
 	if (wps->warning) {
 		printf("%s", wps->warning);
diff --git a/src/utils.h b/src/utils.h
index 97f3388..7ac8303 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -230,10 +230,29 @@ unsigned int get_unix_datetime(char *s, time_t *datetime)
 	return 0;
 }
 
-/* Return the difference of time between the two in milliseconds */
-unsigned long get_elapsed_ms(struct timeval *start, struct timeval *end)
+/* Subtract the ‘struct timeval’ values X and Y
+   Return 1 if the difference is negative, otherwise 0
+   Reference: https://www.gnu.org/software/libc/manual/html_node/Elapsed-Time.html */
+int timeval_subtract(struct timeval *result, struct timeval *x, struct timeval *y)
 {
-	return (((end->tv_sec - start->tv_sec) * 1000000 + (end->tv_usec - start->tv_usec)) / 1000);
+	/* Perform the carry for the later subtraction by updating y */
+	if (x->tv_usec < y->tv_usec) {
+		const 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) {
+		const int nsec = (x->tv_usec - y->tv_usec) / 1000000;
+		y->tv_usec += 1000000 * nsec;
+		y->tv_sec -= nsec;
+	}
+
+	/* Compute the time remaining to wait, 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;
 }
 
 /* Convert an unsigned integer to a char array without termination */