Make "git clone" pack-fetching download statistics better

Average it out over a few events to make the numbers stable, and fix the
silly usec->binary-ms conversion.

Yeah, yeah, it's arguably eye-candy to keep the user calm, but let's do
that right.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

fetch-clone.c

@@ -130,12 +130,35 @@ int receive_unpack_pack(int fd[2], const char *me, int quiet)
 	die("git-unpack-objects died of unnatural causes %d", status);
 }
 
+/*
+ * We average out the download speed over this many "events", where
+ * an event is a minimum of about half a second. That way, we get
+ * a reasonably stable number.
+ */
+#define NR_AVERAGE (4)
+
+/*
+ * A "binary msec" is a power-of-two-msec, aka 1/1024th of a second.
+ * Keeing the time in that format means that "bytes / msecs" means
+ * is the same as kB/s (modulo rounding).
+ *
+ * 1000512 is a magic number (usecs in a second, rounded up by half
+ * of 1024, to make "rounding" come out right ;)
+ */
+#define usec_to_binarymsec(x) ((int)(x) / (1000512 >> 10))
+
 int receive_keep_pack(int fd[2], const char *me, int quiet)
 {
 	char tmpfile[PATH_MAX];
 	int ofd, ifd;
 	unsigned long total;
 	static struct timeval prev_tv;
+	struct average {
+		unsigned long bytes;
+		unsigned long time;
+	} download[NR_AVERAGE] = { {0, 0}, };
+	unsigned long avg_bytes, avg_time;
+	int idx = 0;
 
 	ifd = fd[0];
 	snprintf(tmpfile, sizeof(tmpfile),
@@ -146,6 +169,8 @@ int receive_keep_pack(int fd[2], const char *me, int quiet)
 
 	gettimeofday(&prev_tv, NULL);
 	total = 0;
+	avg_bytes = 0;
+	avg_time = 0;
 	while (1) {
 		char buf[8192];
 		ssize_t sz, wsz, pos;
@@ -181,14 +206,27 @@ int receive_keep_pack(int fd[2], const char *me, int quiet)
 			gettimeofday(&tv, NULL);
 			msecs = tv.tv_sec - prev_tv.tv_sec;
 			msecs <<= 10;
-			msecs += (int)(tv.tv_usec - prev_tv.tv_usec) >> 10;
+			msecs += usec_to_binarymsec(tv.tv_usec - prev_tv.tv_usec);
+
 			if (msecs > 500) {
 				prev_tv = tv;
 				last = total;
-				fprintf(stderr, "%4lu.%03luMB  (%lu kB/s)        \r",
+
+				/* Update averages ..*/
+				avg_bytes += diff;
+				avg_time += msecs;
+				avg_bytes -= download[idx].bytes;
+				avg_time -= download[idx].time;
+				download[idx].bytes = diff;
+				download[idx].time = msecs;
+				idx++;
+				if (idx >= NR_AVERAGE)
+					idx = 0;
+
+				fprintf(stderr, "%4lu.%03luMB  (%lu kB/s)      \r",
 					total >> 20,
 					1000*((total >> 10) & 1023)>>10,
-					diff / msecs );
+					avg_bytes / avg_time );
 			}
 		}
 	}