hdparm: reduce possibility of numeric overflow in -T.

do_time                                              386     410     +24
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/0 up/down: 24/0)               Total: 24 bytes

diff --git a/miscutils/hdparm.c b/miscutils/hdparm.c
index 8a7204f29b39b015efbbce037762bb426e170432..1f85644d642af6eae2e1db90106f911c37a827c1 100644 (file)
--- a/miscutils/hdparm.c
+++ b/miscutils/hdparm.c
@@ -1375,10 +1375,13 @@ static void print_timing(unsigned long m, unsigned elapsed_us)
        printf("%5lu MB in %u.%02u seconds = %lu kB/s\n",
                m, sec, hs,
                /* Trying to not overflow 32-bit arith in m * CONST
-                * by keeping CONST not so big. + 1 prevents div-by-0. */
-               (m * (1024 * 1000000 / (64*1024))) / (elapsed_us / (64*1024) + 1)
-               // ~= (m * 1024 * 1000000) / elapsed_ms
-               // = (m * 1024) / (elapsed_ms / 1000000)
+                * by keeping CONST not so big. But elapsed_us / CONST2 
+                * also should not introduce big errors. Currently,
+                * 16000us is ~1.6% of 1 second.
+                * "+ 1" prevents div-by-0. */
+               (m * (1024 * 1000000 / (16*1024))) / (elapsed_us / (16*1024) + 1)
+               // ~= (m * 1024 * 1000000) / elapsed_us
+               // = (m * 1024) / (elapsed_us / 1000000)
                // = kb / elapsed_sec
        );
 }
@@ -1418,6 +1421,11 @@ static void do_time(int cache /*,int fd*/)
 
        /* Now do the timing */
        iterations = 0;
+       /* Max time to run (small for cache, avoids getting
+        * huge total_MB which can overlow on print_timing) */
+       elapsed2 = 510000; /* cache */
+       if (!cache)
+               elapsed2 = 3000000; /* not cache */
        start = monotonic_us();
        do {
                if (cache)
@@ -1425,11 +1433,11 @@ static void do_time(int cache /*,int fd*/)
                read_big_block(buf);
                elapsed = (unsigned)monotonic_us() - start;
                ++iterations;
-       } while (elapsed < 3000000 && iterations < max_iterations);
+       } while (elapsed < elapsed2 && iterations < max_iterations);
        total_MB = (unsigned long)iterations * TIMING_BUF_MB;
        //printf(" elapsed:%u iterations:%u ", elapsed, iterations);
        if (cache) {
-               /* Now remove the lseek() and monotonic_us() overheads
+               /* Cache: remove lseek() and monotonic_us() overheads
                 * from elapsed */
                start = monotonic_us();
                do {