libsys: tsc_to_micros support for large TSC delta values

diff --git a/lib/libsys/tsc_util.c b/lib/libsys/tsc_util.c
index 815d8840f58265ed2217231e9cf34570db9fd8de..daa8a8c04116b6513a657a0546dbbace4070bc49 100644 (file)
--- a/lib/libsys/tsc_util.c
+++ b/lib/libsys/tsc_util.c
@@ -6,6 +6,7 @@
 #include <minix/u64.h>
 #include <minix/config.h>
 #include <minix/const.h>
+#include <minix/minlib.h>
 
 #include "sysutil.h"
 
@@ -93,22 +94,44 @@ micro_delay(u32_t micros)
 
 u32_t tsc_64_to_micros(u64_t tsc)
 {
-       return tsc_to_micros(ex64lo(tsc), ex64hi(tsc));
-}
+       u64_t tmp;
+       u32_t imv;
 
-u32_t tsc_to_micros(u32_t low, u32_t high)
-{
-       u32_t micros;
+       CALIBRATE;
 
-       if(high) {
-               return 0;
+       /* Various formulas provide various levels of accuracy depending on
+        * what still fits in a 64-bit number.
+        */
+       if (ex64hi(tsc) != 0) {
+               if (ex64hi(tsc) < ULONG_MAX) {
+                       tmp = mul64u(ex64hi(tsc) + 1, MICROHZ);
+
+                       if (ex64hi(tmp) == 0) {
+                               imv = div64u(mul64(tsc, cvu64(MICROHZ)),
+                                       calib_tsc);
+
+                               tmp = mul64u(imv, CALIBRATE_TICKS(Hz));
+
+                               if (ex64hi(tmp) == 0) {
+                                       /* Mid accuracy. */
+                                       return ex64lo(tmp) / Hz;
+                               }
+                       }
+               }
+
+               /* Low accuracy for large numbers. */
+               return div64u(mul64u(div64u(tsc, calib_tsc),
+                       MICROHZ * CALIBRATE_TICKS(Hz)), Hz);
        }
-       CALIBRATE;
 
-       micros = (div64u(mul64u(low, MICROHZ * CALIBRATE_TICKS(Hz)),
-               calib_tsc)/Hz);
+       /* High accuracy for small numbers (the common case). */
+       return div64u(mul64u(ex64lo(tsc), MICROHZ * CALIBRATE_TICKS(Hz)),
+               calib_tsc) / Hz;
+}
 
-       return micros;
+u32_t tsc_to_micros(u32_t low, u32_t high)
+{
+       return tsc_64_to_micros(make64(low, high));
 }
 
 u32_t tsc_get_khz(void)